Preventing Crystals in Grape Jelly, Jam, Syrup, and Juice

After you’ve gone to the trouble of foraging wild grapes or picking domestic grapes, juicing them, straining the juice, and making and processing juice, syrup, or jelly/jam, the last thing you want to find are crunchy bits in the jelly or syrup or a hard crystal formation at the bottom of a jar of juice. 

These crunch bits are crystals, usually of three types.
1) Tartrate Crystals – the naturally occurring components of grape juice
2) Sugar Crystals – improper cooking of the jelly or jam when the sugar is added.
3) Evaporation Crystals – loss of liquid

What are Tartrate Crystals?

Grape juice differs from many other fruit juices in that it contains naturally occurring amounts of both potassium and tartaric acid. At temperatures below 40F, these substances bind together to form crystals of potassium bitartrate better known as tartrate crystals. The crystals are benign or harmless so they pose no food safety risk but they are certainly unwanted encounters in juice, syrup or jellies.   Tartrate crystals can also form in grape jam.  In the wine industry, they are known as wine diamonds.

Preventing Tartrate Crystals

Regardless of the grape variety, color, or how the grapes were acquired, the problem is easy to solve with time and a fine strainer.

After juicing and straining the juice, allow the juice to sit undisturbed in covered containers for 24 – 48 hours in the refrigerator. My personal experience is that 48 hours is better than 24 hours if one has the time as crystals have continued to form in my juices after 24 hours. After the wait, slowly pour the juice through a jelly bag, cheesecloth, or very fine strainer into a clean container.  Be very careful as you reach the bottom as that is where you will find the tartrate crystals; they will appear as a rough, cracked substance on the bottom of the container.  Most of the crystals will be stuck to the container, but some may still be afloat.   

Once the tartrate crystals have been filtered out, the juice is ready to turn into jelly, syrup, or juice without the unwanted tartrate crystals. Recipes for jelly, jam, syrup, and juice can be found at the National Center for Home Food Preservation. The juice can also be frozen to be used later for making jelly.

What are Sugar Crystals?

Sugar is a crystal in its natural state and has an affinity to return to that form.  Even when dissolved in liquid as they are in jams and jellies, sugar molecules like to form into groups or crystals.  All they need is a party starter like an undissolved sugar crystal as a nucleus to draw other molecules of sugar towards it, re-forming crystals. Sugar crystals are not unique to grape sweet spreads. When making a sweet spread product or syrup regardless of fruit, it is important that the sugar is completely dissolved with no traces of crystals.

Preventing Sugar Crystals

Crystals throughout the jelly may be caused by too much sugar in the jelly mixture or cooking the mixture too little, too slowly, or too long. Learn how to prevent them from this Penn State Extension video.  Sweet spreads exhibiting sugar crystals are safe to eat.

Evaporation Crystals

Speckled crystals that form at the top of a sweet spread and scatter downward come when the product has been opened and allowed to stand; these crystals are caused by evaporation of liquid. This is more likely to happen with poorly capped, refrigerated jam or jelly.  White, fluffy mold on the surface of a jelly or jam is a sign of spoilage and should be discarded.

Crystallization due to evaporation can sometimes be reversed by gently reheating. Too much heat will cause the product to break down and not reset. The jar can be placed in hot water or carefully microwaving enough to melt the crystals. If melting is successful, a fresh or clean jar should be used.  Adding a small amount of lemon juice or corn syrup may also fix it.  In all cases, it is a temporary fix and the product usually goes back to crystallizing shortly.  A tight fitting lid is the best prevention. 

With just a little patience and careful preparation, crystals of all types can be prevented in grape products.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Recursos y Recetas para la Conservación Segura de Alimentos en Español

La conservación segura de alimentos comienza con recetas y recursos confiables y comprobados. El uso de prácticas y recetas de fuentes no comprobadas puede provocar enfermedades transmitidas por los alimentos. No se deben utilizar métodos de enlatado antiguos o recetas de familiares, amigos, vecinos o de sitios web de Internet que no hayan sido comprobados. Se pueden encontrar recetas seguras en el National Center for Home Food Preservation (NCHFP). K-State Research and Extension han traducido recetas del NCHFP al español. Siguiendo los enlaces que se proporcionan, se puede encontrar información confiable sobre enlatado y una amplia variedad de recetas para conservar los alimentos de manera segura utilizando las prácticas actuales de conservación de alimentos.

Kansas State University Publications in Spanish

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

September is National Sewing Month

September is National Sewing Month!  “Sew” it “seams” we should take time to honor the history of sewing and celebrate those who enjoy this art form or craft.  National Sewing Month was first celebrated in 1982 after President Ronald Reagan signed a proclamation “in recognition of the importance of home sewing to our Nation.” 

While sewing might imply the use of a sewing machine, it encompasses the many ways of stitching with thread and needle—garments, home décor, embroidery, needlepoint, cross-stitch, quilting, and all other forms of drawing a thread and needle through a medium. Sewing is a hobby enjoyed by millions of people from all walks of life throughout the world.

The art of sewing dates back to 25,000 B.C.E. when sewing was used to make clothing and shelter. Early materials consisted mostly of hides from animals and plant leaves. Thin strips of animal hide or long fibers drawn from plants made the first threads with bone and ivory being the first forms of needles.  Thomas Saint is credited with the invention of the sewing machine in 1750 followed by Isaac Singer’s prototype in 1851 that was to become the basis for the mechanization of sewing and the standard for the modern sewing machines we have today.  Prior to the 19th century, sewing was done by hand which allowed for perfecting skills as well as developing techniques for creative and decorative stitching.

