| 196 | 197 | 198 | 199 | 200 |
| 1 | 103 | 205 | 308 | 410 |
|
You may have seen the produce clerk at the supermarket removing covers from the
potato bins just as they open their doors early in the morning. The covers are not to keep the flies
off. At most supermarkets the overhead lights are on all night for the reshelving and for the
cleaning crew. Since light is deleterious to potatoes (and develops the poisonous solanine), a
well-informed produce manager covers the potatoes as long as there are no customers in the
store. The dark amber or rose-colored bags they often package potatoes in is to protect them
from strong light, too.
Sometimes when you cook or bake potatoes, you must have noticed that the ends turn
black. This is not toxic, just unappetizing, that heat causes. If you have similar problem with a
whole batch you just bought, acidify the cooking water by adding cream of tartar (an acid in
powder form) when you cook them. (This, of course, doesn't work when you baking them.) If
2
+
you want to know the chemistry behind stem-end blackening, read on. Ferrous oxide (Fe )
3
+
oxidizes to ferric oxide (Fe ) on heating and reacts with chlorogenic acid in the potato to form a
dark-colored spot. Why at the ends only is a mystery, that only food scientists can figure out.
Tartaric acid from cream of tartar binds with the iron and eliminates the blackening.
Occasionally you end up with black spots in other parts of the potato. These are the result
of bruising. There is no visible sign on the outside that you have an injured spud. The chemistry
of these black spots is the same oxidation as in stem-end blackening.
Surface browning of the freshly cut-up potatoes (called enzymatic browning) is easily to
solve. As you cut them up, drop them into water and the harmful oxygen in the air cannot reach
the surface.
One more reaction within the potato that concerns us is the gelatinization of the starch
granules. Potatoes are about 78 percent water, 20 percent carbohydrates and 2 percent protein.
Most of the carbohydrate is in the form of starch granules which are tiny, discrete, fairly hard,
elliptical-shaped grains that make up the body of the potato. They don't taste pleasant, which is
why no one eats potatoes raw. The starch granules gelatinize when you apply heat (137°to
1
50°F or 58°to 66°C), just like when you bake bread or cake. This temperature range is called
the gelatinization range, and is an all-important reaction in potato cooking or baking. The
compact starch granules absorb water from the surroundings and swell up to many times their
original sizes, forming a soft, moist amorphous mass.
When you stick a skewer in a still-baking potato to test for doneness and the center still
feels hard, what you feel is a mass of ungelatinized starch granules that haven't yet reached the
critical gelatinization temperature. Once the inside is around 150°F (66°C), the potatoes are done
and ready to serve. But to develop a brown skin and full, rich flavor, wait until the temperature is
close to 190°F (88°C). You may want to stick an accurate thermometer in the potato next time
instead of a skewer to check for doneness.
The fact that potatoes are so high in starch gives them great thickening power in soups
and stews. The starch granules are pretty well bound together in the raw potato, but as you cook
the pieces, some escape into the surrounding liquid and gelatinize, swelling to many times their
original size by absorbing, thus thickening, the liquid. To thicken even more, grate a little raw
potato into the soup before cooking.
Points to Remember
¨
You don't need high-priced import to make good pasta. Any pasta works that cooks into firm,
non-sticky product.
play © erdosh 198
Page
Quick Jump
|