Category: Food Science

Preserving by Home Freeze Drying

Marlene Geiger

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 a more recent option for home food preservation due to the advent of home freeze dry units. HarvestRight, a company in Salt Lake City, Utah, introduced a freeze drying unit for home use in 2018, opening new opportunities for home food preservation. Early in 2023, a second company, Prep4Life, introduced a slightly different freeze drying unit for home use known as THE CUBE; Prep4Life is also a Utah-based company.

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 battlefield.  In the 1950s–1960s, freeze drying was viewed as a multi-purpose tool for pharmaceuticals and food processing and became a major component of space and military rations. Freeze drying has been widely used in the food industry for some time to extend the shelf-life of food while maintaining quality (think berries in commercial cereals that feature real berries) and offer consumers fast meal prep, emergency preparedness, and portable food. Freeze-dried foods also offer convenience as some foods can be eaten “as is” (except for raw meat, poultry, seafood, and eggs), added directly to recipes, or rehydrated and used as fresh food.

In a nutshell, freeze drying works by dropping the product temperature to <-40F, then reducing the pressure and adding heat to allow the frozen water in the product to change directly to a vapor (sublimate). Per HarvestRight, the process removes 98-99 percent of the moisture in food yet retains 97 percent of the nutrients, natural enzymes, and original flavor and color, making it a superior method for preserving food [1]. Additionally, freeze-dried foods are easy to use; food returns 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 10-pound bag of fresh apples weighs about one pound after freeze drying. Further, freeze dried foods supposedly have a 25-year shelf-life under proper storage conditions.

To date, very little university research has been done on in-home freeze drying; specifically research on how long the food retains quality and nutritive characteristics [3]. Utah State Extension staff has been experimenting with the HarvestRight dryers. In a recent webinar, they stressed that freeze drying produces high quality foods that are safe as long as they are handled properly prior to freeze drying, dried thoroughly, packaged appropriately, and used or prepared correctly 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.

Nearly any food item can be freeze dried—fruits, vegetables, herbs, meats (cooked and raw), eggs, dairy, meals, casseroles, desserts. Utah State recommends that vegetables be blanched prior to freeze drying to prevent discoloration. Food high in fat content, high in sugar content, and baked goods such as breads, cakes, muffins, etc do not freeze dry well and should be avoided. Sugar causes foods to expand.

To ensure the safety and quality of freeze-dried foods, basic food safety principles must be used in preparation, product must be completely dried (crisp), and product must be stored properly. Proper packaging is crucial to extend the shelf life of freeze-dried foods and prevent contamination or spoilage. The storage container must eliminate oxygen, light, and moisture. In order of long-term to short-term storage, the following containers may be used: Mylar® bags, vacuum-sealed canning jars, #10 cans, vacuum sealed bags, and PETE re-sealable containers. An oxygen absorber must be enclosed in the container to remove or decrease the available oxygen in the package to help maintain product safety, quality, and extend shelf life. Foods should be stored in a cool, dark place. 

For long-term storage, PET or PETE (Polyethylene terephthalate) food grade, non-toxic plastic pouches, also known as “mylar bags” are excellent. The opaque (silver) 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® bags with a clear side are not long-term air tight [3]. Mason canning jars can be used if they are vacuum sealed with a vacuum sealing machine capable of using a jar sealing device. Metal cans have a zero oxygen transfer rate and are great for long-term storage [4]. However, a #10 can contains a large amount of dried food which must be used at the time of opening or resealed in another container. Vacuum bags and re-sealable containers have short-term oxygen barrier qualities. 

Oxygen absorbers do not have a long shelf life; as soon as they are exposed to air (oxygen), they start to absorb and are spent when they become hard. They are available in different sizes (measured in cc’s); contents and container size should be considered when purchasing absorbers. The smaller the container the less cc’s needed. There is no harm in using a larger than needed absorber and would be preferred to one that is too small [3]. When a container is opened, the absorber should be replaced before resealing.

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 food [5]. While dehydration is a very acceptable means of food preservation, it differs from freeze drying in several ways: 
– foods shrink up and develop a leathery feel and appearance;
– foods do not return to their natural state;  
– foods retain less of their nutritional value;
– foods have a 4 months to 1 year shelf life;   
– fewer foods are successfully dehydrated;
– foods rehydrate slowly.

There are many advantages to freeze drying. Besides holding nutritive value, it allows one to utilize garden produce at the peak of harvest, buy in bulk, save money over commercially prepared freeze-dried foods, offers a long shelf life, preserve foods that cannot be typically preserved, and offers compact, lightweight storage. Some disadvantages pointed out by Utah State Extension include unit size, noise, time for drying and allowing freezer to unthaw, cleaning, sanitation, and maintenance, small batch sizes, and cost—cost of the machine as well as machine accessories, packaging supplies, sealers [10], and electricity. In addition, reconstituting freeze-dried foods is somewhat experimental. Utah State Extension specialists suggest starting with a small amount of water and giving ample time to reabsorb; there is no need to rehydrate herbs, onions, or bell peppers as they can be added directly to foods and will absorb moisture from the food. Buying a Home Freeze-Dryer: What to Know Before You Go and Let’s Preserve:  Freeze Drying offer more information.  

The options for food preservation are many. Each method offers pros and cons to preservation and storage. If long-term food storage or portable food storage is the goal, freeze-drying is an option to consider. HarvestRight machines are available at several retail outlets. The Cube is available from the Prep4Life company. Imagine rehydrating lasagna on a camping trip!

Sources:

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.