Sewing has long been a favorite hobby of mine beginning with creations made with fabric scraps, thread, and needle for my dolls.  After my great-grandmother taught me to use her treadle machine, I turned out creations in mass.  As a 4-H member I enjoyed learning to use my mother’s electric machine and a pattern to fashion clothing for myself.  Each year was a new project with new skills.  That love of creating with fabric and a desire to understand fibers and fabrics led to my eventual college major.  While I never worked in the textile industry as I once envisioned, the skills and knowledge have given me a hobby and creative outlet that I still enjoy today.  And by joining with friends in guilds, I have learned and enjoyed many other forms of stitchery that have furthered by love of sewing. 

My deep love of thread and needle did not take root in my children; however, they were each fascinated enough to learn the skill of sewing with a machine to sufficiently take care of themselves.  Now I am sewing with my grandchildren who are intrigued with the creative process as they learn new skills.

While we may recognize the creative form of self-expression that sewing provides in the month of September, it is enjoyed all year.  During this month, there is a long list of retailers, bloggers, organizations, and others that promote “sewing” in an attempt to renew interest, share ideas, inspire, and teach.  If one was ever inclined to pick up thread and needle and try some form of sewing, the time to start is now. Creating quilts, clothing and other masterpieces not only develop new skills, but personal satisfaction, too. Sewing is a pleasurable activity to enjoy solo or with friends.  Happy sewing!

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Sweet Fruit Spreads – The Science of Successful Gelling

Sweet fruit spreads or jellied fruit products—jams, jellies, preserves, and marmalades—are usually cooked mixtures of fruit juice or fruit that form a thick, clear, slightly sticky substance known as a gel. When gelling works, the end result is a jelly characterized by a translucent color that quivers with a texture so tender that it may be cut easily with a spoon, and yet so firm that the angles produced by cutting retain their shape; OR a crushed fruit jam, preserve, or marmalade that is bright in color and spreads easily on breads or pastries.  And when it doesn’t work, the end result is usually a product that is runny like syrup or one that is tough and stiff. 

The key to creating a gel is a delicate chemistry or a balance of fruit, pectin, acid, and sugar along with the right temperature to get the product to set properly or arrive at a gelled state. When the “chemist in the kitchen” gets these factors correct, a hydrocolloid forms, or a web-like structure that holds the fruit and sugar in place evenly within the liquid. Here’s a look at the key elements of sweet spread chemistry.

Pectin, the thickener

After fruit, the most crucial ingredient in all sweet spreads is pectin.  Pectin is a naturally occurring soluble gelatinous polysaccharide that is present in ripe fruits.  Pectin is made up of large molecules that have a negative charge. The molecules have the potential to form a gel network when the molecules move together to trap and immobilize the sweetened fruit juice or fruit within it. Pectin is also water-loving, or hydrophilic, so it naturally wants to stick to water molecules.

Jams and jellies can be made using two methods: no added pectin and added pectin. Some fruit such as tart apples, blackberries, and cranberries are high-pectin fruits meaning they have sufficient pectin to gel on their own. Fruits like peaches and apricots, are low-pectin and don’t have enough pectin to gel on their own so need a supplement like a commercial pectin product.  There are also special pectin products for low-sugar and freezer sweet spreads.  Regardless of fruit, pectin levels are highest when the fruit is mature but still slightly under ripe. The National Center for Home Food Preservation has a list of pectin (and acid) content of fruits.

Commercial pectin is marketed in liquid and powder form. The two types cannot be interchanged so recipes must be prepared with the specified pectin product. Following the manufacturer’s instructions is imperative. Many people prefer to use commercial pectin because it can be used with any fruit, the cooking time is shorter and more standardized, and the yield is higher for a given amount of fruit. 

Acid, the neutralizer

Acid is the second essential component of any fruit preserve. Without acidity, pectin molecules repel one another just like the same ends of magnets. The positive ions on the acid molecules neutralize the charge allowing the pectin molecules to move together forming a gel network.

Fruits that are high in both pectin and acid will gel on their own, while those with lower acid levels will not. To compensate for low-acid fruits, lemon juice is added with bottle lemon juice being the best source due to a consistent pH level.  Commercial pectin products contain acids that help ensure gelling.

Sugar, the water grabber

The third essential component is sugar.  Without sugar, pectin molecules prefer to bind with water molecules rather than with one another.  Because sugar is hygroscopic (readily attracts water), it ties up the water forcing the pectin molecules to connect with one another to form the gel network. Cane or beet sugars are best for jams and jellies. Light corn syrup or light, mild honey can be used to replace part, but not all, of the sugar. or best results, use tested recipes that specify honey or syrup. Artificial sweeteners cannot be substituted for sugar in regular recipes because the sugar is needed for gel formation. Sugar also acts as a preservative.

Temperature, the evaporator

Temperature plays a big part in getting the three essential components to work together to create a gel.  When using a commercial pectin product, following the directions carefully will insure that the proper temperature has been reached to create a gel. 

When a spread is prepared with no added pectin, temperature is critical.  The pectin in fruit becomes water soluble when it is heated.  Heating fruit juice or fruit with sugar to a rolling boil causes water to evaporate and the sugar to reach an appropriate concentration. The ratio of sugar to water is measured through temperature and is known as the gelling point. At the gelling point, enough water has evaporated to strengthen the pectin network enough to slow the movement of water to form a spreadable gel. Arriving at the gelling point quickly is best to retain the fruit’s best flavor, color, and the pectin’s thickening power.  Pectin will begin to break down and lose its ability to gel if cooked beyond the gelling point.  Evaporation can be sped up by using a wide pan to expose more surface of the product.

