July 30, 1870.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
81 
ALCOHOLIC FERMENTATION. 
BY BARON YON LIEBIG. 
(Continued from p. 64.) 
Pasteur thinks that in the fermentation of yeast 
the cellulose of the old mother-cells is converted into 
sugar, part of which is consumed in the formation of 
the cell-membrane of the young sprouts, while an¬ 
other part must he converted into alcohol, carbonic 
acid, succinic acid, etc. This view might be readily 
tested by determining the cellulose and the alcohols. 
In the same proportion as alcohol was formed cellu¬ 
lose should disappear. 
I have endeavoured to prepare cellulose from yeast 
by Sclilossberger’s method,* but I have not succeeded 
in obtaining it quite free from nitrogen. I did not 
obtain more than 17 per cent, from the yeast, gene¬ 
rally less. Pasteur found in three experiments 
17*77, 19*29, and 19*21; mean, 18*76 per cent. 
The determination of the alcohol is not difficult. 
The yeast used for this purpose was bottom 
yeast; it was washed with water, and separated by 
means of a fine sieve from the remains of hops and 
beer. What passed through the sieve was allowed 
to settle ; the deposit, mixed with ten times its bulk 
of water and repeatedly washed with fresh water by 
decantation, until the supernatant water was no 
longer coloured. After this treatment the yeast 
presented no foreign cells when examined by the 
microscope. 
As already mentioned, the fermentation of yeast 
takes place most freely at 30° or 35° C., and after 
thirty-six hours there is no further evolution of gas. 
A temperature of 60° C. kills the yeast-cells; after 
exposure to this temperature in water, they no longer 
undergo fermentation, and do not cause fermentation 
in sugar solution. 
I. 1500 c.c. moist yeast, = 147 grin, dry yeast, 
gave, after eighteen hours, 14*792 weak alcohol, 
0*8472 sp. gr. — 11*981 alcohol. 
II. 1200 c.c., = 48*81 grm. dry yeast, gave, after 
thirty-six hours, 6*188 alcohol. 
III. 1200 c.c., = 91*5 grm. dry yeast, gave, after 
twenty-four hours, 8*23 alcohol. 
IV. 1000 c.c., = 79*22 grm. diy yeast, gave, after 
eighteen hours, 6*66 alcohol. 
V. 1000 c.c., = 100*58 grm. dry yeast, gave, after 
thirty-six hours, 13*9 alcohol. 
Reducing the alcohol obtained in these five expe¬ 
riments to cellulose, for comparison with the cellu¬ 
lose contained in the yeast taken, the following re¬ 
sults are obtained:— 
Yeast. 
Cellulose. 
Equivalent 
alcohol. 
Alcohol 
obtained. 
Percentage of 
the cellulose. 
I. 
147*0 
27*57 
15*7 
11*98 
7 6 per cent. 
II. 
48*8 
9*16 
5*2 
6*18 
118 „ 
III. 
91*5 
17*16 
9*7 
8*23 
87 „ 
IV. 
79*22 
13*85 
7*8 
6*66 
85 „ 
V. 
100*58 
18*86 
11*26 
13*90 
120 „ 
In these calculations, Pasteur’s determination of 
the amount of cellulose has been adopted. 
It will be seen that the amount of alcohol obtained 
was greater in proportion to the duration of the fer¬ 
mentation. 
If this alcohol were formed from the cellulose of 
the yeast cell-walls, all the cells should have disap¬ 
peared in the experiments II. and V.; but it was evi¬ 
dent that the cells were not reduced in quantity, and 
that they do not disappear. 
* Ann. Ch. Pk. vol. li. p. 205. 
Third Series, No. 5. 
The cellulose was determined in the deposit from 
experiment V., and it amounted to 11*75 grm., inde¬ 
pendent of loss in the operation. 
According to the microscopic examination by 
Prof. Niigeli, “ the cells of yeast that has been fer¬ 
mented without sugar exactly resemble in form and 
size the cells of ordinary yeast; they differ from 
them in so far that they clo not sprout any more, 
in having coarser and thicker cell-membrane, in 
their granular and reduced plasma contents,”—they 
are, in fact, dead cells, and the process of yeast fer¬ 
mentation consists hi the destruction of the cell 
contents. During this fermentation there is no 
perceptible smell of putrefaction. 
The liquid obtained by washing the fermented 
yeast, gives, on boiling, a coagulum similar to al¬ 
bumen : baryta water produces a precipitate of 
phosphate : mixed with alcohol as long as it is ren¬ 
dered turbid, a syrupy mass separates, and after the 
alcohol is removed, the clear, yellow, supernatant 
liquid deposits crystals which consist of ordinary 
leucin. 
The substance precipitated by alcohol is highly 
nitrogenous and contains sulphur. The residue (con¬ 
sisting of dead cells) washed and dried, is a brown, 
tough mass, containing on the average 5*64 per cent, 
nitrogen and *493 sulphur. The first yeast contained 
7*4 per cent, nitrogen or 1*76 per cent, more than 
the fermented yeast. It is evident, therefore, that in 
the fermentation of yeast, its nitrogenous constituent 
undergoes decomposition; the greater part of it be¬ 
comes soluble and part remains in the yeast cells. 
Weak potash solution dissolves out of them a sub¬ 
stance similar to casein, but containing only 11*39 
per cent, nitrogen. 
It is clear that if it is not the cellulose of the yeast 
which yields material for production of alcohol and 
carbonic acid, these must originate from a substance 
analogous to sugar and constituting part of the cell 
contents. Moreover, since this substance cannot be 
extracted by washing the yeast, it must be in the 
state of a fixed compound with some other substance 
in the cell which contains nitrogen and sulphur. 
Reducing to sugar the alcohol obtained in ex¬ 
periment V., it represents 27 grm. (C 12 H 12 0 12 ), and 
adding this to the cellulose in 100 parts of yeast the 
sum of the non-nitrogenous constituents would be 
45*6 according to Pasteur, or 43*5 per cent, according 
to my determination of cellulose. Hence there would 
remain 54*4 or 56*5 per cent, nitrogenous substance, 
containing 7*41 nitrogen, corresponding to 13 or 13*5 
per cent, nitrogen in this substance, about 1*5 or 2 
per cent, less than in the albuminates. Considering 
that yeast must contain less than 16*5 per cent, of 
pure cellulose, with some solid and liquid tat, and a 
bitter, resinous substance, probably derived from 
hops,* there would be no great error in assuming that 
in yeast the substance containing nitrogen and sul¬ 
phur is either an albuminate or one closely related: 
there can be no doubt that it originates from an 
albuminate. 
There is, I believe, no difference of opinion as to 
the behaviour of yeast in beer wort; so soon as per¬ 
fect yeast-cells have been formed, the decomposition 
of sugar commences, and at the same time the for¬ 
mation of yeast goes on incessantly until all the sugar 
is decomposed. 
As alreadj 7 * mentioned, the breaking up of sugar is 
* Scklosskerger, op. cit. p. 198. 
