Getting Saucy with Starch

Cornstarch can be the secret to the perfect sauce—or it can create a gloppy mess. Our listeners asked for guidance for getting it right.

To create thick, glossy sauces, cornstarch first is mixed with a little water to create a slurry, which then is stirred into the sauce ingredients and heated (adding dry cornstarch to a warm liquid causes clumping). At 203°F to 212°F, the starch granules absorb liquid, thickening the sauce. The rule of thumb generally is to add cornstarch at a ratio of 1 tablespoon per 1 cup of water or broth. To test whether that really was ideal, we made three batches of gravy using 1, 1½ and 2 tablespoons cornstarch per cup of liquid. The 1-tablespoon version was pleasantly smooth, but a bit runny, while the 2-tablespoon mixture was gloppy. The 1½-tablespoon batch was the best choice, thickening to a desirable consistency without becoming lumpy or overly sticky. This ratio also proved the winner with our teriyaki sauce. For best results, the slurry should be gradually whisked into the hot liquid and brought to a simmer, stirring constantly. And if you prepare your slurry in advance, be sure to stir it again just before adding it to the sauce ingredients; the cornstarch and water will separate on standing.

Brownie Points

Cocoa powder and unsweetened chocolate often are called for in similar types of brownie recipes. Several listeners wondered how interchangeable they are and if there are reasons to use one or the other.

Cocoa powder and unsweetened chocolate are both sugarless and add intense chocolate flavor to baked goods, but they are quite different. Unsweetened chocolate is sold in bars made from cocoa solids and cocoa butter. Cocoa powder is made from pulverized cocoa solids from which much of the cocoa butter has been extracted. Unsweetened chocolate typically contains about 50 percent cocoa butter, while cocoa powders contain 10 to 25 percent cocoa butter. This can make a huge difference in how these products perform in baked goods. We tested each in brownies, substituting unsweetened chocolate in recipes developed to use cocoa powder and vice-versa, using equivalent gram weights of each ingredient. When subbed for cocoa powder, unsweetened chocolate produced oilier, stickier brownies that required longer baking thanks to the extra fat from the cocoa butter. When cocoa powder was used in a brownie recipe developed for unsweetened chocolate, the cocoa powder absorbed more liquid and produced a drier batter; the resulting brownies had an intense chocolate flavor that verged on acidic. And in a simple frosting test, we found that the extra cocoa butter in unsweetened chocolate translated to a smoother, more spreadable texture; by contrast, cocoa powder icings were thicker and slightly drier. Overall, we found that cocoa powder and unsweetened chocolate should not be used interchangeably without adjustments that take into consideration the recipe’s overall fat, liquid and sugar content.

Copper for Peak Perfection?

Copper bowls have long been touted as the best way to whip egg whites. Our listeners have asked whether that’s true. And, if so, are copper bowls a worthwhile investment?

Copper does possess unique properties that enhance the whipping of egg whites. While whisking, copper particles bond with the egg proteins, preventing the overly tight bonds that otherwise can cause lumpy textures—a common issue when egg whites are overwhipped—for fluffier, airier results. In our tests, egg whites whipped in a copper bowl were indeed airier and had finer bubbles compared to those whipped in a glass bowl. But copper bowls are costly and hard to source. Luckily, there’s another method for better egg white whipping: adding acid. Acids such as lemon juice or cream of tartar also reduce protein bonding. Using lemon juice (1 tablespoon per four egg whites) in a glass bowl resulted in glossy, firm egg whites that almost mirrored the results from the copper bowl. Using cream of tartar (½ teaspoon per four egg whites) produced slightly better results, yielding fluffy, stable peaks without the potential lemon juice drawback of adding extra liquid (which can throw off certain recipes). We also tested an old-school trick that combines both approaches—rubbing a cut lemon inside a copper bowl before whipping. While this did enhance the whipping efficiency, it also affected the appearance of the egg whites—they turned yellow, due to the interaction of lemon juice with copper. Ultimately, we found that while copper bowls are excellent for achieving lofty peaks in egg whites, for most home cooks, it’s easier and cheaper to simply add cream of tartar (our first choice) or lemon juice.