There are three methods of testing for the gelling point in sweet spreads made without added pectin—temperature test, spoon or sheet test, and freezer test.[1]  Of these, the temperature test is the most dependable but altitude must be considered.  The gelling point is 220°F or 8°F above the boiling point of water at sea level. For each 1000 feet of altitude above sea level, subtract 2 degrees F. For instance, at 1,000 feet of altitude, the jelly is done at 218°F; at 2,000 feet, 216°F, etc. 

Chemical Equation, the directions

When making sweet spreads every ingredient and processing step is critical. Following tested recipes, using fruit at the right maturity level, and getting the balance of pectin, acid, and sugar correct can affect the quality and safety of the spread. Making double batches or reducing the amount of sugar in the recipe may interfere with gel formation. Regardless of whether a recipe is made with added pectin or no added pectin, all cooked spreads must be processed in a water bath canner with the processing time adjusted for altitude.   

Despite best efforts to do everything right, sometimes problems do occur.  When things go awry, consider the problem and troubleshoot using one of these resources:
Troubleshooting Jelly and Jam Problems,
Causes and Possible Solutions for Problems with Jellied Fruit Products, 
or watch the 
Troubleshooting Jams & Jellies video.
However, before doing anything, let the product sit for at least 12 hours after processing to allow time to set up. Some sweet spreads can take up to two weeks to completely set so if used soon after making, it may be softer than it will be later.

Should there be need to remake a sweet spread due to a soft gel, carefully read and follow directions in Remaking Soft Jams and Jellies by Washington State University Extension.  Should the product be too stiff, the National Center for Home Food Preservation offers suggestions on how to remedy the product sufficiently to provide a mixture that may spread more easily.

Regardless of whether the product turns out perfectly or otherwise, a sweet spread that has been processed as recommended in a boiling water canner and has a solidly sealed vacuum lid, is safe to eat and can be stored at room temperature like other sweet spreads with good quality expected for a year.[2] (The quality loss may be quicker in light-colored and/or reduced-sugar products and it may be desirable to use these within 6-8 months.)

Understanding the functions of the ingredients and the science of gelling can truly help the “kitchen chemist” successfully make sweet spreads.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Potentially Deadly Canning Mistakes

Home canning is an excellent way to preserve garden produce and share it with family and friends, but it can be risky—or even deadly—if not done correctly and safely.  The potential culprit is botulism. 

Although it’s a rare occurrence, botulism is a serious illness caused by a bacterium toxin, Clostridium botulinum, that attacks the body’s nerves. It can cause difficulty breathing, muscle paralysis, and even death.  Clostridium botulinum is commonly found in soil, on raw fruits and vegetables, on meat and fish, and many other foods and surfaces. Improperly home-canned, preserved, or fermented foods can provide the right conditions for the bacteria to make the toxin.  One cannot see, smell or taste the toxin, yet if ingested, even a small amount can be deadly. 

To avoid concerns about botulism, steer clear of these canning mistakes [1].

Making Up Your Own Recipe
Use only up-to-date, scientifically tested recipes approved by the USDA and follow directions exactly.  Good sources are The Complete Canning Guide, the National Center for Home Food Preservation, So Easy to Preserve, and land-grant university publications.    Without scientific testing, there is no way to know how long the product needs to be processed to be safe.

Adding Extra Starch, Flour or Other Thickeners
Starches slow the rate of heat penetration into the product and can result in under processing.  Clear Jel® is recommended as a thickener for canned pie fillings. If a product is not as thick as desired going into the jar, it can be thickened at the time of use.

Adding Extra Onions, Chilies, Peppers, or Other Vegetables to Salsas or Sauces
Tested recipes specify the quantity of vegetables allowed to keep the salsa or sauce within the safe pH range.  Most vegetables are low-acid and adding extra vegetables will dilute the acidity and result in an unsafe product.  While it is dangerous to add more vegetables to salsa and sauce recipes, fewer may be used for a milder flavor.  Extra ingredients can be added at the time of use.

Canning by Electric Pressure Cooker, Oven, Open Kettle, Microwave, or Dishwasher
Boiling water bath or pressure are the only approved canning methods. Any other method should be avoided as foods will be under processed and unsafe. Heat is conducted by air in an oven which is less efficient than water or steam. As a result product temperature never exceeds the boiling point; jar breakage is also a possibility. Open-kettle canning, placing hot food in jars and sealing with no further heat treatment, has been considered an unsafe home canning practice since the 1980’s due to insufficient heat to destroy bacteria [2]. Microwaved food reaches 212°F but heating is not uniform; in additon, there is a danger of jar explosion within the microwave oven or as food is being removed [2]. The water temperature of the dishwasher’s cleaning and rinsing cyles is far below that required to kill harmful microorganisms. While electric pressure cookers use pressure for cooking, they do not meet the appliance standards for home pressure canning, even if marketed as safe for pressure canning. Washington State Extension explains all the reasons why electric pressure cookers should not be used for home canning in Canning in Electric Pressure Cookers.

Not Making Altitude Adjustments
The temperature at which water boils is affected by barometric pressure which is reduced with elevation or altitude. When water doesn’t reach the normal boiling temperature, undesired pathogens may survive the canning process. These pathogens could multiply in the canned food and cause sickness.  Processing times and temperatures for recipes in most canning resources are based on canning at an elevation of 1,000 feet above sea level or lower.  When canning at a higher elevation, one must add more pounds of pressure for pressure canning and more processing time for water bath canning.  See charts prepared by South Dakota State University Extension for altitude adjustments.

Not Venting the Pressure Canner
Trapped air inside a pressure canner lowers the temperature obtained for a given pressure and results in under processing.  To be safe, the USDA recommends that all pressure canners be vented 10 minutes before they are pressurized.

