On the Jelling of Jelly

Making jams and jellies is becoming a lost art in many parts of the country. Not in Alaska! Our array of tasty wild berries brings out the berry pickers as well as the bears. Raspberries, blueberries, lingonberries, highbush cranberries, wild currants, cloudberries, and rose hips, not to mention the strawberries from our gardens, are transformed in quantity each year into spreads to put on next winter's toast.

The process of making jam or jelly involves a substance called pectin. Pectin is a carbohydrate, made up mostly of carbon, hydrogen, and oxygen. It is formed from substances found in the cell walls of fruit, and particularly concentrated in skins and cores. The conversion of these precursor substances to pectin occurs naturally during ripening, and can also be forced by long cooking, as in the traditional methods of making jellies without added pectin.

Fruits vary a great deal in how much pectin or pectin precursors are present. Raspberries and blueberries, for instance, are low in pectin, while apples, citrus fruits, cranberries, and currants are high. Pectin can be extracted from high-pectin fruits and added to low-pectin ones to make better jellies with less cooking. Commercial pectin today is usually extracted from the white inner part of citrus skins.

Pectin produces structure and a kind of stiffness in jellies and jams by forming a water-holding network within the juice or crushed fruit. Before jelling starts, individual molecules of pectin are surrounded and isolated from each other by water molecules. If the surrounding solution is acid enough, the pectin loses some of its attraction for these isolating water molecules. Sour fruit will normally provide enough acid to take care of this step. If the acid content of the fruit is low, lemon juice can be added to make the fruit mixture more acid.

Once the pectin has loosened its hold on the water molecules, something more attractive must pull the water away from the pectin. This is the role of sugar. Artificial sweeteners may affect taste, but they do not attract water as sugar does. This is why ordinary pectin cannot be used to make jellies without sugar.

With its water stripped away, pectin opens out into a structure which links readily with other pectin molecules to form a three dimensional network. This network is what gives the stiffness to the finished product.

So where does the cooking come in? Before the advent of commercial pectin, long cooking transformed the pectin precursors in the fruit into pectin. With added pectin, it is perfectly possible to make jam at room temperature. However, the heat of cooking speeds up the process of setting and also sterilizes the jam. Uncooked jams need about twenty-four hours at room temperature to jell, and they must be stored frozen if they are not used within a few weeks. Cooked jams and jellies, poured into sterile jars while still at the boiling point and covered at once with an airtight cover of paraffin, should keep as long as the seal is intact.

If the balance of acid, sugar, pectin and liquid isn't right, the network of pectin molecules may not form. If this happens, what's left will still make a good ice cream topping, but it isn't much use as a spread.