Why? Why do potatoes get gluey, won't cream whip, does jelly not set?

Sunset, Dec, 1992 by Linda Lau Anusasananan

Why do some of the simplest cooking tasks occasionally produce bizarre results? It could be because you use a different tool or technique--one that seems like it should produce the same results, but in fact radically changes the end product. Here we give three such cases.

If you've encountered similar kitchen mysteries and would like solutions, send your questions to Why?, Sunset Magazine, 80 Willow Rd., Menlo Park, Calif. 94025.

For help in unraveling culinary puzzles, we call on Dr. George York, extension food technologist at UC Davis's Department of Food Science and Technology.

Why do potatoes get gluey if you mash them in a food processor?

When the food processor was new, mashing potatoes was one of the first things many of us tried to do with it. After all, an electric mixer does the job well, and a food processor should do it easier and better. Right? Wrong.

The reason has to do with the starch in potatoes--it's distributed in structures called starch buds (also called starch grains or starch granules). In a food processor or blender, the blade is so fast and forceful, it cuts open the buds, allowing the gluey starch to leak out.

Why doesn't this happen when you break up potatoes with a masher or electric mixer? Because these tools aren't forceful enough to break the starch buds by the time the potatoes are fluffy and ready to eat. But if you keep on mashing or mixing, you can make any potato gummy.

In thin-skinned potatoes, the structure that holds the starch buds together is fragile, making buds easy to break; these potatoes are not good mashers. Russet potatoes mash best because their large starch buds tend to separate easily from each other rather than break.

Why doesn't whipping cream always whip?

It's the fat emulsified in cream that allows it to whip and stay whipped. As you beat, tiny fat globules suspended in liquid stretch around air bubbles whipped into cream and hold them for several hours. Given sufficient agitation, milk with as little as 3 1/2 percent fat will get quite foamy, but the foam rapidly fizzles because there is not enough fat to sustain it.

Heavy whipping cream (36 to 40 percent fat) whips most readily, and at best can double in volume (depending on which whipping tool you use). Richer cream won't hold as much air. Light whipping cream (the kind most available, and usually labeled just "whipping cream") has less fat--a minimum of 30 and up to 36 percent--but whips satisfactorily.

To whip well, cream must be cold (35|degrees~ to 45|degrees~). If it's warmer, the fat globules in the cream are so soft that as the whipping action takes place, they run together rather than stretch. You get either no foam or a curdled mess. If the bowl and beaters are chilled, they help cream stay cold while it develops good volume.

The shape of the beater or whipping utensil also affects the amount of air beaten into the cream. A food processor (or blender) with a metal blade pulls in little air, producing a dense, thick foam with little volume; the process is also so fast you can easily end up with butter instead of whipped cream.

Balloon-shaped whips (with multiple wires) and electric or rotary beaters do the best job of incorporating air into cream for the lightest, fluffiest results.

For stiffest foams, whip the cream by itself. Stir in sugar or flavorings last.

Cream beaten to hold distinct peaks stays whipped longer than softly whipped cream. But if you softly whip cream ahead and chill it, covered, until ready to use, you can perk up its texture with a few last-minute whisks.

Why won't jelly jell when you multiply the recipe?

Pectin, which makes jelly set, is heat sensitive. This is particularly true of pectin sold for home jelly making.

If you multiply ingredients for a jelly recipe, you're asking for trouble. The mixture must cook longer than the recipe (or pectin) is designed for, and the pectin in the bottom of the pan stays hot long enough to lose its jelling properties before the top of the mixture reaches the jell point. This is why directions that come with pectin should be followed exactly.

Then how do commercial makers cook large batches? They use steam-jacketed kettles, which bring heat uniformly and quickly to all sides of the containers.