To vent a canner, leave the vent pipe (steam vent) uncovered (or manually open the petcock on some older models) after you fill the canner and lock the canner lid in place. Heat the canner on high until the water boils and generates steam that can be seen escaping through the open vent pipe or petcock. When a visible funnel-shape of steam is continuously escaping the canner, set a timer for 10 minutes. After 10 minutes of continuous steam, you can close the petcock or place the counterweight or weighted gauge over the vent pipe to begin pressurizing the canner. [3]

Failure to Acidify Canned Tomatoes
Because the pH of tomatoes is an unknown, the USDA recommends that bottled lemon juice be used to lower the pH of the product to be unquestionably safe.

Rushing the Pressure Canner Cool-Down Time
The natural cool-down of the canner is part of the tested processing time.  Hurrying this process will result in under-processed food and siphoning of liquid from the jars.  It may also cause jar breakage.

Allowing “Hot Pack” Foods to Cool in Jars before Processing
Processing times are based on the food being hot at the beginning of the processing.  Foods not starting hot could be under processed. Further, the rule, “hot foods hot and cold foods cold” applies; when foods are held between 40 and 140°F, bacteria can grow rapidly.

Processing Low-Acid Foods in a Water Bath
Canning low-acid foods requires special care. This includes red meats, fish, poultry and all vegetables (except for acidified tomatoes). Low-acid foods can support the production of the deadly botulism toxin if these foods are not processed properly in a pressure canner. A pressure canner heats food to high temperatures (240-250 degrees F or higher) and destroys the spores that produce the botulism toxin. A boiling water bath canner, which can be used for canning pickles or fruit, heats food to boiling temperature (212 F), which is not high enough to ensure safety for canning vegetables and other low-acid foods.[4]

Home canning is perfectly safe but needs to be done correctly.  If you are new to canning (or need a refresher), check out Safe Home Canning Basics, by Minnesota University Extension to learn about preventing botulism and other key issues to be aware of when preserving food by home canning.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Canned Tomatoes – Answers to Frequently Asked Questions

Tomatoes are the most popular food for canning at home.  They are versatile, abundant, and easy to can. There is no doubt that tomato canning season is here as the number of “tomato canning” questions rise—floating, separation, loss of liquid, air bubbles.  Do any of these problems affect the safety?   AnswerLine is here to answer these questions.  

Float

Floating tomatoes (tomatoes or tomato pieces at the top of the jar, liquid at the bottom) may be a visual disappointment but does not affect the safety of the product. Floating is more likely to happen with whole or quartered tomatoes and with a raw pack.  The floating is caused by the natural air and water in the tomatoes which releases during processing. Raw food has a lot of air in it. The volume of food put in a jar before processing might actually only be ¾ food and ¼ air trapped inside the food. During processing, this air will escape from the food and rise to the top of the jar. Float can be minimized by choosing fresh, firm tomatoes, reducing the amount of liquid in the jar (replacing with product), packing the jar as firmly as possible without crushing the tomatoes, removing air bubbles, and using a regular mouth jar. Sometimes turning the jars upside down after they have cooled for 24 hours and letting them rest for a period of time will bring the liquid and solids back together.  Canning crushed tomatoes and/or using a hot pack often eliminates the problem. 

Separation

Sometimes crushed or puréed (juice) tomatoes will separate in the jar into tomato solids and liquid. Separation is another visually disappointing issue that does not affect safety. When tomatoes are cut or crushed before heating, exposure to the air activates a natural enzyme, Pectose (Pectinesterarse), found in high concentrations in tomatoes. The enzyme is activated when tomatoes are cut. This enzyme breaks down pectin which causes the liquids and solids to separate.  Heating tomatoes immediately after they are cut or crushed to 180F (82C) inactivates this enzyme.  This is the reason that many tested recipes direct one to cut small quantities of tomatoes and heat them in batches.  Gently shaking the jars after the product has cooled for 24 hrs may bring the solids and liquid back together.

Loss of Liquid

Loss of liquid does not cause food to spoil, though the food above the liquid may darken. If, however, the loss is excessive (for example, if at least half of the liquid is lost), refrigerate the jar(s) and use within 2 to 3 days.[1]  And jars with milder liquid loss should be used sooner rather than later so place them at the front of the shelf so they get used first.  Penn State Extension advises on the three likely causes of liquid loss or siphoning from the jar during processing of tomatoes or other fruits and vegetables—raw pack, rapid fluctuation of temperature in the canner, and removing the jars too quickly after processing. In addition to the causes noted, improper headspace and loose bands are other sources of liquid loss.  Food expands during processing and if a jar is overfilled there is insufficient room for the expansion.  When this happens, water will push out to make room for expansion. If canning ring bands are too loose, liquid will escape and may also cause seal failure. And like floating and separation, removing air bubbles from the jar prior to lidding helps to lessen liquid loss.

Air Bubbles

Removing of air also known as de-bubbling prior to processing is an important step in canning. Air trapped in jars can interfere with the jar’s ability to drive out the extra air in the top causing too much headspace, floating, loss of liquid, and a poor or no seal. Additionally, too much air space results in canned product above the canning liquid which can lead to discoloration and the development of off-flavors. Ball and Norpro make a bubble remover and headspace tool designed for air removal but a plastic or silicone knife or spatula handle will do the same; any tool used should be heat resistant to handle the heat of a hot pack.  Do not use anything metal to remove air as it may cause hairline cracks in the jar.  Simply run a bubble popper around the edges of the jar, gently shifting the food, so that trapped air is released as much as possible. After the air bubbles have been removed, more liquid may need to be added to the jar to ensure proper head space.

After processing, tiny air bubbles may be noticed in the product.  If these bubbles are inactive, they are benign or harmless.  If the bubbles are actively moving or fizzing up to the top of the jar when opened, the product may be fermenting or contaminated. Products with active air bubbles should not be used and properly discarded.

