- The Washington Times - Tuesday, February 20, 2007

It can occur in many a good recipe when you least expect it: Rice or potatoes simply will not cook through.

My friend Debbie Bickford cooked arroz con pollo — chicken, crushed tomatoes and rice. After 1-1/2 hours, the rice was still hard and uncooked.

In one of their packet meals, Reynolds Wrap home economists Pat and Betty ended up with potato pieces that should have cooked in 10 minutes but remained raw after more than an hour.

In an Italian restaurant the other night, my husband, Arch, and I were served a side dish of provolone and mozzarella cheese covering soft layers of tomatoes and onions. At the bottom was a layer of thinly sliced, rock-hard raw potatoes.

Why didn’t the rice and potatoes cook through? Normally, when heated in liquid, starch granules in rice and potatoes swell and soften, but if the starch is cooked in an acidic environment, it cannot swell.

The acidic tomatoes had prevented the starch in my friend Debbie’s rice from swelling, so it remained rock hard. Pat and Betty had added a few tablespoons of vinaigrette to season the potato packet they were making. The vinaigrette was acidic enough to prevent the starch in the potatoes from swelling and softening.

The acidity from the tomatoes in the restaurant side dish my husband and I ordered prevented the starch in the potatoes from cooking through.

Just to confuse matters, not only does too much acidity prevent starchy foods from cooking through, too little acidity can also prevent it. For example, proteins, such as those in eggs and flour, need a minimum acidity to bond and cook.

Recently, I made a flourless cake for a new book I am working on. This was to be a chocolate flourless cake containing semisweet chocolate and lots of eggs. Many recipes also include a stick of butter, although I didn’t on the first try. The cake was beautiful, perfectly level, but when I took a bite, it was as dry as chalk.

I should have known it would be dry because of all the egg whites I used. Egg whites are major drying agents. For my revised version, I was planning to cut some of the eggs, or at least some of the egg whites, but I decided to try substituting an equal amount of heavy whipping cream for the butter.

I guessed wrong. With cream in place of butter, my dry cake became pudding. What happened? Butter is generally 80 percent fat, with about 16 to 18 percent water and only a tiny amount of dairy solids. However, cream and milk, which have a lot of dairy solids, contain buffers — compounds that grab acidity or alkalinity to keep the cream and milk from changing.

So when added to my recipe, the cream had stolen the acidity of the semisweet chocolate, leaving the batter no longer acidic enough for the eggs to set.

I frequently get queries from chefs using Dutch-process cocoa, which is alkaline. A chef in California called asking about a biscotti recipe that failed. She was not a novice cook and she told me she had made this particular biscotti many times.

Someone had given her a good Dutch-process cocoa that she decided to use. She was so sure of her recipe that she did not even look in the oven until it was time to take out the loaves. To her astonishment, instead of two loaves, she found a big chocolate puddle. The Dutch-process cocoa had made the batter so alkaline it would not set.

Several years ago, baking expert Susan Purdy, who was working on her high-altitude cookbook, “Pie in the Sky” (Morrow), called from 9,000 feet to tell me that all of her recipes had worked fine except for a chocolate cake. I responded, “You’re using Dutch-process cocoa.” “How did you know?” she asked.

At high altitude, cakes must set fast before they lose their leavening.

Miss Purdy needed all the acidity she could get to make the batter set quickly, and the alkaline Dutch-process cocoa was disastrous.

Alas, too much acidity can prevent starches such as potatoes and rice from setting and too little acidity can prevent the proteins in eggs and flour from setting. In either case, too much or too little acidity can wreck a dish.

To deal with failed dishes in which Dutch-process cocoa was used, simply switching to natural cocoa may solve the problem. With other recipes, remember that dairy products contain buffers and may rob your dish of acidity.

So getting rid of the dairy product or switching to an acidic dairy product, such as buttermilk or sour cream, may take care of the issue. In some cases, adding something acidic, such as cream of tartar, may help.

In the case of ingredients with starch that doesn’t cook, such as potatoes or rice, try cooking the starchy ingredient first in water or chicken stock and then putting it together with the acidic ingredients.

This is what I have done in the potato dish that follows. Try it and see what you think.

A hint of Italy potato casserole

Herbs, onions and tomatoes make this bubbly cheese-topped potato dish a family favorite. You can cook the potatoes and onions, assemble the dish ahead, then bake and serve. Since the acidity from the tomatoes will prevent the starch in the potatoes from swelling and softening, it is essential to cook the potatoes before baking.

4 medium Yukon Gold potatoes, peeled and sliced 1/4 inch thick

Water

1 teaspoon sea salt

6 tablespoons olive oil, divided

1 teaspoon fresh rosemary, chopped

2 medium onions, thinly sliced

3 ripe medium tomatoes, sliced

1 tablespoon fresh oregano leaves

1½ cups grated mixed provolone and mozzarella cheeses

In a medium saucepan, cook potato slices in a large amount of water with sea salt until tender enough for a fork to pierce them easily. Drain.

Pour 3 tablespoons olive oil into a large skillet. Add rosemary and heat over low to medium heat. Add potatoes and toss gently to coat with rosemary and oil. Pour into a 9-by-13-inch casserole. Wipe out skillet, add 2 tablespoons olive oil and saute onion over low to medium heat until soft, about 10 minutes.

Layer onion on top of potatoes. Gently toss tomato slices with 1 tablespoon olive oil and oregano, and then layer on top of onion. Cover with grated cheese.

Place on shelf slightly below middle of preheated 350-degree oven and bake for about 30 minutes, or until casserole is heated through and cheese is bubbly and browned.

Makes about 6 servings.

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