Even professional cooks sometimes have trouble gauging when strawberry jam is the right consistency. A successful jam depends on the proper balance between acid, sugar and pectin, a natural substance that is extracted from most fruits when they are boiled. Too little pectin makes jams runny, while too much makes them unpleasantly thick.

Some fruits, like apples, grapes and currants, are rich enough in pectin and can jell easily. But strawberries have a low pectin content, and like other fruits lose pectin when they ripen.To compensate, some cooks recommend making jam with one-third underripe strawberries, for pectin, and the rest ripe strawberries, for flavor. In some recipes, strawberries are combined with a high-pectin fruit, and other recipes may call for commercial pectin, available in supermarkets.

To determine if the mixture is done, drop a large spoonful of the jam onto a saucer that has been put in the freezer. In two minutes, the jam should set at the consistency the batch will be when cooled.

Another method is to use a candy thermometer. The jell point, the temperature at which the mixture has thickened properly, is 220 degrees for jelly and a degree or two higher for jam.

No matter the method you use, if the jam is not thick enough, some cookbooks suggest continuing to cook it with the addition of a couple of underripe tart apples that have been peeled, cored and thinly sliced. The apples will yield pectin without compromising the strawberry flavor. Remove the apples when the jell point is reached or the jam passes the freezer test.

If the jam is too thick, stir in water a tablespoon at a time until you have reached the proper consistency.

Remember, too, that jam thickens as it cools, so what is in the pot should be a little runny when you remove it from the heat.

- Linda Amster