Despite one’s very best efforts to diminish floating, separation, loss of liquid, or air bubbles, it seems that there is one more non-scientific reason—the phase of the moon! Or that it just happens!  As long as the jar seals and there is at least half of the liquid in the jar, the tomatoes are safe inside the jar.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

The Case for Bottled Lemon Juice in Canning

Many home preservers often wonder why tested and USDA approved canning recipes call for bottled lemon juice. This is especially true when it involves tomatoes and making jams.  Why not fresh squeezed lemon juice?

A USDA RECOMMENDATION

It is a USDA recommendation that bottled lemon juice be used.  And consistent with the recommendation,  reputable canning sources will agree that the best source of lemon juice for canning is commercially bottled lemon juice, as opposed to the juice of a fresh lemon.  The reason for the recommendation is that bottled lemon juice has been uniformly acidified or standardized per FDA regulations: “lemon juice prepared from concentrate must have a titratable acidity content of not less than 4.5 percent, by weight, calculated as anhydrous citrus acid.”  With a guaranteed pH (5 percent2), there is a consistent and known acid level which is essential for the critical safety margin in canning low-acid foods and for making jams gel properly.  

Acid strength is measured on the pH scale. The scale starts with strongest acid at 1 and declines in strength as the number increases to 14, the strongest alkali. The lower its value, the more acid in the food. The neutral point is 7, neither acid nor alkaline.  The amount of acid in canned food is critical to deter the growth of micro-organisms and insure that the food is safe. Foods with a pH less than or equal to 4.6 are labeled “high-acid” foods. Those with a pH greater than 4.6 are “low- acid.” This distinction is very important because only high-acid foods can be processed safely in a boiling water bath. Low-acid foods must always be processed in a pressure canner; if not, they can support the growth of the potentially harmful bacterium, Clostridium botulinum.

The pH of fresh lemon juice is inconsistent due to variety, maturity, weather conditions during growth, soil, fertilizer, rootstock, and storage conditions. There are even variations in acidity within a single variety. Lemons grown in hot climates tend to be less acidic than those grown in cooler climates.  Lemon juice contains both ascorbic and citric acid; since ascorbic acid is destroyed by heat, only citric acid is measured.  The average acid level of fresh lemon juice is about 5 percent, thus the “natural strength” labeling on the lemon juice bottle. 

While acid consistency is the reason for using bottle lemon juice, bottled lemon juice is made from concentrate and preserved with sulfites. For people allergic to sulfites, bottle lemon juice may be a health hazard.  If you or family members have a sulfite sensitivity or allergy, substitutes for bottled lemon juice include bottled lime juice (not Meyer or key lime) or frozen lemon juice (not lemonade) in equal amounts as bottled lemon juice or citric acid in appropriate ratios. Citric acid, sold as a white crystalline powder and not the same as ascorbic acid, is available where canning supplies are sold. It can safely be used to acidify foods if used correctly. Vinegar should not be used to replace bottled lemon juice unless a tested recipe allows it because white vinegar is weaker in acid strength. Equal amounts of bottled lemon juice can be used to replace white vinegar in recipes calling for vinegar, but not the reverse. When vinegar is an acceptable substitute, it will affect the flavor of the food.  Never change the amount of acid, dilute with water, or substitute acid sources unless the recipe specifically allows you to do so.  Aspirin should not be used as a substitute in canning. It cannot be relied on to lower pH or prevent spoilage [3].

ACIDIFYING TOMATOES FOR SAFE CANNING

When canning products with an unknown pH as acid foods, they must be acidified to a pH of below 4.6 with lemon juice or citric acid. Tomatoes, usually considered an acid food, and figs are two examples where the pH values hover near or above 4.6. When acidified with lemon juice or citric acid, they may be processed as acid foods [1][2] making them safe for boiling water bath or atmospheric steam processing. Directions from the National Center for Home Food Preservation [3] for acidification of tomato products to insure safe acidity in whole, crushed, or juiced tomatoes state:  Use 2 tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, use 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid. Acid can be added directly to the jars before filling with product. Sugar may be used to offset the acid taste, if desired. 4 tablespoons of a 5 percent acidity vinegar per quart may be used instead of lemon juice or citric acid. However, vinegar will likely cause undesirable flavor changes. Tomato salsas must also be acidified.[4] To get an idea of how much difference bottle lemon juice makes, see Table 1 in the publication Why Add Lemon Juice to Tomatoes and Salsas Before Canning? by North Dakota State University.

pH MATTERS WITH JAMS

While many factors are involved in getting jams to “set” or gelatinize, pH plays a key role. When fruit is cut and heated with sugar, pectin strands are released from the fruit cells.  The freed pectin strands repel each other because they carry a negative electric charge.  Lemon juice lowers the pH of the jam mixture and neutralizes the negative charges on the strands of pectin allowing them to move together into a network to “set” the jam.  The optimal pH for gelatinization is between 2.8 and 3.5. The best way to achieve this level of acidity is to use commercially bottled lemon juice.  A second reason for using bottled lemon juice in jam recipes is to prevent the growth of bacteria and insure safe canning. With a lower pH, jams can be processed in a boiling water bath for a small amount of time dependent on altitude. 

Whether using bottle lemon juice to acidify tomatoes or getting jam to “set,” bottled lemon juice has a ‘best used by’ date. Keeping the product in the fridge may extend its date but it is best to use a fresh bottle when canning or making jam to insure that the juice is at its best.

The verdict is in.  The best way to insure a safe or desired pH for canning low-acid foods or jam gelatinization is to go with a commercially bottled lemon juice. Bottled juice is controlled and standardized with the acid content assured and more reliable than fresh lemons.  Fresh lemons, however, make excellent lemonade!

