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Just-right fruits, veggies

Controlling how cooking alters texture

By Shirley O. Corriher TRIBUNE MEDIA SERVICES | Wednesday, January 7, 2009

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Cooking knowledge has been handed down generation to generation, so it should not be a surprise that errors are passed on as well. One such error is that acidic ingredients preserve the shape of food.

I have had three chefs tell me that acid preserves the shape of foods. Things like: "You should add vinegar to Boston baked beans to preserve the shape of the beans during the lengthy cooking."

This is absolutely not true. Acidic ingredients can prevent the cooking of starches -- keep them rock-hard raw and inedible. In Boston baked beans, thank goodness, most cooks do not add enough vinegar to cause this. The sugar and molasses actually are what cause the beans to retain their shape during hours of cooking.

In an effort to clarify this whole issue, let's go over foods and shape changes during cooking. Cooking methods and other ingredients can change the shape of food. Proteins become firmer with heat (for example, eggs go from liquid to solid) but fruits and vegetables soften with heat. Starches swell and soften.

Proteins: heat or acid

Raw natural proteins are separate individual units. Picture little individual wads of ribbon, each held together by bonds. You have a wad (raw protein) over to the left, one to the right -- they are totally separate, with plenty of room for light to go between them. You can see right through an egg white when you crack it in a pan. As you heat raw proteins, some of their bonds break, and the "wad" partially unwinds, with some of its bonds sticking out. Almost immediately, this partially unwound protein with its bonds exposed runs into another unwound protein, and they bind together. There is no longer room for light to go between. The egg white in the frying pan becomes solid white.

Acidic ingredients can "cook" raw proteins just like heat. Ceviches are raw fish or scallops that have been "cooked" with lime juice (the most acidic of citrus juices).

Fruits and vegetables: sugar or calcium

When you heat a fruit or vegetable, the cell walls shrink, and the cells start to leak. The complex pectic substances and hemicellulose glue between the cells change to water-soluble pectins and dissolve. The cells are leaking and falling apart. It's no wonder fruits and vegetables soften when we cook them.

In many desserts, you may want the fruit to soften but not fall apart. In an apple pie, you want nice apple wedges, not applesauce. In some legume dishes such as Boston baked beans, you want the beans to hold their shape -- not turn to bean mush like refried beans.