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Small-Batch Fermentation – AnswerLine Team Gives It a Try

Marlene Geiger 2 Comments

In recent years, consumers have become more interested in home fermentation, especially in making their own sauerkraut and kimchi for the beneficial bacteria it provides for gut health.  As this trend grows, the AnswerLine team receives many questions about the fermenting process. To help answer questions with first-hand experience, the AnswerLine team rolled up their sleeves and spent an evening learning to create the digestive ‘wonder food,’ sauerkraut, from scratch.

The biggest trend in DIY sauerkraut and kimchi is making it in small batches—small amounts made regularly using quart, half-gallon or gallon jars. Kraut or kimchi made in small batches ferments more quickly than in big crocks allowing one batch to be fermenting while another is refrigerated and eaten. The market has responded to consumer demand by providing consumers with a large assortment of fermentation kits, containers, and gadgets to make fermentation easy and fun.  The AnswerLine team randomly chose two different kits with which to experiment—MasonTops® and Ball®—to ferment cabbage into sauerkraut. Both of these kits used quart jars which were prepared in advanced.

Mature, firm heads of cabbage were selected from a team-member’s garden a day prior; cabbage can also be purchased at the supermarket for year-round kraut making.  Both red and green cabbage varieties can be used; the team used a mix of red and green.

We used a mandolin to shred the cabbage. Cabbage can also be shredded using a sharp knife, kraut cutter, or food processor.  However cut, the shreds should be long and thin.  Once the cabbage was shredded, it was weighed, and salt (canning and pickling salt) added per the kit recipe.

The salt was massaged into the cabbage until the cabbage was wilted and juicy. 

The wilted/juiced cabbage was firmly packed into the quart jars allowing the juice to come to the top and completely cover the cabbage. 

The two kits allowed for different amounts of headspace.  What is most important is that there is sufficient headspace for the brine from the cabbage/salt mix to completely cover the top of the cabbage.  After the jars were filled, the jars were weighted and topped with the fermenting lid and screw band supplied with each kit.  Weights can be a food grade glass disk (provided with the MasonTop® kit), stainless steel spring (provided with the Ball® kit), a freezer bag filled with brine* that fits into the jar, a smaller glass jar filled with water or brine, or a full wine bottle that sits on top of the cabbage.  If using a brine bag, glass jar, or wine bottle for weight, whole cabbage leaves (discard when the kraut is done fermenting) should be packed atop the cabbage first.

Rachel Sweeney and Thomas, Marlene Geiger, Beth Marrs, Marcia Steed, and Carol Van Waardhuizzen show the jars of cabbage ready for fermenting.

Each team member left the workshop with two jars to ferment at home.  At home, team members were advised to store their jars in a cooler, darker place in their home, to check it daily to make sure that the cabbage was always covered in brine, and to wait about 2 weeks to test.  Fermentation time is dependent on quantity and temperature.  Kraut fermented at 70º-75ºF will ferment in about 1-2 weeks; at 60º-65ºF, fermentation may take 2-3 weeks.  At temperatures lower than 60ºF, kraut may not ferment and above 75ºF, kraut may become soft or mushy.  The best way to determine when the kraut is ready is by smell and taste.  The cabbage should be translucent but remain crunchy, not soft or slimy. The salty flavor should be diminished and replaced with a bright, tangy flavor of the lactic acid. When the kraut has reached an individual liking, it is time to stop the fermentation by refrigerating and eating it.

Here are the team takeaways from this experience:

  • Small batch kits make it easy to get started, learn about the fermentation process, and build fermentation confidence. Kits are a matter of personal preference.
  • Approximately 2 pounds of cabbage is needed to fill a quart jar.
  • Tightly packing the cabbage into the jars is important to continue releasing the juices necessary to create the anaerobic (without oxygen) environment need for lacto-fermentation to take place while inhibiting spoil-causing bacteria.
  • Work in small batches when packing the cabbage into the jars.  Pack tightly after each handful addition.
  • Important to keep oxygen out yet allow carbon dioxide to bubble out.  Good amount of brine, weight, and lid with an air release enable this. 
  • Keep the cabbage submerged under the brine at all times to prevent oxidation; cabbage will brown at the top if the brine level drops. Add brine during the fermentation time, if needed.
  • Monitor it daily watching for off smell or loss of brine.  Watch for signs of healthy fermentation: cabbage swelling, gas pockets, color changes, bubbles or foam on the surface of the brine, some white sediment in the bottom of the jar. Bubbling activity is normal and a good sign the fermentation process is working.
  • Flavor improves with age but can be customized to individual taste and probiotic level. Longer ferments give a stronger flavor and more probiotics. 

Fermented foods can be a healthy and nutritious addition to your diet and a great way to preserve the harvest as well. Sauerkraut is one of the oldest and easiest of fermented food. Unlike the packaged kraut at the supermarket which may have been pasteurized to kill bacteria, small-batch sauerkraut is lacto-fermented, a fancy term for soaking uncooked cabbage in brine (salt and water), then letting nature ferment the vegetable’s own beneficial bacteria.  This process was perfected by the Germans during the 16th century and still used today.   (While the Germans are best known for their kraut making skills, it is believed that the first sauerkraut was made in China about 2,000 years ago, during the building of the Great Wall.)   

For recipes and additional information or help, check out Small Batch Sauerkraut Tips and Sauerkraut:  Problems and Solutions by Oregon State University Extension. 

Taking the plunge into home fermentation can be an intimidating proposition. Whether you’re a complete beginner or have some experience, small-bath fermentation with cabbage is a good place to start to build your confidence while learning about fermentation.

____________________________________

*Brine – ½ teaspoon salt to ½ cup water

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.

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Sweet Fruit Spreads – The Science of Successful Gelling

Marlene Geiger

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.

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