_____________________________

1 Code of Federal Regulations (Title 21, volume 2, revised April 1, 2010)

2 Green, Janet; Hertzberg, Ruth; Vaughan, Beatrice (June 2010). Putting Food By, Fifth Edition (p. 119). Penguin Books Ltd. 

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Freeze Drying – A New Option for Home Food Preservation

Canning, pickling, freezing, drying, and fermenting are well-known methods of preserving fruits and vegetables for future use.  These processes have been used for generations and made simpler and safer over time with the help of science and innovation.  Freeze drying (lyophilization) is now an option for home food preservation.  HarvestRight, a company in Salt Lake City, Utah, introduced a freeze drying unit for home use in 2018 that has excited the curious of food preservers.  While still an uncommon home appliance, freeze drying is becoming a sought-after means for preserving food at home and the units are showing up at some retailers [1].

Freeze-dried vegetables for soups made from carrots, leek, celeriac, lovage, parsnips and parsley

Freeze drying is not a new process.  The process may date back to the 13th century with the Incas using a simple process to preserve potatoes in the Andes.  The first patent was issued in 1934.  During World War II it was used to safely transport blood serum and penicillin to the battle field.   In the 1950s–1960s, freeze drying began to be viewed as a multi-purpose tool for both pharmaceuticals and food processing and became a major component of space and military rations. Freeze drying has been widely used in the food industry to extend the shelf-life of food while maintain quality. Freeze-dried foods have been available commercially for some time and offer consumers fast meal prep, emergency prepardeness, and portable food. Freeze-dried foods also offer convenience as they can be eaten “as is” (except for raw meat, poultry, seafood, and eggs), added directly to recipes, or rehydrated and used the same as fresh food.

In a nutshell, freeze drying works by freezing the material, then reducing the pressure and adding heat to allow the frozen water in the material to change directly to a vapor (sublimate).  The process removes 98-99 percent of the moisture in food making it a superior method for preserving food. (An example of a freeze dried food are the berries in commercial cereals that feature real berries.) Freeze dried foods retain 97 percent of their nutrients and natural enzymes and original flavor and color [2] .  Additionally, freeze-dried food is really easy to use; food comes back to its original pre-freeze dried state by just adding water.  Since nearly all water has been removed, freeze-dried food is light making it a favorite for camping and backpacking.  A bag of apples that weighed 10 pounds when fresh, weighs about one pound after being freeze dried [3].

Freeze drying produces high quality foods that are safe as long as they were handled properly prior to freeze drying and once the packaging is opened.  It is important to note that freeze drying does not kill bacteria or other microorganisms; they remain viable, but dormant, despite the extreme conditions of freeze drying.  Any bacteria or microorganism on raw foods prior to freeze drying will reactivate upon rehydration. Therefore, food items that are traditionally cooked before eating must also be cooked before eating as a freeze-dried food.

A freeze dryer is not a fancy food dehydrator. While a freeze drying unit and a dehydrator both remove moisture from food so that microorganisms cannot grow and enzyme action is slowed down, a dehydrator uses low heat and a fan to remove 80-90 percent of the moisture content from food1.   As food is dehydrated, it typically shrinks up and develops a leathery feel and appearance; rehydration is slow and foods do not return to their natural state. Dehydration doesn’t change the fiber or iron content of food. However, dehydration can break down vitamins and minerals during the preservation process and retain less of their nutritional value when compared to freeze-dried food. Dehydration tends to result in the loss of Vitamins A and C, thiamine, riboflavin and niacin. [4]. With a lower moisture content, freeze-dried foods offer a shelf life of 25 years [2] compared to 4 months to 1 year for dehydrated foods [5]. Freeze-dried foods rehydrate faster and also retain their original shape, texture, and color. A far greater variety of foods can be freeze dried than can be dehydrated [6].  Both dehydrated and freeze-dried foods store best in airtight containers with an oxygen absorber for long term storage.  Because dehydrated foods rehydrate slowly, they do not readily absorb moisture if exposed to less than optimal conditions; freeze-dried foods, on the other hand, are like a sponge and can go quickly from crisp to soggy when exposed to moisture.

A home freeze drier puts you in control.  Commercially prepared freeze-dried foods are pricey and often have added ingredients.  HarvestRight suggests that home freeze-dried food is one-third the cost of store bought. Freeze drying versatility also allows for the preservation of dairy, meat, produce, and complete meals. 

Display at a local store featuring the medium-sized unit.

Investment in freeze drying equipment is an important consideration, too.  Be prepared for ‘sticker shock’ as the units are expensive and require considerable space in the home.  Equipment cost ranges from four to eight times more than conventional drying equipment and the energy required is almost double that of conventional drying.  Buying a Home Freeze-Dryer: What to Know Before You Go by Utah State University Extension and Let’s Preserve:  Freeze Drying by Penn State Extension explain this in more detail. Besides the initial investment in a freeze drying unit, packaging after drying is another consideration.  When correctly packaged, freeze-dried items can be stored safely for many years.   To increase shelf life, properly sized single-use food grade oxygen absorbers—small packets that attract and retain the oxygen in a package—must be included in whatever type of packaging is chosen.  While glass jars, cans, zip bags, and vacuum sealed bags can be used, opaque Mylar® bags are preferred; they block out air and light during storage, can be resealed once opened and take up less space than glass jars or cans. Mylar® must be used with an oxygen absorber and heat-sealed with an impulse (heat) sealer.

The options for food preservation are many.  Each method brings something different to the table. The flavors and textures are different and how we use the food preserved is different. If long term food storage or portable food storage is the goal, freeze drying is an option to consider.  Imagine rehydrating lasagna on a camping trip!

