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.

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