of water, and unless they are exposed to a 
temperature at least above the freezing-point. 
When dry or freezing, many of them conti- 
nue long without alteration. Hence we have 
an obvious method of preventing fermenta- 
tion. 
Sugar, gum, sarcocol, starch, indigo, wax, 
I resins, camphor, caoutchouc, sandaracha, 
| gum-resins, wood, and suber, though, mixed 
| with water, and placed in the most favour- 
i able temperature, shew scarcely any ten- 
| dency to change their nature. Oils absorb 
I oxygen from the atmosphere, but too slowly 
I to produce any intestine motion. Tan, some 
of the acids, and extract, are gradually de- 
I composed; the surface of the liquid becomes 
I mouldy, and an insipid sediment falls to the 
I bottom ; and when the process has once be- 
i gun, it proceeds with greater rapidity. Al- 
bumen and iibrina putrefy very quickly, but 
the products have not been ascertained; glu- 
1 ten gradually changes into a kind of cheese. 
But it is when several of the vegetable 
principles are mixed together that the fer- 
| mentation is most perceptible, and the change 
most remarkable. Thus when gluten is add- 
! ed to a solution of sugar in water, the liquid 
I soon runs into vineghr, or in certain cases to 
alcohol and vinegar. When gluten is mixed 
| with starch and water, alcohol and vinegar 
! usually make their appearance; but the 
I greatest part of the starch remains unaltered. 
| It has #een observed that certain substances 
I are peculiarly efficacious in exciting fermen- 
tation in others. These substances have re- 
1 fceived the name of ferments. 
But the phenomena of fermentation do not 
i appear in their greatest perfection in our 
artificial mixtures of vegetable principles. 
Those complicated parts of plants in which 
J various principles are already mixed by na- 
ture, especially the liquid parts, exhibit the 
| finest specimens of it; such as the sap of 
trees, the juices of fruits, the decoctions of 
| leaves, seeds, & c. It is from such natural 
mixtures that we obtain all the products of 
fermentation which mankind have applied to 
: useful purposes ; such as indigo, beer, bread, 
j vinegar, wine, &c. We shall first treat of 
the fermentation which takes place during 
the making of bread; secondly, of the 
fermentation which produces intoxicating li- 
quors; and thirdly, of the fermentation 
which produces vinegar. These are usually 
| called the panary, vinous, and acetous fer- 
mentations. 
Fermentation, panary. Simple as the 
! manufacture of bread may appear to us who 
j have been always accustomed to consider it 
j as a common process, its discovery was pro- 
j bably the work of ages, and the result of the 
I united efforts of men whose sagacity, had 
| they lived in a more fortunate period of so- 
I ciety, would have rendered them the rivals 
i of Aristotle or of Newton. 
The method of making bread similar to 
ours was known in the East at a very early 
period ; but neither the precise time of the 
discovery, nor the name of the person who 
published it to the world, has been preserv- 
ed. We are certain that the Jews were ac- 
quainted with it in the time of Moses, for in 
Exodus (ch. xii. 15.) we find a prohibition to 
use leavened bread during the celebration of 
the passover. It does not appear, however, 
to have been known to Abraham ; for we hear, 
in his history, of cakes frequently, but no- 
FERMENTATION. 
thing of leaven. Egypt, both from the na- 
ture of the soil and the early period at which 
it was civilized, bids fairest for the discovery 
of making bread. It can scarcely be doubt- 
ed that the Jews learned the art from the 
Egyptians. The Greeks assure us, that they 
were taught the art of making bread by the 
god Pan. We learn from Homer that it was 
known during the Trojan war. The Ro- 
mans were ignorant of the method of mak- 
ing bread till the year 580 after the building 
ot Rome, or 200 years before the com- 
mencement of the Christian a?ra. Since that 
period the art lias never been unknown in 
the south of Europe : but it made its way to 
the north very- slowly ; and even at present 
in many northern countries, fermented bread 
is but very seldom used. 
The only substance well adapted for mak- 
ing loaf-bread, is wheaten flour, which is 
composed of three ingredients : namely, 
gluten, starch, and a sweet mucous matter, 
which possesses nearly the properties of 
sugar, and which is probably a mixture of 
sugar and mucilage. It is to the gluten that 
wheat-flour owes its superiority to every 
other as the basis of bread. Indeed there 
are only two other substances at present 
known of which loaf-bread can be made: 
these are rye and potatoes. The rye loaf is 
by no means so well raised as the wheat 
loaf; and potatoes will not make bread at all 
without particular management. Potatoes, 
previously boiled and reduced to a very fine 
tough paste by a rolling-pin, must be mixed 
with an equal weight of potatoe-starch. This 
mixture, baked in the usual way, makes a 
very white, well-raised, pleasant bread. We 
are indebted for the process to Mr. Parmen- 
tier. Batley-meal perhaps might be substi- 
tuted for starch. 