________________________________________

1Andress and Harrison. 2014. “So Easy to Preserve” 6th ed. Bulletin 989, Cooperative Extension Service. The University of Georgia, Athens.

Guide to Freeze Drying – The Miracle of Food Preservation, HarvestRight.

Reference to any commercial product, process, or service, or the use of any trade, firm, or corporate name is for general informational purposes only and does not constitute an endorsement, recommendation, or certification of any kind. Persons using such products assume responsibility for their use and should make their own assessment of the information and whether it is suitable for their intended use in accordance with current directions of the manufacturer.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Get Fired UP! Tips for Baking on the Grill

Nothing says summer quite like the smell and sound of food sizzling on the grill.  In previous blogs, tips for grilling meat and sides—fruits and vegetables—were shared.  Did you know that you can use your grill as an oven for baking, too? 

Anything you can bake in a kitchen oven – casseroles, pies, cookies, brownies, pizza, coffee cake, bread – can be baked on a gas or charcoal grill all summer long without heating up the kitchen.  While you don’t need to adjust the recipes, you do need to figure out how to turn direct heat into indirect heat. Every grill is different, so you’ll need to figure out what will work best with what you’ve got. It’s also a good idea to start with something simple (I started with brownies and pizza) and work up to more complicated baked goods. It may take some time to get it just right, so be patient and write down what you learn along the way. Here are some tips to get you started.

Start with a clean grill.  You don’t want your baked goods to taste like last night’s onions or brats or whatever was grilled last.

Preheat the grill.  Weber [1] has some great tips for preheating and baking with both gas and charcoal grills.  I have a gas grill and have found that preheating to 25⁰ F higher than the desired temperature is helpful.  Heat is lost when placing the unbaked items inside and is not regained as quickly as in an oven.  Every grill is different, so getting the temperature right may take some experimenting. If your grill doesn’t have a built-in thermometer as mine does, invest in one as knowing the temperature inside the grill is important.

Use indirect heat.  To create indirect heat, turning off some burners on a gas grill will be necessary to create indirect heat.  My grill has three burners so I turn 1 and 3 to medium and turn off 2 allowing me to bake in the middle of the grill.   Sometimes, I find the need to turn off both 1 and 2 and use only 3 for heat giving me more space on the grill for baking.  For charcoal grills, move the charcoal to one side of the grill and bake on the side away from the heat.

Choose baking dishes that withstand intense heat.  A pizza stone or a cast iron skillet are perfect options. I bake cookies, pizza, and bread on my pizza stone and casseroles, cakes, brownies, cobblers, and crisps in my cast iron skillet!  Avoid using glassware even if it is Pyrex® as it is prone to breaking despite using indirect grill heat. Grill mats are another options for some baked goods.

Choose recipes that are forgiving.  Since grill baking is less precise than oven baking, choose recipes that will withstand the fluctuating temperatures on a grill.  Cakes are the most finicky. I’ve had the best luck with pizza, brownies, fruit crisps, and casserole dishes.  Flatter, artesian-type breads usually do well for me, too.

Keep an eye on the temperature while baking.  Grill temperature fluctuates more than the oven so sometimes adjustment of temperature is necessary.  I’ve found this to be particularly true when there is wind. Check the temperature frequently while baking and adjust as necessary.

Avoid the temptation to lift the lid.  Lifting the lids releases a lot of heat.  Use your nose as much as possible and if you must lift the lid, make it quick.  It takes a little practice to know that distinct perfect—DONE—smell.  (We all know the one of food baked too long.) 

Grill baking time may be different than oven baking time.  I find that baking goes faster in the grill than in my oven and that the same recipe can vary in time depending upon grill conditions.  While the traditional toothpick inserted into the middle technique works well to determine doneness, it is helpful to insert a temperature probe into the center of the unbaked product to determine when some baked items are done.  For example, cake is done when the probe reaches 210⁰ F.

Baking in a grill takes experimentation and patience.  Grilled baked goods may not turn out the same as baked in an oven.  There may be signs of hot spots or browned more than usual on the bottom.  As long as they are not over-baked (burned), they will still be tasty.  By using your grill, you’ve kept the kitchen cool.  And as a bonus, in the event of a power outage, you will have learned a means of baking without an oven.  Check out Get Fired UP!  Tips for Grilling Meat and Sides—Fruits and Vegetables for additional grilling tips and get into summer grilling in a big way!

This blog was reviewed by Anirudh Naig, Associate Professor in Hospitality Management & State Extension Specialist for Retail Food Safety at Iowa State University.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

Get Fired Up! Tips for Grilling Sides – Fruits and Vegetables

Nothing says summer quite like the smell and sound of food sizzling on the grill.  In a previous blog, tips for grilling meat were shared.  While the king of the grill might be meat, the produce aisle is full of goodies that take on amazing flavors when grilled.  Grilling brings out the sweet, toasty, and caramelized flavors that other cooking techniques do not. Besides shining with flavor, there’s very little prep involved.

Here are a few pointers to perfect your vegetable and fruit grilling technique:

  • Wash, trim, and peel as necessary.
  • Make sure to clean the grill grates with a wet cloth or paper towel. If using a metal brush, besure that there are no bristles left behind. Bristles can attach to food and if consumed can cause choking or affect the digestive tract.
  • Prepare pieces that are consistent in size to ensure even cooking.
  • To prevent sticking and add flavor, brush or toss with 1-2 tablespoons oil per pound. Excessive oil will cause flare-ups.  Add any seasonings desired with the oil.
  • Use a perforated grilling basket or grilling mats to prevent items from falling through the grates.  I prefer the grilling mats, copper or non-stick PTEE (PFOA free).  Mats make grilling so easy and still allow foods to take on the grill flavors and coveted grill marks. They are easy to clean and keep the grill grates clean, too. 
  • Stainless steel kabob skewers are best for grilling because they don’t roll and they are easy to flip. Wood or bamboo skewers should be soaked in water for 30 minutes before using to keep them from burning.
  • When grilling a variety of vegetables, be sure to start with the ones that take the longest to cook and add the others incrementally, saving the quickest-cooking ones for last. Produce should be removed before it is soft as it will continue cooking once removed from grill.  On a medium hot grill it typically takes 10 minutes or less for most vegetables to cook.
  • Apply barbecue or other sweet sauce or coatings toward the end of cooking so it has time to glaze but not burn.

