Experimental cookery

The vegetables with a fairly high sugar content usually have a sweeter flavor if steamed or if just enough water is used to cook them and it is evaporated to dryness at the end of the cooking period. Even mild-flavored onions may be sweeter and better flavored if the water is evaporated than when an excess is left. But there seem to be some exceptions to most rules, and the choice of method of cooking is often a matter of judgment or circumstance. More could be written about flavor, but it has been men- tioned so often in connection with different constituents of fruits and vegetables that a great deal would be repetition. A combination of sugar, acids, and aromatic substances gives flavors that render fruits and vegetables palatable and attractive food products. EFFECTS OF ALKALIES, ACIDS, AND CALCIUM 129 Aromatic compounds. This classification is not given as a plant chemistry one, but as a group to include all substances that may give characteristic odor and thus flavor to foods. Many of the aromatic compounds are esters, like amyl acetate, which gives a characteristic odor to pears and is called *'pear oil." The odor of pineapple is due to methylbutyrate, w^hich is designated "pineapple-oil." Isoamyl isovalerate produces the characteristic odor of apples. Thatcher includes all the substances that give characteristic odor to plants under the term "essential oils and resins." Some of these substances are terpenes, alcohols derived from terpenes, the phenols, and sulfuretted oils. Oils of lemon, peppermint, cinnamon, clove, lavender, and others are classified as essential oils. AUyl isosulfocyanide, oil of mustard, and allyl sulfide, oil of garlic, con- stitute the best known of the oils containing sulfur. Tannins impart an astringent, bitter flavor to some foods. Cellulose Cellulose forms the structural, fiber, or woody part of the plant. Other substances such as pectic substances may occur in combination with cellu- lose. In the young plants or the new growth of older plants the cell walls are at first yielding. As they mature, they grow more resistant and may change physically and chemically, their function becoming more specialized with the occurring changes. In tree trunks some cell walls become woody or lignified. Doree and Barton-Wright state that the stone cells distributed throughout the flesh and particularly near the core of pears are lignified cellulose. Cellulose is a carbohydrate. It is found in plants in several forms. There is no unanimity of opinion regarding its definition, although the cotton fiber is always taken as a standard cellulose product. Hemlcellulose, wood cellulose, and gelatinized cellulose are names given to different forms of cellulose. Probably each group includes several prod- ucts. Schorger defines hemicellulose as "A polysaccharide soluble in dilute alkalies and convertible into simple sugars by heating with dilute acids at atmospheric pressure." He adds that a hemicellulose in the natural state should be insoluble in boiling water.