IV

YEAST

[1871]

It has been known, from time immemorial, that the sweet liquids which may be obtained by expressing the juices of the fruits and stems of various plants, or by steeping malted barley in hot water, or by mixing honey with water—­are liable to undergo a series of very singular changes, if freely exposed to the air and left to themselves, in warm weather.  However clear and pellucid the liquid may have been when first prepared, however carefully it may have been freed, by straining and filtration, from even the finest visible impurities, it will not remain clear.  After a time it will become cloudy and turbid; little bubbles will be seen rising to the surface, and their abundance will increase until the liquid hisses as if it were simmering on the fire.  By degrees, some of the solid particles which produce the turbidity of the liquid collect at its surface into a scum, which is blown up by the emerging air-bubbles into a thick, foamy froth.  Another moiety sinks to the bottom, and accumulates as a muddy sediment, or “lees.”

When this action has continued, with more or less violence, for a certain time, it gradually moderates.  The evolution of bubbles slackens, and finally comes to an end; scum and lees alike settle at the bottom, and the fluid is once more clear and transparent.  But it has acquired properties of which no trace existed in the original liquid.  Instead of being a mere sweet fluid, mainly composed of sugar and water, the sugar has more or less completely disappeared; and it has acquired that peculiar smell and taste which we call “spirituous.”  Instead of being devoid of any obvious effect upon the animal economy, it has become possessed of a very wonderful influence on the nervous system; so that in small doses it exhilarates, while in larger it stupefies, and may even destroy life.

Moreover, if the original fluid is put into a still, and heated moderately, the first and last product of its distillation is simple water; while, when the altered fluid is subjected to the same process, the matter which is first condensed in the receiver is found to be a clear, volatile substance, which is lighter than water, has a pungent taste and smell, possesses the intoxicating powers of the fluid in an eminent degree, and takes fire the moment it is brought in contact with a flame.  The Alchemists called this volatile liquid, which they obtained from wine, “spirits of wine,” just as they called hydrochloric acid “spirits of salt,” and as we, to this day, call refined turpentine “spirits of turpentine.”  As the “spiritus,” or breath, of a man was thought to be the most refined and subtle part of him, the intelligent essence of man was also conceived as a sort of breath, or spirit; and, by analogy, the most refined essence of anything was called its “spirit.”  And thus it has come about that we use the same word for the soul of man and for a glass of gin.