_Of Yeast, its nature, and contents, and of the manner and
quantities in which it is to be added to the worts._
Musts, or worts, though ever so rich, when unfermented, yield no
spirit by distillation, nor inebriate, if drank in any quantity. The
oils, as yet not sufficiently attenuated for this purpose, become so
only by fermentation. Air is absolutely necessary for this process,
in the course of which, some of the aerial parts mixing with, and
being enveloped by, oils greatly thinned, are enclosed in vesicles not
sufficiently strong to resist the force of elasticity, or prevent a
bursting and explosion. In the progress of the act, the air joins with
oils both coarser, and charged with earthy particles, a coat is formed
capable of resisting its expansion, and if the bubbles cannot come to
a volume sufficient to be floated in and upon the liquor, they sink to
the bottom, and take the appellation of _lees of wine_.
Between these two extremes, there is another case, when the bubbles are
sufficiently strong to hold the air, but not weighty enough to sink.
After floating in, they emerge, and are buoyed upon the surface of the
liquor, and there remaining entire, are termed the _flowers of wine_.
Both lees and flowers are, therefore, vesicles formed out of the
must, filled with elastic air, and, either separately, or when mixed
together, they obtain the general denomination of _yeast_.
We have often mentioned the power of fire, in driving the air out of
worts. Yeast, fraught with the principle now wanted for fermentation,
is, therefore, the properest subject to be added to the must; but
its texture is various, in proportion to the different heats of the
extracts it was formed from. Keeping drinks, extracted with hotter
waters, yield yeast, the oils of which have a greater spissitude. It
is consequently slower, more certain, and most fit to promote a cool
and gentle fermentation. That, on the contrary, which is produced from
small beer, being weak, and acting at once, is apt to excite a motion
like that of effervescence; such yeast ought, therefore, not to be
used, but when there is no possibility to obtain the other.
The longer wines or beers are under the first act of fermentation, the
greater variety will be found in the texture of the bubbles, which
compose their flower and lees. Wines made out of grapes, in general,
require a time somewhat longer than the worts of malt, before this
first period is at an end; and we have seen, that in them fermentation
first brings forth air bubbles, whose constituent parts are most
tender, and afterwards some that are of a stronger texture. As malt
liquors require a less time to ferment, their bubbles are more similar:
on this account, the whole quantity of yeast necessary to a wort
should not be applied at once, lest the air bladders, bursting nearly
in the same time, should prevent that gradual action, which seems to be
the aim of nature in all her operations.
Keeping beers, formed from low dried malts, occasion the greatest
variety of heat in the extracts, and from hence these musts form
yeast, whose bubbles differ most in magnitude and strength. A drink,
then, properly made from pale malt, nearly resembles natural wines,
especially when they are so brewed as to require precipitation to
become transparent.
_Cleansing_ is dividing the drink into several casks; this checks the
motion occasioned by fermentation, and consequently retards it. To
prevent this from being too sensibly felt, some yeast should be put
to the drink, before it is removed into the casks. As the constituent
parts, in strong beers, are more tenacious than in small, and require
a greater motion to entertain the fermentation, the drinks, before
they be thus divided, should, besides the addition of the yeast, be
well roused with a scoop, or by some other means, for one hour. This
not only blends all the parts together, but attenuates and heats the
liquor, and makes it more ready to begin to ferment again, when in the
casks. One sixth part of the whole of the yeast used is generally
reserved for this purpose; and the remainder is equally divided as the
worts are let down. It must be observed, that this stirring, though as
necessary to small, as to strong drinks, is only to be continued for a
space of time proportioned to their strength.
We have before seen, when a grist of malt is entirely extracted to
form common small beer, soon to be expended, one gallon of yeast to
eight bushels of grain affords a sufficient supply of air to perfect
the fermentation. This takes place when the heat of the air is at 40
degrees, but, at the highest fermentable degree, experience shews,
that half that quantity is as much as is necessary. For some ales,
the whole virtue of the malt is not extracted, and what remains is
appropriated to the making of small beer: the quantity of yeast used
for these drinks must be only in proportion to the strength extracted.
From these premises, the following tables have been formed, exhibiting
the quantity of yeast proper for the several sorts of drinks, at the
different heats of the air.
A TABLE _shewing the quantities of yeast
necessary for common small beer in every
season_.
Heat of Pints of yeast to one
the air. quarter of malt.
35 9 }
40 8 } The whole quantity of yeast to be
45 8 } put into the first wort.
50 7 } ---------------------------------------
55 7 } The first wort to have 3/4
60 6 } The second wort to have 1/4
65 6 } ---------------------------------------
70 5 } The first wort to have one half of the
75 5 } whole quantity.
80 4 } The second wort to have the remainder.
A TABLE _shewing the quantities of yeast necessary for
all keeping drinks, both brown and pale, small and
strong_.
Heat of Pints of yeast to
the worts[37]. one quarter of malt.
30 6
35 6
40 6
45 6
50 6
55 5
60 5[38]
65 4
70 4
75 3
80 3
A TABLE _shewing the quantities of yeast necessary for
amber and all sorts of ales, after which small beer is
made_.
Heat Pints of yeast
of the air. to one quarter of malt.
30 7-1/2
35 7
40 7
45 6-1/2
50 6
55 5-1/2
60 5
65 4-1/2
70 4
75 3-1/2
80 3
This table is founded on the supposition that, the virtue or strength
extracted from one quarter of malt for amber, is equal to 5/6 of the
whole. In every heat of the air, the quantity of yeast to be used
for common small beer made after ale, must be one fifth part of the
quantity which the ale required, the additional strength obtained from
reboiling the hops, requiring further proportion; if, for keeping small
beer, nearly in the proportion of six pints of yeast to five barrels of
beer, this will be found to correspond with the rule delivered in the
foregoing table.