Q. A reader comments: In your column of July 9, you discussed methods of stabilizing whipped cream to a thick, durable foam. There is another alternative: Dr. Oetker's Sahnesteiff (cream stiffener). It comes in premeasured packets which you simply beat into the cream. It is available at the German Deli, 814 11th Street NW.

A. Dr. Oetker is a popular brand name in West Germany. Sahnesteiff contains dextrose, precooked edible starch and calcium phosphate. Dextrose is glucose, a simple sugar. Precooked starch, unlike the usual corn, potato or rice starch, does not need heat to thicken. Calcium phosphate acts as an emulsifier by buffering the acidity of the cream, thereby prolonging its life.

Sahnesteiff does a surprisingly effective job. First you whip 1 cup of cream for 30 seconds, then add the contents of 1 package. Almost immediately, the cream becomes stiff. You may notice a sharp bite at first: that's the calcium phosphate, which is acidic. It disappears quickly as it blends with the cream.

You can then add additional powdered sugar and flavorings. It's a good idea to reduce the speed of the mixer while adding the powder. Otherwise your kitchen will look like Christmas in June.

Q. I had a heavenly tea in the Pump Room in Bath, England. I have since mastered making scones but lack the clotted cream to smear on them. I've read many times that cre me fraiche is an excellent substitute. But I've never been able to produce it even though I've followed instructions exactly. Any suggestions?

A. Clotted cream is a specialty of western England, where great pans of milk are heated and skimmed. It is actually a mixture of butterfat and whey proteins that float to the surface, where the proteins coagulate and make it thick. Cre'me fraiche, which is similar in thickness but not in flavor, thickens due to lactic acid production by a bacterial culture. The acid causes the proteins to form a gel.

Cre me fraiche used to be thickened by naturally occurring bacteria. But now most cream is pasteurized, so a culture is added to set it. To make cre me fraiche, add 1 teaspoon buttermilk or yogurt per cup of whipping cream and set in a warm place overnight or until thick.

You cannot make cre me fraiche with UHT (ultra-pasteurized) whipping cream. UHT cream is so brutally heated that its proteins can no longer form a gel. Look for whipping cream that has not been ultra-pasteurized, such as High's or Green Springs brands.

If this cream also refuses to set, add 1 to 4 tablepoons nonfat dry milk to the cream and yogurt and mix thoroughly. The additional protein will give the cream more body.

Q. For many months I have been trying to get information on how to pickle potatoes. I haven't found anything on the subject and am perplexed and frustrated. Can potatoes be pickled?

A. You haven't found information because potatoes make very boring pickles. Think about all the pickles you've eaten. They were usually made with cucumbers, radishes, cabbage, onions, carrots, celery, mushrooms and so on. All these vegetables have flavors of their own, contain cellulose (which keeps them from falling apart) and look interesting when diced, sliced or whole.

Potatoes, on the other hand, have very little cellulose. They are very starchy so, if hot-packed, they would turn gummy. If fermented in a brine, they would disintegrate.

But don't let me stop you. Find a couple of pickle recipes, substitute potatoes and judge for yourself.

Q. With certain Oriental dishes, such as moo goo gai pan, the recipe calls for the addition of an egg white-cornstarch mixture to the cut-up chicken, which is then left to stand. But when it is turned into the hot oil, the egg curdles. Why does the egg white curdle? What is its purpose?

A. The egg white should not curdle. It should -- with the cornstarch -- form a white, velvety coating around each piece of chicken. You are either using too much egg white (the usual proportions are 1 white plus 1 1/2 tablespoons cornstarch per 100 grams ( 1/2 cup) thinly cut chicken breast meat) or you are letting the mixture stand too long. If it stands too long, water will exude from the meat and dilute the coating.