Allen Paul W. Industrial Fermentations
Подождите немного. Документ загружается.
BREAD YEAST MANUFACTURE
315
TABLE XIV.—Continued.
Asparaginic acid
Glutaminio acid
Tyrosin
Tryptophan
Cyatin and other sulphur compounds..
OsyproHn • ,
Cholin
Glucosamin
ANALYSIS OP THB ASH.
Phosphorus pentoxid P1O1
Potassium oxid KsO
Magnesium oxid MgO
Calcium oxid CaO
Silica SiO.
Sodium oxid Na»O
Sulphur trioxid Soa
Chlorin CI
Iron Ed
3.5%
6 %
2 %
J5%
2 %
4.5%
£%
100 XX)
Courttuy
of
Flehehmann
Company.
Fia. 50.—Side view of yeast fermentors.
Preparation of Nutrient Solution.
In the preparation of nutrient wort in yeast manufacture the
following raw materials are brought together in the mash tub:
barley malt, com, malt sprouts, occasionally rye, and water. The
barley malt Efhould be high in diastatic power and also rich in pro-
316
INDUSTRIAL FERMENTATIONS
teolytic enzymes. It should be finely ground before going to the
mash tub. The corn is prepared for the mash tub by first grinding
and then cooking under steam pressure. Finally malt sprouts and
the water are added to the tub.
The water used in the mashing operation is of high purity and
is free from bacteria. Salts of calcium and magnesium in the water
make the addition of sulphuric acid necessary as these salts may reduce
the acidity of the mash. By adding sulphuric acid, magnesium and
calcium sulphates are formed which are valuable as stimulants of yeast
growth.
The object of the mashing operation is to bring the proteins of
Oovrtetg
of
FUtsdman*
Company.
Fxa. 51.—Top view of yeast fermentors.
the grains into solution and to hydrolyze the starches into sugars.
The mash at first is held at 50 to 55° C. for an hour BO that the
proteolytic enzymes of the malt can change the proteins to peptones.
After this period which favors proteolytic action the temperature of
the mash is raised to 65° C. and held for several hours at this tem-
perature so that all liquefied starch may be hydrolyzed into ferment-
able sugars by the diastase.
Next the mash is cooled to about 55° and acidified by inoculation
with pure cultures of lactic acid bacteria. The purpose of this
acidification is to protect the mash from the action of putrefactive
bacteria and at the same time to create a condition in the mash
which hastens peptonization of the proteins. When the acidification
of the mash has reached about 1.5% acid it is sterilized, filtered,
cooled and passed into the yeast fermentation tank.
BREAD YEAST MANUFACTURE
Addition of Culture.
317
To the filtered wort in the fermentator is added, from a generator,
a pure culture of yeast. The amount of this stock yeast added is
usually about 2.3% of the grain used. The concentration of the
wort may be 10%. to 11% Balling. The temperature in the fermentor
at the start of fermentation is about 22° C. and during fermentation
rises to 30° C. at which temperature it ia held. Higher temperatures
have been used but the yield of yeast is reduced. Aeration by means
Oovrtety
of
Fleiaobmann
Company.
PIG.
52.—Plate presses for expelling moisture from yeaBt.
of an air compressor is maintained for 10 to 12 hours when the yeast
growth is completed.
Separation of Yeast.
At the end of the fermentation the yeast is separated from, the
wort by use of centrifugal machines. In producing compressed yeast
of about 75% moisture from separator yeast, square iron filter presses
are used. . Finally .the yeast is passed through cake cutting and wrap-
ping machines. The ope pound package is largely used by commercial
bakeries while the small cakes are sold for use in the home.
The most important uses of yeast in bread-making are as:
A leavening agent.
An agent to help mature the gluten.
An additional nutritive substance.
A source of vitamines.
A source of the enzymes, maltase, invertase, endotrypta.se, etc.
318
INDUSTRIAL FERMENTATIONS
Coartwy of
Flehehmmn
Company.
63._Filter tanks.
Oovrtesv
of
Fleimfimann
Company.
FIG.
54J—Yeast
laboratory.
Yeast considered separately from the bread industry has oome to
be widely used as a therapeutic agent because of its vitamines,
enzymes and nucleic acid.
BREAD YEAST MANUFACTURE 319
One value ascribed to yeast nucleic acid is said to be its ability
when injected subcutaneously to increase the white corpuscle content
of the human blood.
REFERENCES ON YEAST.
Ando, K. Orig. Com. 8th Intern. Congr. Appl. Chem., 14, pp. 4-12.
