94. Conditions Of Growth

The conditions essential to their development are the proper degree of moisture and temperature and the necessary food materials. Thoroughly dry animal and vegetable substances do not ferment. Flour and meal that have been dried to a water content of 10 per cent will keep a long time without loss from fermentative changes. The heat in a bin of new grain, with its subsequent musty condition, is due to the fermentations that are made possible through the presence of considerable moisture. Thorough drying is a preventive of destructive fermentations.

There is a temperature at which each vegetable ferment thrives best, and there are limits of temperature outside of which the growth of these forms of life does not occur, or is very slight. Numerous species thrive between 75Q and 100° F. Fermentable materials like fruit and meat at the freezing point or below are not subject to fermentations. The boiling point of water kills most bacteria, and temperatures above 150° F. retard or entirely prevent their growth.

95. Results Of Fermentations

Like all life, these organisms must have food. Many species find this in acceptable forms in vegetable and animal products. Because these products generally contain the sugar, proteins, and mineral compounds which nourish bacteria, many of them are the prey of ferments under proper conditions of moisture and heat. The prevention of fermentation in foods is desirable because it occasions a loss of nutritive value and often produces undesirable flavors. The loss becomes evident when we consider the nature of the chemical changes that occur. For instance, when sugar of cider is broken up through the influence of a bacterium, the carbon dioxid and alcohol are formed through the appropriation of free oxygen. This means that combustion occurs, causing the liberation of energy which otherwise would have been available if the sugar had been taken as food. Many fermentations involve oxidation, all of which are destructive of food value.

96. Manner Of Action

Several theories have been advanced to account for the action of the organized ferments. One is that these little plants use sugar and other compounds as food, deriving energy and growth therefrom, the carbonic acid, alcohol, and other new bodies being the by-products of this use. Another is that these organisms produce an unorganized ferment which brings about the fermentative changes, and their action is therefore indirect. Indeed, it seems to be definitely proved that it is possible to separate from the cells of the yeast plant a ferment that, in the absence of the yeast plant itself, converts sugar into carbon dioxid and alcohol. This shows that the effective agent in bacterial fermentations is, after all, a chemical substance, or an unorganized ferment. These later discoveries tend to remove the distinction that has been made between organized and unorganized ferments. Whatever may be the real explanation of the changes that occur, fermentations due to plant growth are among the most useful agencies with which we deal, and may be the most harmful. The yeast plant is an organized ferment, and in bread-making it is useful, but the putrefaction of meats under the influence of another ferment causes loss.

The digestive tract of man is inhabited by countless numbers of bacteria. These are found to some extent in the stomach, but most abundantly in the intestines, especially in the colon. The two main types in which we are interested in their relation to digestion are the fermentative or those that attack the carbohydrates, especially the sugars, and the putrefactive, or those that cause decomposition of the proteins. The former are most active in the stomach and when carbohydrate-bearing foods, especially sweets, are eaten in excess, or for any reason the food remains an abnormally long time in the stomach, as when the organ is weak muscularly, an uncomfortable, and sometimes dangerous, evolution of acids and gases occurs. As the presence of hydrochloric acid tends to inhibit the growth of these organisms, an insufficient secretion of gastric juice gives an opportunity for stomach fermentations that would not occur under normal conditions.

The putrefactive fermentations, which are favored by a heavy meat diet, begin in the lower part of the small intestine and reach their maximum in the colon. In excessive meat eating, particularly when the food residues remain for an unusually long time in the intestines, putrefactive products may be evolved to a harmful extent, sometimes causing serious results. But with healthy individuals under proper conditions of diet the bacteria present in the digestive tract are at least not harmful, and according to older views, now more or less discredited, are useful adjuncts of digestion.