MICRO-ORGANISMS. 139 | 
it to any degree. He is scientific in his methods, and can 
repeat the process day after day with the utmost regularity, 
and with the sense of security engendered by the knowledge 
that his beer a year hence will be the same as it is today. 
Yeast and Wane. 
The vigneron is by no means so happily placed. He does 
not, crush his grapes every day, and he cannot boil his must. 
Many a vigneron does not know the benefit that can be 
derived from usimg pure cultures of yeast. A spontaneous 
fermentation is allowed to set in, with the result that yeasts 
and moulds of every creed and denomination strive for a 
mastery ; so that a wine is produced whose future career is 
wrapped in doubt. There is only one partial safeguard the 
vigneron has, and that is the acidity of the must, which 
favours the wine-yeasts, and checks other yeasts and bac- 
teria. A check, however, is not a prevention, and some 
Australian wines are prone to develop turbidity, and to 
undergo the mannitic fermentation, both of which diseases 
are caused by bacteria. But the acidity and the sugar are 
varying quantities, and it is easy to believe that the wine 
maker must be an expert, since he has to contend with so 
many difficulties. These may be to some extent overcome 
by the use of pure cultures of selected yeasts. In the selec- 
tion of a yeast, one microscopic cell is taken, and cultivated, 
and the action of the culture upon must has to be tested 
chemically, and with the trained palate. The temperature 
and the acidity best suited to its growth must also be ascer- 
tained. Perhaps the temperature is the most difficult con - 
dition the vigneron has to regulate; but it is quite possible 
that a native race of the wine-yeast, Saccharomyces ellip- 
soideus, might be found that would ferment out at an 
Australian summen temperature the sweet Australian musts. 
Although a previous pasteurisation of the must is theoreti- 
cally advantageous prior to the addition of a pure culture, 
yet, by using a large quantity of starter-yeast, the action. 
of the natural yeasts and moulds can be kept under. This 
is the principle of mass effect when 25 to 100 yeast-cells are 
added for every yeast or mould that may be on the surface 
of the grapes. The added yeasts of the starter are more 
numerous and more vigorous, and, generally speaking, finish 
the fermentation before the others have had time to begin. 
The advantages of using pure cultures in the wine-fermenta- 
tion may be summarised thus:—A quicker fermentation, a 
better clearing, a cleaner taste, and an improvement in 
flavour and bouquet. At present European yeasts are 