Guidelines for Grilling Individual Vegetables

Here are some great tips for grilling individual vegetables from Alexandra Grenci with Rutgers Cooperative Extension [1].

  • Asparagus: The ends of asparagus spears can be tough, so trim them off, then toss the spears in olive oil and salt/pepper and grill for 4-5 minutes over a medium-high grill, then turn and grill another 4-5 minutes.
  • Bell peppers: Remove the core and seeds, then slice each pepper into about four separate sections. Toss with olive oil and salt/pepper and grill over a medium-high heat for 4-5 minutes. Then turn and grill 4-5 minutes longer.
  • Cabbage: Cut the cabbage in half and then slice each half into thick 1-inch slices. Toss with olive oil and your favorite seasonings. You can skewer each big slice to keep it from falling apart. Grill over a medium-high grill for about 10 minutes, then turn and grill for another ten minutes.
  • Cauliflower: Cut the cauliflower into big florets, toss in olive oil and your favorite seasonings and then skewer. Grill over medium-high heat, turning often, for about 10 minutes or until the cauliflower is tender and lightly charred.
  • Corn: Some people like to grill corn with the husks still on, but that’s just steaming the corn, really. By removing the husks and the silk and cooking the corn directly on the grill, the kernels get lightly blackened and caramelized, bringing out tons of sweet corn flavor. You should grill corn over a medium grill for 4-5 minutes, turning frequently.
  • Eggplant: Cut the eggplant into ½-inch slices. Brush them with oil or a simple balsamic vinaigrette, toss with your favorite spices. Grill over a medium-high grill for about 5 minutes, then flip and grill for 5 minutes longer.
  • Mushrooms: Toss white or brown button mushrooms with olive oil and Kosher salt. Then skewer and cook over a medium-high grill for 7-8 minutes, turning frequently. You can also grill a whole Portobello mushroom cap directly on the grill. Grill them smooth-side-down for 8-9 minutes.
  • Onions: Large, sweet onions like Vidalias are great for grilling, as are red onions. Just peel them, cut them into ½-inch slices, toss them in olive oil and your favorite seasonings and cook over a medium-high grill for 2-3 minutes, then turn and grill 2-3 minutes longer. A skewer can be handy to hold the onions together on the grill.
  • Tomatoes: Cherry tomatoes can be skewered and grilled whole, for 3-4 minutes over a medium-high grill. Be sure to turn them frequently so that they cook evenly. You can also grill plum tomatoes. Cut them in half the long way, remove the seeds and grill for four minutes, then turn and grill for four minutes longer.
  • Zucchini and yellow squash: Cut into ½-inch pieces lengthwise, toss in olive oil and salt /pepper and cook over medium-high grill for 4-5 minutes. Then turn and grill another 4-5 minutes longer.

Guidelines for Grilling Fruit

  • Just about any fruit can go on the grill as long as it is fairly firm and not overripe. Peaches, melons, pineapple, pears, tomatoes, bananas, and figs are just some of the fresh fruits that will hold their shape over the coals.
  • Most fruit is fairly fragile, so cut fruit into large chunks, slices, and wheels to help it maintain its structure as it heats up and breaks down. Smaller fruits like grapes and blueberries can be prepared on a skewers.
  • Grilled fruit kabobs are a win at any picnic or barbecue.  Any combination of fruits can be used and they make a perfect appetizer or dessert.
  • In addition to a small amount of oil (neutral) or butter, fruits are best mixed or brushed with a bit of citrus juice (lemon juice prevents browning), maple syrup, or honey prior to grilling.  For additional flavor, try adding cinnamon, chili powder, smoked paprika or a curry blend.
  • Grill fruit over high heat for three minutes without moving or turning it to get the perfect sear (and coveted grill marks). Flip and cook for one to three minutes more.
  • Grill fruit flesh-side down.  If you place it skin side down, you’ll miss the caramelized texture and the heat won’t get through the rest of the fruit evenly.
  • Fruits contain a lot of water, which makes them very hot once they are cooked. Be sure to allow time for grilled fruits to cool down a little before serving.
  • Even though grilled fruit makes a great dessert, it is not just for dessert.  Grilled fruit can be used as a side dish, in fresh salsas, and as part of delicious appetizers.  Taste of Home [2] offers 39 amazing ways to grill fruit.

If you haven’t grilled fruits and vegetables, do give it a try. You will find them tasty, nutritious and a great way to enjoy those foods that are so good for you. Enjoy your grill even more by getting additional Get Fired Up! tips for grilling meat and baking.

This blog was reviewed by Anirudh Naig, Associate Professor in Hospitality Management & State Extension Specialist for Retail Food Safety at Iowa State University.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

More Posts

AnswerLine

Subscribe to AnswerLine Blog

Enter your email address:

Connect with us!

AnswerLine's Facebook page AnswerLine's Twitter account AnswerLine's Pinterest page
Email: answer@iastate.edu
Phone: (Monday-Friday, 9 am-noon; 1-4 pm)
 1-800-262-3804 (in Iowa)
 1-800-854-1678 (in Minnesota)

Archives

Categories