We’ve published hundreds of clever readers’ tips over the years, and every so often, we encounter one that makes us wonder, why does it work? We figured there must be a scientific explanation; after all, science lurks beneath everything we cooks do in the kitchen. So we rounded up some tips we’d been wondering about and turned them over to chemist and food science writer Robert L. Wolke, author of the two-book series What Einstein Told His Cook, for an explanation. Here’s what he has to say about the science behind the tips.
A better way to store herbs
Why it works
As any elated recipient of a floral bouquet knows, the best way to sustain the flowers—and the sentiment behind them—is to immerse the tips of their stems in water. The same is true for fresh herbs.
Many flowering plants and herbs (the socalled vascular plants) have bundles of elongated structures called xylem and phloem running up their stems to carry water and nutrients to the plants’ upper regions. When you put the stems of fresh herbs into water, the water rises through these tubes into the leaves and keeps them firm. Placing the herb bouquet in the refrigerator slows decay, so the herbs will stay fresh for as long as two weeks. Replace the water every couple of days so that bacteria and molds don’t take up residence in it.
Fighting onion tears
Why it works
Ask almost any cook and you’ll hear his or her pet strategy for preventing tears when cutting onions. “Cut them under water,” some will say, leaving open the question of whether the onions or the cook, or both, are to be submerged. Others may say, “Cut off the root end last,” as if the onion will know the difference and behave accordingly. And then there’s the last-line-of-defense school: Let the irritating gas spread at will, but protect the eyes and nose with a skin-diving mask—a technique I have used with success. (A Speedo bathing suit is not required.)
But before I tell you another, less clumsy, defensive measure, let me explain why onions make us cry.
The tear-producing gas is a chemical called (among other names) thiopropanal sulfoxide. It doesn’t exist in whole, intact onions. Instead, it forms at the time of cutting, when an enzyme (alliinase) and certain other chemicals (sulfoxides) escape from the broken cells and react with one another in the air to form the thiopropanal sulfoxide vapor. When this vapor reaches the eyes, it dissolves in our alwayspresent film of tears. This irritation stimulates the tear glands to try to wash the offending substance away.
All right, then, can anything eliminate or at least reduce the tears? Try this: Refrigerate your onion for an hour or two before you cut it. All chemical reactions, including the ones that produce onion tear gas, slow down at lower temperatures. If the onion is cold, there will be less gas and fewer tears.
But if you prefer to stick with some other pet method, that’s fine, too. If it works for you, go for it.
Make your own buttermilk
Why it works
In a pinch, this trick will work, but, as I’ll explain, it’s not always the best course of action. Adding an acid like vinegar (acetic acid) or lemon juice (citric acid) to milk curdles the proteins and makes the milk taste sour. But soured milk and buttermilk aren’t the same thing. Real buttermilk is cultured by adding live lactobacillus to milk. These bacteria feed on lactose, a milk sugar, and produce lactic acid, which partially coagulates and thickens the milk and also gives it a distinctive, tangy flavor. Milk that’s been soured with vinegar or lemon juice, however, tastes like, well, vinegar or lemon juice.
You can easily substitute soured milk for buttermilk in a recipe where the buttermilk’s primary function is a chemical one: for example, in a cake batter where the buttermilk is the acid that reacts with the baking soda and creates the carbon dioxide gas that helps the cake rise. But in recipes for buttermilk biscuits or pancakes or salad dressing—that is, any recipe where buttermilk’s unique lactic-acid flavor and consistency is key—only the real thing will do.
Soften brown sugar in the microwave
Why it works
This is a classic tip—at least since microwaves invaded our kitchens. Brown sugar consists of sugar grains, pretty much like the granulated sugar in your sugar bowl, but with the addition of a small amount of molasses. When exposed to air, the molasses dries and hardens, cementing the grains together into a block of sweet concrete. Heat from the microwaves softens the molasses cement long enough for you to measure out the sugar, but it will harden again as it cools.
A more permanent fix is to restore the brown sugar’s lost moisture by sealing it in an airtight container along with a wedge of apple or a piece of dampened paper towel (keep a sheet of plastic wrap or aluminum foil between the towel or apple and the sugar). The molasses will soften over a period of several days as moisture from the fruit or damp paper raises the humidity in the container
Thaw food quickly without gimmicks
Why it works
This is a great tip, and people are often astounded at how well it works. But heating the pan with hot water isn’t even necessary. You can thaw frozen food quickly simply by placing it on a heavy metal surface at room temperature. This works because metals very efficiently conduct heat from the surrounding air into the food. The heavier the pan, the more heat it can conduct, and the faster the food will defrost.
Copper and aluminum are the best heat conductors, but if a solid copper or heavy aluminum pan isn’t handy, a heavy stainless-steel pan with a thick copper or aluminum core will work very well. A cast-iron pan would be the next best option. A solid stainless-steel pan isn’t a great choice because stainless steel doesn’t conduct heat as well as the other metals. And a nonstick pan is even worse because its Teflon lining is a heat insulator—but there’s nothing to prevent you from using it upside down.