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.
The beer yeast S.
Cell budding takes place in yeast and in the formation of the conidia of Fungi.
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.
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.
These investigators regarded yeast as a plant, and Meyer gave to the germs the systematic name of "Saccharomyces" (sugar fungus).
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.
About this time Hansen, who had long been engaged in researches on the biology of the fungi of fermentation, demonstrated that yeast free from bacteria could nevertheless occasion diseases in beer.
Duclaux stated that the yeast question as regards low fermentation has been solved by Hansen's investigations.
It has not, however, been possible to transform a typical top yeast into a permanent typical bottom yeast.
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.
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.
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.
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."
The beginning of definite knowledge on the phenomenon of fermentation may be dated from the time of Antony Leeuwenhoek, who in 1680 designed a microscope sufficiently powerful to render yeast cells and bacteria visible; and a description of these organisms, accompanied by diagrams, was sent to the Royal Society of London.
In this respect the plasma behaves in a similar manner towards the sugars as does the living yeast cell.
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.
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.
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 formation of spores is used as an analytical method for determining whether a yeast is contaminated with another species, - for example: a sample of yeast is placed on a gypsum or porcelain block saturated with water; if in ten days at a temperature of 52° F.
No spores make their appearance, the yeast in question may be regarded as 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.
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.
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.
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.
The great distillery at Carsebridge yields an immense supply of yeast as well as whisky.
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.
Lxxii.; Wager and Peniston, Cytological Observations on the Yeast Plant, Ann.
The only groups of plants in which typical nuclei have not been found are the Cyanophyceae, Bacteria and Yeast Fungi.
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.
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.