A recent caller reported a mysterious incident with butternut squash soup, which she typically cooks in 3-gallon batches. This time, she altered her normal recipe, adding a handful of brown basmati rice to use as a thickener. After cooking, she cooled the soup overnight on her chilly back porch. The next day, she discovered that the soup was alarmingly tangy, with a strangely fermented flavor reminiscent of alcohol. What happened?
It’s no coincidence that the butternut squash soup had fermented, alcoholic notes. Indeed, fermented rice turns out to be the culprit here. Rice is high in starch, which is relatively easy to ferment. And when rice ferments, it produces alcohol, along with many of the same flavor molecules created during the production of sake (a wine made from fermented rice). When dealing with leftovers, it’s important to be mindful of the storage temperature “danger zone.” This is a temperature range between 40°F and 140°F, within which bacteria grow most easily. In this case, the porch likely was not cold enough to prevent bacterial growth. To make matters worse, in a 3-gallon pot, hot soup cools slowly, giving bacteria ample opportunity to multiply. To prevent this kind of fermentation (or other bacterial growth) in leftovers, it’s best to transfer the food to smaller containers before putting them in the refrigerator—or any other cold, temperature-controlled environment. This allows the food to cool faster and stay at a temperature that prevents bacterial growth.
Spilling the Beans
When it comes to cooking dried beans, there’s a lot of contradictory advice out there about when to salt them. For instance, is it best to add salt to the beans as they soak or as they cook—or both? Frustrated caller Judy Kostura, of Austin, Texas, wanted a definitive answer.
Salt plays a major role in the texture—and flavor—of cooked beans. That’s because the sodium ions in the salted water affect the cell walls of the beans’ skins, helping to dissolve pectins (the soluble fiber found in plants) from the cell walls and allowing water to more easily penetrate the beans’ tough exteriors. We tested kidney beans, experimenting with different combinations of adding salt—or not—during soaking and cooking. We found that beans that were soaked and cooked without salt had tough, chewy skins and a chalky, firm interior. By comparison, beans that had been soaked in salted water were far more tender. But the best beans by far turned out to be the ones that were both soaked and cooked in salted water. This produced the most flavorful beans, which also had the creamiest texture and the softest skins yet still held their shape well. To cook 1 pound of dried beans, we recommend soaking them in 2 quarts water with 1 tablespoon kosher salt. After soaking, drain them and cook in 6 cups water with 1½ teaspoons salt.
When following a recipe that called for simmering potatoes in a tomato-based sauce, Jen Plumb, of Seattle, discovered that her potatoes would not tenderize, no matter how long she cooked them. She wondered if the acidic tomato sauce might be to blame.
Plumb was onto something: It’s all about the acid. Potatoes—like other vegetables—contain plenty of pectin, a structural fiber found in the cell walls of plants. Pectin remains stable when in contact with acid, be it from tomatoes, lemon juice, vinegar or wine. During cooking, the acid strengthens the pectin, preventing vegetables from tenderizing when heated. (Conversely, vegetables cooked in an overly alkaline liquid quickly become mushy.) We tested the effect of acid on potatoes by boiling potato slices in two types of acid: vinegar and lemon juice (or acetic acid and citric acid, respectively). In each case, it produced tough, rubbery potatoes with a gelatinous inner texture—an effect that was especially pronounced when using lemon juice, which has a slightly lower pH than vinegar, meaning that it’s more acidic. We also found that waxy gold potatoes turned out even tougher and more rubbery than floury russets. In some dishes where firmer vegetables are desirable, acids can be used to ensure they have a bit of “snap” to them. For example, some cooks prefer the way green beans stay relatively firm when cooked in a tomato-based minestrone. But in general, it’s good to add acidic ingredients after potatoes have been cooked to the desired doneness. Or, for recipes with tomato-based sauces, a better approach might be to cook the potatoes separately, then stir them in at the end for the ideal texture.