The baking of bread consists in mixing 
wheat-flour with water, and forming it into a 
paste. The average proportion of these is, 
two parts of water to three of flour. But this 
proportion varies considerably, according to 
the age and the quality of the flour. In ge- 
neral, the older and the better the flour is, 
the greater is the quantity of water required. 
If the paste, after being thus formed, is al- 
lowed to remain for some time, its ingre- 
dients gradually act upon each other, and 
the paste acquires new properties. It gets a 
disagreeable sour taste, and a quantity of gas 
(probably carboffic acid gas) is evolved. In 
short, the paste ferments. These changes 
do not take place without water : that liquid, 
therefore, is a necessary agent. The gluten 
is altered, and probably acts on the starch ; 
for if we examine the paste after it has un- 
dergone fermentation, the gluten is no long- 
er to be found. If paste, after standing for 
a sufficient time to ferment, is baked in the 
usual way, it forms a loaf full of eyes like our 
bread, but of a taste so sour and unpleasant, 
that it cannot be eaten. If a small quantity 
of this old paste, or leaven as it is called, is 
mixed with new-made paste, the whole be- 
gins to ferment in a short time; a quantity 
of gas is evolved ; but the glutinous part of 
the flour renders the paste so tough, that 
the gas cannot escape ; it therefore causes 
the paste to swell in every direction : and if 
it is now baked into loaves, the immense 
number of air-bubbles imprisoned in ever}’ 
part renders the bread quite full of eyes, and 
very light. If the precise quantity of leaven 
717 
necessary to produce the fermentation, and 
no more, has been used, the bread is suffi- 
ciently light, and has no unpleasant taste; 
but if too much leaven is employed, the bread 
has necessarily a bad taste; if too little, the 
fermentation does not come on, and the bread 
is too compact and heavy. To make good 
bread with leaven, therefore, is difficult. 
The undent Gauls had another method of 
fermenting bread. They formed their paste in 
the usual way ; and, instead of leaven, mixed 
with it a little of the barm or yeast which col- 
lects on the surface of fermenting beer. Tins 
.mixture produced as complete and as speedy 
a fermentation as leaven ; and it had the 
great advantage of not being apt to spoil tin- 
taste of the bread. About the end of the 
17th century, the bakers in Paris began to 
introduce this practice into their processes 
The practice was discovered, and exclaimed 
against; the faculty of medicine, in 1688, 
declared it prejudicial to health; and it was 
not till after a long time that the bakers suc- 
ceeded in convincing the public that break 
baked with barm is superior to bread baked 
with leaven. In this country the bread lias 
for these many years been fermented with 
barm. 
With respect to the Mature of the barnr 
which produces' these effects, Mr. Henry of 
Manchester has proved, by a number of 
very interesting experiments, that carbonic 
acid is capable of being employed in many 
cases with success as a substitute for barm. 
But the analysis of Mr. Westrum has de- 
monstrated, that the barm which collects on 
the surface of beer is of a much more com- 
plicated nature. That celebrated chemist 
obtained from 15060 parts of good barm tile 
following substances: 
15 carbonic acid 
10 acetic acid 
45 malic acid 
240 alcohol 
120 extractive 
240 mucilage 
315 sugar 
480 gluten 
13595 water 
15060. 
Resides 69 parts of lime, 1.3 potass, some sac- 
lactic acid, and traces of phosphoric acid 
and silica. 
But all these ingredients are not essential 
to barm. Westrum ascertained that the ex- 
tractive, mucilage, sugar, and malic acid, 
are incapable of producing fermentation ; that 
barm, deprived of its gluten by filtration,, 
loses the property of exciting fermentation 
in beer; that the gluten of wheat is capable 
aloneof exciting a fermentation ; and that glu- 
ten, mixed with a vegetable acid, answers all 
the purposes of a ferment. Hence it follows, 
that these bodies alone are essential to barm. 
But leaven is precisely such a compound. 
After the bread has fermented, and is pro- 
perly raised, it is put into fhe oven, which is 
previously heated, and allowed to remain till- 
it is baked. The mean heat of an oven, as 
ascertained by Mr. Tillet, is 448. The bakers 
do not use a thermometer ; but they judge 
that the oven has arrived at the proper heat 
when flour thrown on the floor of it becomes 
black very soon without taking fire. We see, 
from Tillet/s experiment, that this happens at 
44S°, 