Baker, J. L, 1917. .Jour. Soc. Chem. Ind., 36, pp. 836-840.
Bokomy, T. Chem. Ztg 40, pp. 366-368.
Bokorny, T. Jour. Inst. Brewing, 24, pp. 38-39.
Cook, F. C. U. 8. D. A., Bur. Chem., Circ. 62.
Demby, K. G., 1917. Bochem. Z., 81, pp. 109-208.
Dreyer.G. Z. ges. Baun. 36, pp. 201-208.
Euler, H. Jour. Chem. Boo., 112, I, pp. 71-72.
Euler, K, and Sahlen, J. Z. Garungsphymol, 3, pp. 225-234.
Gayon, U.
(
and Dubourg, E. Rev. Vit., 38, pp. 5-8.
Hayduok, F., and Bulla, D. Wochschr. Brau, 29, pp. 489-494.
Kirby, W. Chem. Ztg., 35, pp. 421-423,
Kohmann, H. A., et al., 1916. Jour. Ind. and Eng. Chem., 8, pp. 781-786.
Kofflowiw, A. Z. Garungaphyaiol, 1, pp. 230-252.
KrauB.
A. Chem. Ztg., 39, pp. 793-794.
Nowak, C A. Jour. Ind. and Eng. Chem., 5, p. 668.
Ostwald, W., 1916. Chem. Ztg., 39, p. 121.
Rufuerow, R., 1910. Pure Products, 6, No. 11, pp. 649-652.
Schonfeld, F. Wochschr. Braw, 26, pp. 521-524.
Schonfeld, F., 1916. Jour. Soc. Chem. Ind., 35, p. 1230.
Scott, W., 1915. Jour. Inst. Brewing, 21, pp. 391-446.
Thomas, P. Compt. Rend., 156, pp. 2024-2027.
Vanderelde, A. J. Orig. Com. 8th Intern. Congr. Appl. Chem., 14, pp. 191-202.
Chapter 24.
Tomato Products.
Bacteriological Control of Tomato Products.
The Bureau of Chemistry of the U. S. Department of Agriculture
considers tomato products unfit for food:
(1) When mold filaments are found in more than 66% of the
fields examined according to the Howard method.
(2) When yeasts and spores are present in excess of 125 per
1/60 cmm. according to the Howard method.
(3) When bacteria are present in excess of 100,000,000 per cc.
according to the Howard method.
It has been found that tomato products made from fermented and
mouldy tomatoes cannot pass the above requirements. In other words
microscopic control methods are practical in eliminating the use of
unfit tomatoes in the manufacture of products. Laxity in picking and
sorting of tomatoes is detected later in the finished product by
microscopic methods.
An excessive number of bacteria, yeasts, mold filaments, and
spores is evidence of the use of partly decayed tomatoes, improper
storage or dirty utensils. According to B. J. Howard there ia a
definite relation existing between the mold count and the percentage
of rot by weight used in making the product. He says that bacteria
per cc. up to 15,000,000 does not indicate per cent of rot but that for
every 20,000,000 bacteria per cc. above the first 15,000,000 indicatea
one per cent of rot used.
Cruess says that canned tomatoes and chili sauce usually run
low in microorganisms' because they are made from peeled stock.
However when considerable numbers of yeasts, molds, and bacteria
are found in these products it indicates the use of decomposed material
or careless methods.
Howard and Stephenson (1917) in Bulletin 581 of U. S. Dept. of
Agriculture give the following summary of their microscopical studies
on tomato products.
"Tomato products promptly made from stock judged acceptable
by visual inspection never show high counts of microorganisms.
Similarly, products made from stock obviously not good or from stock
improperly handled usually show high counts. It may therefore be
320
TOMATO PRODUCTS 321
assumed that high counts of organisms in such products indicate
unmistakably that the stock used was in bad condition or was
handled in an insanitary manner during manufacture.
"It was found that tomato pulp stored in barrels usually gave
high microscopical counts; henoe it would seem inadvisable to use
barrels for storing the product.
"Field work performed during the past three seasons has proved
that with proper equipment and factory management there is no
reason for stock ready for the cyclone to contain over 1 per cent of
decayed material.
"In factories where the stock is properly handled the mold count
is of greater importance than the counts on the other organisms in
judging the condition, of the raw stock. High counts of yeasts and
spores, and bacteria are more frequently an indication of secondary
than of primary spoilage. A low mold, yeast and spore, or bacterial
oount does not necessarily indicate sound stock, but a high Gount
in any of these organisms always indicates bad stock or improper
handling,
"It was found that of the samples made in the laboratory none
with less than 5.5 per cent of rot gave a mold count of more than 50.
