Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention concerns the packaging
of bakers yeast and aims at providing packages of such
yeast, e.g., in free flowing form, in which when stored
under refrigeration the yeast retains essentially its
physical and leavening characteristics over extended
periods of time.
Yeast which is to be used for baking purposes
is a product based on any of the strains of the species
Saccharomyces cerevisiae. There are many strains of
yeast that are included within this species, differing
from each other, among others, in osmotolerant
characteristics, ability to ferment various sugars,
resistance to dehydration, etc. A yeast product based
on any of these strains is produced commercially in a
series of fermentations or stages. The yeast is grown
under aerobic conditions by the addition of large volt
uses of air to the growth media. Carbohydrates, in the
form of molasses, and nitrogen sources, in the form of
ammonia, are continuously incorporated into the growth
media, especially in the last stages of propagation. The
phi temperature and solute concentration of the growth of
media are maintained within ranges where optimum growth
the yeast occurs. At the conclusion of the last propagation
stage, the yeast is separated from the other dissolved
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constituents of the growth media by centrifugation and
a number of washing cycles. Yeast at this stage, at
about 204 solids content, is a tan colored liquid and
known in the art as liquid or cream yeast. Cream yeast
is converted to a plastic or solid consistency by vacuum
or other filtration procedures. Such yeast product is
known in the art as compressed yeast containing approximately
30~ solids and may be molded or extruded into blocks or
cubes in which form it is supplied to bakers or for
household use.
Another form of yeast product provided to the
baker is bulk yeast. This product, almost always at a
solids level substantially above 30%, is granulated and
provided to the baker as is or treated with a minor amount
of drying agent intended to preserve the free flowing
characteristics of this type of yeast.
Still another yeast product available to the
consumer is referred to in the art as active dry yeast.
The initial processes involved in the production of this
product are those described for compressed or bulk yeast
production, a Saccharomyces cerevisiae strain known as
Boos No. 23 being generally used. The issue classification
is as per publication by Schultz and Akin in "Archives of
Biochemistry", Vol. 14; p. 369 (August 1947). Prom a
suitable compressed or bulk type yeast product obtained
from this strain, active dry yeast is obtained by any of
several processes known in the art. or example, the
compressed yeast can be converted into spaghetti form and
dried on a moving belt under controlled temperature and
time conditions.
Fresh, compressed or bulk yeast is sold principally
to bakeries. The household consumer has two types of yeast
products available to him. They are fresh compressed
yeast packages or cubes, wrapped in aluminum foil, or
active dry yeast, packaged in air, vacuum, or under inert
gas conditions.
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The fresh compressed yeast cube, known in
tile art as Household Yeast, is distributed as a
refrigerated item. This product has a shelf life of
about 4 to 6 weeks under storage conditions generally
referred to as cool and dry. To achieve this kind of
storage characteristics the yeast has to undergo special
treatment in all stages of its preparation, especially
before filtration and packaging. Also, the packaging
material generally an expensive aluminum foil laminate
has to be especially treated to minimize the tendency of
mold development on the surfaces of the yeast cube. This
kind of product, being in cake or block form, has the
additional disadvantage of having to undergo dispersion
before it can be added to the flour in home baking. The
product suffers also from other shortcomings such as loss
of weight and discoloration if not properly wrapped.
The development of an active dry yeast product
came against the background of the disadvantages exhibited
by the household yeast package, and aimed at providing a
better product. And indeed the active dry yeast type product
has a longer shelf life and has no mold or discoloration
problems. The active dry yeast has, however, other
inherent problems. For one, it is less active than fresh
yeast. Moreover, it has to be dehydrated under controlled
temperature convictions before it can be used in the
baking process, and this can become a major burden to the
consumer when attempting to bake yeast leavened goods in
a kitchen. Additionally, to achieve a reasonable room
temperature shelf life, the yeast may have to be packaged
in expensive material such as aluminum foil laminates under
inert gas conditions When adding to this the cost of a
very demanding drying procedure, there results a very
expensive product for the household consumer.
