The yeast plant and its allies are saprophytes and form no chlorophyll.
In 1857 Pasteur decisively proved that fermentation was a physiological process, for he showed that the yeast which produced fermentation was no dead mass, as assumed by Liebig, but consisted of living organisms capable of growth and multiplication.
In course of an investigation in 1822-1823 on the effects of heat and pressure on certain liquids he found that for each there was a certain temperature above which it refused to remain liquid but passedintothegaseous state, no matter what the amount of pressure to which it was subjected, and in the case of water he determined this critical temperature, with a remarkable approach to accuracy, to be 362° C. He also studied the nature of yeast and the influence of extreme cold upon its life.
These investigators regarded yeast as a plant, and Meyer gave to the germs the systematic name of "Saccharomyces" (sugar fungus).
Thenard stated that yeast was the cause of fermentation, and held it to be of an animal nature, since it contained nitrogen and yielded ammonia on distillation, nor was it conclusively proved that the yeast cell was the originator of fermentation until the researches of C. Cagniard de la Tour, T.
The preference exhibited by yeast cells for sugar molecules is shared by mould fungi and soluble enzymes in their fermentative actions.
In 1897 Buchner submitted yeast to great pressure, and isolated a nitrogenous substance, enzymic in character, which he termed "zymase."
This body is being continually formed in the yeast cell, and decomposes the sugar which has diffused into the cell.
It has not, however, been possible to transform a typical top yeast into a permanent typical bottom yeast.
Their selection for a particular purpose depends upon some special quality which they possess; thus for brewing certain essentials are demanded as regards stability, clarification, taste and smell; whereas, in distilleries, the production of alcohol and a high multiplying power in the yeast are required.
By the judicious selection of a type of yeast it is possible to improve the bouquet, and from an inferior must obtain a better wine or cider than would otherwise be produced.
This body has been prepared from active yeast, and from fruits and other parts which have been kept for some time in the absence 01 oxygen.
It may also take place where rapid proliferation of the cell is going on, as in the budding of the Yeast plant.
Cell budding takes place in yeast and in the formation of the conidia of Fungi.
Of the greatest importance is the alcoholic fermentation brought about by yeast cells (Saccharomyces cerevisiae seu vini); this follows the equation CH120 6 =2C 2 H 6 0+2CO 2, Pasteur considering 94 to 95% of the sugar to be so changed.
Pasteur found that, when cane sugar was fermented by yeast, 49.4% of carbonic acid and 51.1% of alcohol were produced; with expressed yeast juice cane sugar yields 47% of carbonic acid and 47.7% of alcohol.
Duclaux stated that the yeast question as regards low fermentation has been solved by Hansen's investigations.
The beer yeast S.
In the zymo-technical industries the various species of yeast exhibit different actions during fermentations.
In a top fermentation - typical of English breweries - the yeast rises, in a bottom fermentation, as the phrase implies, it settles in the vessel.
The small twigs, tied in bundles, are boiled for some time in water with broken biscuit or roasted grain; the resulting decoction is then poured into a cask with molasses or maple sugar and a little yeast, and left to ferment.
The great distillery at Carsebridge yields an immense supply of yeast as well as whisky.
No spores make their appearance, the yeast in question may be regarded as S.
Some observers consider that the yeast nucleus possesses a typical nuclear structure, and exhibits division by mitosis, but the evidence for this is not very satisfactory.
The principal industries include tanning, dyeing, tile-making, milling, the production of yeast and there is a large establishment for the manufacture of railway stock.
The vomiting may take place every two or three days, enormous quantities of undigested food mixed with frothy, yeast-like mucous being thrown up. And whilst the stomach is slowly filling up again after one of these uncontrollable emptyings, sudden and violent movements of the individual may cause the fluid to give rise to audible "splashings."
One chief means employed by nature in accomplishing this object is the investment of those parts of the organism liable to be attacked with an armour-like covering of epidermis, periderm, bark, &c. The grape is proof against the inroads of the yeastplant so long as the husk is intact, but on the husk being injured the yeast-plant finds its way into the interior and sets up vinous fermentation of its sugar.
A separation of a-acrose was made by acting with beer yeast, which destroyed the ordinary fructose and left /-fructose which was isolated as its osazone.
It was, for nearly two years after this, rye and Indian meal without yeast, potatoes, rice, a very little salt pork, molasses, and salt; and my drink, water.
In 1894 and 1895, Fischer, in a remarkable series of papers on the influence of molecular structure upon the action of the enzyme, showed that various species of yeast behave very differently towards solutions of sugars.
In this respect the plasma behaves in a similar manner towards the sugars as does the living yeast cell.
Hansen set himself the task of studying the properties of the varieties of yeast, and to do this he had to cultivate each variety in a pure state.
A volume of the diluted yeast was introduced into flasks containing sterilized wort, the degree of dilution being such that only a small proportion of the flasks became infected.
To effect this some of the nutrient gelatin containing yeast cells is placed on the under-surface of the cover-glass of the moist chamber.
The contents of the flasks can then be introduced into larger flasks, and finally into an apparatus suitable for making enough yeast for technical purposes.
This method obtains when yeast is vigorously fermenting a saccharine solution.
The decomposition of the complex molecule of the sugar liberates a certain amount of energy, as can be seen from the study of the fermentation set tig by yeast, which is a process of this kind, in that it is intensified by the absence of oxygen.
Liebig and Pasteur were in agreement on the point that fermentation is intimately connected with the presence of yeast in the fermenting liquid, but their explanations concerning the mechanism of fermentation were quite opposed.
Traube (1858), the active cause of fermentation is due to the action of different enzymes contained in yeast and not to the yeast cell itself.
The freshly-expressed yeast juice causes concentrated solutions of cane sugar, glucose, laevulose and maltose to ferment with the production of alcohol and carbon dioxide, but not milk-sugar and mannose.
Hansen counted the number of yeast cells suspended in a drop of liquid diluted with sterilized water.
In the yeast cell it accumulates and disappears very rapidly according to the conditions of nutrition and is sometimes so abundant as to fill the cell almost entirely (Errera, 1882, 1895: Wager and Peniston, 1910).
He emphasized the opinion that yeast derived from one cell was of no good for top fermentation, and advocated Pasteur's method of purification.
The flasks were then well shaken, and the yeast cell or cells settled to the bottom, and gave rise to a separate yeast speck.
Fischer found that the enzyme "invertase," which is present in yeast, attacks methyl-d-glucoside but not methyl-l-glucoside.
Sometimes a bottom yeast may for a time exhibit signs of a top fermentation.
In the yeast cell the nucleus is represented by a homogenous granule, probably of a nucleolar nature, surrounded and perhaps to some extent impregnated by chromatin and closely connected with a vacuole which often has chromatin at its periphery, and contains one or more volutin granules which appear to consist of nucleic acid in combination with an unknown base.
Another fact of considerable technical importance is, that the various races of yeast show considerable differences in the amount and proportion of fermentation products other than ethyl alcohol and carbonic acid which they produce.
Only those cultures which contained a single yeast speck were assumed to be pure cultivations.
He recommended that yeast should be purified by cultivating it in a solution of sugar containing tartaric acid, or, in wort containing a small quantity of phenol.