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Although showing fermentation resulted from the action of living microorganisms was a breakthrough, it did not explain the basic nature of fermentation; nor did it prove it is caused by microorganisms which appear to be always present. Many scientists, including Pasteur, had unsuccessfully attempted to extract the fermentation enzyme from yeast ...
The French chemist Louis Pasteur founded zymology, when in 1856 he connected yeast to fermentation. [9] When studying the fermentation of sugar to alcohol by yeast, Pasteur concluded that the fermentation was catalyzed by a vital force, called "ferments", within the yeast cells. The "ferments" were thought to function only within living organisms.
The finest surface filtration, microfiltration, can sterilize the wine by trapping all yeast and, optionally, bacteria, and so is often done immediately prior to bottling. An absolute rated filter of 0.45 μm is generally considered to result in a microbially stable wine and is accomplished by the use of membrane cartridges, most commonly ...
The minimum weight of water required may be calculated: yeast weight x 4 = water weight. [ 4 ] Yeast viability can be tested by mixing yeast in warm water and sugar, and following a short rest period during which the cells first accommodate to the environment and then begin to grow, a layer of foam is developed by the action of the yeast, a ...
Subsequently, the yeast can be collected (cropped) from the top (ale fermentation) or the bottom (lager fermentation) of the fermenter in order to be reused for the next fermentation. Yeast flocculation is partially determined by the calcium concentration, often in the 50-100ppm range. [ 14 ]
Prior to Pasteur's research on fermentation, there existed some preliminary competing notions of it. One scientist who had a substantial degree of influence on the theory of fermentation was Justus von Liebig. Liebig believed that fermentation was largely a process of decomposition as a consequence of the exposure of yeast to air and water. [4]
The microbes or eukaryotic cells used for fermentation grow in (or on) specially designed growth medium which supplies the nutrients required by the organisms or cells. A variety of media exist, but invariably contain a carbon source, a nitrogen source, water, salts, and micronutrients. In the production of wine, the medium is grape must.
The first is the "interruption" method, whereby the primary alcoholic fermentation is interrupted by the act of bottling. The wine goes into bottle, sealed under a crown cap, where the still viable yeast, nutrient and sugar allow the primary fermentation to continue and produce the carbon dioxide that forms the bubbles.