WINE, CIDER AND VINEGAR These beverages are prepared from the sugar containing juices of fruits by means of the alco holic fermentation produced by microorganisms known as yeasts. The fermented juice of grapes is known as "wine," while that produced from apples is "cider." Technically, they are very similar. Fermented pear juice is known as pear cider or "perry." The juices of certain fruits or vegetable bodies other than grapes may result in the forma tion of special kinds of so-called "wines," as "elder blow wine," "rhubarb wine," and the like. These are produced, however, only on a very small do mestic scale, and have no importance commercially.
The alcoholic fermentation.
The alcoholic fermentation, which is the basic process on which the preparation of cider and wine depends, is a chemical change induced in sugar solutions by the activity of a group of microorganisms technically known as the Sacchar oinyeetes, and commonly spoken of as "yeasts." Of these there are a large number of species, but the ones of industrial importance, so far as their utilization is concerned, fall, in general, into two more or less distinct types. One of these, the Saccharomyces cerev isite type, includes the yeasts employed technically in brewing, fermentation preceding distillation, as in the manufacture of spirits and of whisky, and in the preparation of compressed yeasts or other yeasts for bakery or domestic purposes. The second type. the Sacchar omyces ellipsoideus, is used in the fermentation of wine and cider, champagne, and in the fermenta tion for distillation of brandy. All these organ isms are widespread in nature, the Saccharomyccs ellipse ideus being found especially on the surfaces of ripe fruits and in the soil of orchards and vine yards.
The chemical change induced by these organisms consists in the breaking up of sugar into alcohol and carbon dioxid, the latter, a gaseous product, escaping for the most part, unless special effort is made to confine it or absorb it in the fermented liquid itself. Chemically, the change may be
expressed by the equation This equation, while expressing the change theo retically, is not absolutely exact, as small quanti ties of other products, generally called the by products, are also formed. These include glycerin, succinic acid and traces of other acids and ethers.
Since the fruit juices in general contain con siderable amounts of sugar, these are especially susceptible to the alcoholic fermentation, and require only that the organisms resident on the surfaces of the fruits be brought in contact with the juice in order that the change may take place. This is generally accomplished by crushing or grinding the fruits, and in this way the yeasts, together with other organisms which may also be present on the fruits, come into intimate contact with the sugary juice.
If the desired organisms are predominant, the fermentation is likely to proceed normally and give a good product. If, on the other hand, organisms of less desirable types gain the ascendency, the fermentation may result in a wine or cider which is bitter, turbid, or in other ways abnormal and unsatisfactory. This may be prevented in a great measure by introducing into the freshly expressed juice a pure culture of a desirable yeast, and thereby artificially making certain that the proper type of organism is in a suitable excess. The fer mentation may thus he controlled in a way analo gous to the control of brewing operations by the use of a pure culture of yeast.
The course of the fermentation is somewhat as follows: After the crushing of the fruit, pressure is applied and a juice, more or less colored, accord ing to the kind of fruit, is obtained. In wine making, this is known as the must; in cider-making, it is sweet cider. This juice may be nearly clear, or it may be rather turbid, and contains, besides the sugar. some acid, the natural acid of the fruit, ethers, salts and other soluble matters.