In the oase of the factory samples the mold count rises sharply from
0 to % per oent of rot. Beyond J4 per cent the rate of rise gradually
deoreases, until after 20 per cent of rot the rate of increase is slow. A
mold count.of 40 may be obtained in samples having any amount of
rot between 2.2 and 100 per cent.
"A yeast and spore count of 20 represents about one per cent of
decay. From this point the rate of increase is slow.
"A bacterial count below 16,000,000 indicates little as to the amount
of decay. Beyond this point, however, up to 20 per cent of rot the
rate of increase is about 20,000,000 for each per cent of rot.
"An investigation of the manufacture of tomato sauces and pastes
in Italy showed that.Italian products should be equal to American
products made under similar conditions. The mold count for the
concentrated products was found to be about the same as that for
pulp,
and the yeast and spore and bacterial counte to be proportional
to the degree of concentration. Sauces and pastes made from objec-
tionable material run particularly high in yeasts, spores, and bacteria.
High oounts on this class of products, then, indicate bad stock or
insanitary handling."
The following explanation and description of microanalytica]
methods is taken from "Microscopical Studies on Tomato Products,"
by Howard and Stephenson, United States Department of Agrioulture
Bulletin No. 581.
Method for Microanalysis of Tomato Products.
"Sinoe the publication of Bureau of Chemistry Circular 68, no
statement of the microscopical method used by the department has
PLATE 12
After Eoward
in
UJBDA.
Tear Book
1011.
Molds, mold spores, and bacteria found in decaying tomatoes.
322
TOMATO PRODUCTS 323
been issued. The bureau has received repeated requests for a restate-
ment of the method including more definite details of manipulation
than were given in the circular. In 1915, after the method incorporating
the most important of these details had been rewritten, the Association
of Official Agricultural Chemists adopted it as a tentative method and
published it November 1916, in the Journal of the Association of
Official Agricultural Chemists. At the meeting of the same association
in November, 1916, a few minor changes were authorized. As it is
uncertain when the association will publish the method in its amended
form, permission has been granted by the chairman of the Board of
Editors of the Association of Official Agricultural Chemists to in-
corporate it here.
Apparatus.
"(a) Compound microscope.—Equipped with apochromatic objec-
tives and compensating oculars, giving magnifications of approximately
90,180 and 500 diameters. These magnifications can be obtained by
the use of 16 and 8 Trim Zeiss apochromatic objectives with X6 and
X18 Zeiss compensating oculars, or their equivalents, such as the
Spencer 16 and 8 mm. apochromatic objectives with Spencer X10 and
X20 compensating oculars, the drawtube of the microscope being
adjusted as directed below.
"(b) Thoma-Zeiss Blood counting cell.
" (c) Howard mold counting cell.—Constructed like a blood-count-
ing cell but with the inner disk (which need not be ruled) about 19 mm.
in diameter.
Molds (Tentative).
"Clean the special Howard cell do that Newton's rings are pro-
duced between the slide and the cover glass. Remove the cover and
place, by means of a knife blade or scalpel, a small drop of the sample
upon the central disk; spread the drop evenly over the disk and cover
with ,the cover glass so as to give an even spread to the material.
It is of the utmost importance that the drop be mixed thoroughly and
spread evenly; otherwise the insoluble matter and consequently the
molds are most abundant at the center of the drop. Squeezing out
of the more liquid portions around the margin must be avoided. In a
satisfactory mount Newton's rings should be apparent when finally
mounted and none of the liquid should be drawn across the moat and
under the cover glass.
"Place the slide under the microscope and examine with a mag-
nification of about 90 diameters and with such adjustment that each
field of view represents approximately 1.5 sq. mm. of area on the
mount. This area is of vital importance and may be obtained by
adjusting the drawtube to the proper length as determined by actual
measurement of the field, a 16 rnm. Zeiss apochromatic objective with
a Zeiss X6 compensating ocular or a Spencer 16 mm. apochromatic
objective with a Spencer X10 compensating ocular, or their equivalents,
being used to obtain the proper magnification.
PLATE 13
(A)—Spores and fragments of filaments of mold from decaying sweet pepper.
After Howard
in
UJ3J)uL.
Year Boob
1011.
(B)—Yeasta and bacteria from de-
caying tomatoes.
(O—Rod-shaped
tomato pulp.
bacteria from
324