The Problem of Temperature

• Making candy at home is a fascinating hobby, but it can be maddeningly unpredictable as well. Weather conditions, impurities in the sugar and variations in cooking temperature can all leave enthusiasts scrambling to salvage a misbehaving batch. Imprecise temperature control is one of the biggest problems. Old recipes instruct cooks to dribble a small amount of candy into a glass of cold water, and observe the result. For example, sugar at the hard-ball stage forms balls up into a hard nugget of sugar, while syrup at the soft crack stage -- a few degrees higher -- forms firm but bendable strands with a chewy texture. You can manage good results with time and practice, but it's easier to purchase a good thermometer.

Your New Best Friend

• If your life won't feel complete until you've mastered sponge candy, a good thermometer can be your best friend. Candy thermometers, which sometimes double as deep-fry thermometers, come in two primary versions. One is a glass tube with temperatures marked on inside of the glass, and the other is a metal probe with a dial or LED display at the top. Both types attach to the side of your pot, so you can monitor the temperature of your sugar as it cooks. Bear in mind that most thermometers lag slightly behind the real temperature of your sugar, so your candy is done slightly before the thermometer reaches the appropriate temperature.

Cooking Your Sponge Candy

• Sponge candy is made almost entirely of sugar boiled in water, with a small amount of corn syrup and vinegar added. The corn syrup and vinegar both help prevent your candy from crystallizing, as water evaporates and the concentration of sugar in your syrup rises. The less water it contains the higher the temperature can go, which gives a very accurate measure of the sugar's concentration. Simmer your candy in a large pot until it reaches a temperature of at least 295 Fahrenheit, and preferably 300 to 302 F. Add the baking soda to your candy, which will foam briefly to three or four times its natural volume. Whisk it in for 10 seconds or so, then pour it into a greased or parchment-lined pan to cool.

A Few Tips

• It's important to use a much larger pot than you think is necessary, to allow for that explosive increase in volume from the baking soda. If your pot spills over it will make a serious mess, and can cause serious burns if you're unfortunate enough to get any on your hands. A thin layer of hard candy will form at the top and bottom of your sponge. Cut that away with a sharp knife, leaving just the airy middle layer. That can be eaten as is, but in Buffalo, N.Y., where sponge candy is considered a local specialty, it's usually dipped in chocolate. This seals it against moisture, protecting the candy's delicate crunch.