Fruits contain essential vitamins, minerals, fiber and sugar. Aside from sugar giving fruits its flavor, it also contributes to the firmness, color, and mouthfeel.
- Jellies & Preserves
Sugar is essential in the gelling process of jams, preserves and jellies to obtain the desired consistency and firmness. This gel-forming process is called gelation—the fruit juices are enmeshed in a network of fibers. Pectin, a component of fruits, has the ability to form this gel only in the presence of sugar and acid. Sugar is essential because it attracts and holds water during the gelling process. In addition, acid must be present in the proper proportions. The optimum acidity is a pH between 2.8 and 3.5. Some recipes include lemon juice or citric acid to achieve this proper acidity.
The amount of gel-forming pectin in a fruit varies with the ripeness (less ripe fruit has more pectin) and the variety (apples, cranberries and grapes are considerably richer in pectin than cherries and strawberries). In the case of a fruit too low in pectin, some commercial pectin may be added to produce the gelling, especially in jellies. In recipes that use commercial pectin, the proportions of sugar may be slightly higher or lower than the one part fruit to one part sugar ratio.
Sugar prevents spoilage of jams, jellies, and preserves after the jar is opened. Properly prepared and packaged preserves and jellies are free from bacteria and yeast cells until the lid is opened and exposed to air. Once the jar is opened, sugar incapacitates any microorganisms by its ability to attract water. This is accomplished through osmosis (the process whereby water will flow from a weaker solution to a more concentrated solution when they are separated by a semi-permeable membrane). In the case of jellies and preserves, the water is withdrawn from these microorganisms toward the concentrated sugar syrup. The microorganisms become dehydrated and incapacitated, and are unable to multiply and bring about food spoilage. In jellies, jams and preserves, a concentrated sugar solution of at least 65% is necessary to perform this function. Since the sugar content is present in fruits and their juices is less than 65%, it is essential to add sugar to raise it to this concentration in jellies and preserves.
Sugar helps retain the color of the fruit through its capacity to attract and hold water. Sugar absorbs water more readily than other components, such as fruit, in preserves and jellies. Thus, sugar prevents the fruit from absorbing water, which would cause its color to fade through dilution.
Check out some of our fruit jam recipes that bring color to life below.
- Canning & Freezing Fruit
Fruit to be canned is placed in syrup of greater sugar concentration than that in the fruit itself. The dissolved sugar in the syrup diffuses into the fruit (osmosis) and improves its flavor. As the fruit cooks in the syrup, the cell walls become more permeable, the fruit texture grows tenderer, and the retention of sugar renders the fruit plump and attractive. Whole fruits with tough skins, such as kieffer pears and kumquats, are impermeable to the sugar syrup unless precooked or unless the skins are pierced.
Some fruits such as blueberries, cranberries, raspberries and rhubarb may be frozen in a dry pack without sugar, however these and all other fruits benefit greatly from a sugar pack regardless of the type used (dry or syrup). Sugar helps protect the surfaces of frozen fruit from contact with air, which produces enzymatic browning-discoloration due to oxidation. In some cases, such as with peaches, nectarines and apricots frozen in a syrup pack, ascorbic acid is also added to help prevent darkening. The presence of sugar also lessens flavor change by retarding possible fermentation. In addition, texture, fresh fruit aroma, and normal size are retained upon thawing when sugar is used in freezing fruit.