Experimental cookery

Salsify probably contains large amounts of tannic substances. It turns dark when peeled even if put under water unless a little vinegar is added to the water to acidify it. Salsify or oyster plant and sometimes other vegetables such as carrots stain the fingers when they are pared. This may be due in part to tannins. Lemon juice is effective in removing or lightening such stains because of its acidity. Other discolorations with tannins. Brownish or black discolorations of vegetables in vinegar have been caused by the tannin of the vinegar combining with the iron of the food. The use of a tannin-free vinegar does away with this difficulty. Greenish black spots in chocolate ice cream were traced to the tannin supplied by the chocolate or cocoa and the iron from rusty spots in the can. In green-colored beer the iron came from exposed pipes, the tannin from the hops. According to Atwater, cherry juice, now commercially marketed, when mixed with gelatin for a molded dessert, sometimes gave a gummy, purplish precipitate. The precipitate was caused from combination of the tannin of the juice with the protein, gelatin; the purplish color came from combina- tion with metals. Discoloration of pared fruit, considered at greater length in the next section, is caused by tannin compounds in combination with enzyme action. Tea. Black tea is darker than green tea because of oxidation of tannins in the leaf during drying and fermentation. It is also less astringent than green tea because the tannins are in a less soluble form. Tannins also give precipitates of calcium, magnesium, and iron tannates, when these minerals are present .in the water. The film on coffee or tea is from these tannates. When lemon or orange is added to tea, the film usu- ally disappears, for in acid the tannins often lose the darker color acquired in an alkaline medium. Tannins lower the surface tension of water, and the water in which vegetables containing tannins are cooked is apt to froth or foam. Enzymes Enzymes control many of the complex chemical processes of plant metab- olism. They accelerate reactions which would otherwise take place very slowly, and though they may initiate the reaction, do not form part of its final product. Reactions of several enzymes have been mentioned. A large number of the enzymes are hydrolytic, including the proteinases, lipases, amylases, and others; but there are also oxidizing and reducing and other groups of enzymes. Some of the plant enzymes that digest proteins are 124 FRUITS AND VEGETABLES of slight interest in cookery. An enzyme of the pitcher-plant hydrolyzes fibrin. Bromelin of pineapple acts on native proteins, its effect being more often noticed in cookery when uncooked pineapple is added to gelatin, which is liquefied. Papain of the papaw leaf acts on native proteins. Some experiments were tried at the Office of Home Economics to utilize the papaw leaf, the dried powdered leaf, or the extracted enzyme to render tough meat tender. These did not indicate that papain could be successfully used in this way, as the enzyme acted on the surface, powdering or pul- verizing it in only a thin layer even after being in contact with the meat for several hours, the interior of the meat not being affected.