It is thus seen that both of the two kinds of
commercially available yeast products have serious drawbacks
and are far from satisfactory.
Bakers yeast, e.g. free flowing, fresh bulk
yeast, would be an ideal product for, among others, the
household consumer. For the consumer to enjoy all the
possible benefits of such a product it would have to
come to him in a package which ensures for the yeast
the following characteristics:
1. A reasonable stability to rough handling.
2. A relatively long refrigerated storage stability.
3. Retention of physical properties, even under
stacking or pressure.
4. No discoloration of the product due to partial drying
or oxygen contact.
5. Total or near total prevention of so-called respiration,
i.e. stop the penetration of oxygen into the package.
6. Protection of the yeast product from mold development
and reduction to a large extent of the invasion of
contaminating microorganisms.
7. Preservation to a large extent of the initial
leavening activity of the yeast product.
B. Ready availability in a form in which it can be
added directly to the flour without requiring a
cumbersome resuspending stage that is necessary with
the household cube or active dry yeast products.
Bakers yeast is, however, a potentially
problematical product. It comprises a mass of living
yeast cells having varying amounts of extra-cellular water
in the interstitial spaces between and surrounding the
cells. Water is also the largest component of the yeast
cell and is referred to as intracellular water. The feel
or appearance of compressed or bulk yeast is largely
determined by the relationship between the intracellular
and extra cellular water in a particular yeast product
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preparation. Obviously, the relative dryness or
wetness of a yeast product will affect the tendency of the
yeast to stick or coalesce and therefore cause a
deterioration in its free flowing characteristics.
Bulk yeast, being in a fine granulated form,
provides a relatively large surface area for atmospheric
oxygen to interact with the yeast. The process is called
respiration and its results are the generation of water,
heat, and other products. It is this generation of
extra water during handling and storage that can
ultimately partially or totally destroy the free flowing
characteristics of the yeast product. US. Patent
No. 4,232,045 provides a partial remedy to this problem.
It teaches the incorporation into the granulated yeast
of a drying agent that will tie up some of the water
that may be generated by the process of respiration. A
bulk yeast produced by the teaching of that patent will
indeed have an improved capacity to retain free flowing
characteristics over extended periods when packaged in
especially designed polyethylene lined bags and held under
refrigerated conditions. Because of the nature of the
package, respiration occurs however, end ultimately
sufficient water is generated, overland above the absorption
capacity of the drying agent, leading to a reduction of
the free flow capacity, discoloration, and loss of
leavening activity. A similar approach is also disclosed
in laid open German patent specification No. 26 19 348.
In British Patent No. 966,984 a partial solution
is provided to tackle the respiration aspect of granular
(bulk yeast. In accordance with the teachings therein
granular yeast is packaged in polyethylene (or similar
material) which slows down the rate of oxygen penetration
into the bag while permitting carbon dioxide generated
in consequence of respiration and auto fermentation,
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to diffuse Jo the outside. Pro better carbon dioxide
discharge a special OpeniJ1g is provided in the bag.
It has, however, turned out that in practice oxygen still
finds its way into the yeast, resulting in respiration
or generation of water.
The problem of respiration could not be solved
by simply packaging yeast in hermetically sealed containers
or under any other anaerobic conditions, thereby to
prevent penetration of oxygen, since the prior art teaches
that strict anaerobic conditions are detrimental to the
packaged yeast product. Thus, in the book "The Yeasts"
(S. Burrows - 1970), in the chapter dealing with the
keeping quality of compressed or bulk yeast it is stated,
among other things, "oxygen and carbon dioxide concentrations
in the immediate vicinity of the resting cells appear to
be of considerable importance ...". It is further stated
that granulated compressed yeast is difficult to store and
that " ... a certain amount of ventilation appears to be
necessary, possibly to allow a reduction in carbon dioxide
by diffusion.". Furthermore, from a paper presented by
~ajamaki Factories of the State Alcohol Monopoly, Alto,
Finland, at the Yeast Symposium held in-France in 1978,
it follows that anaerobic storage conditions are very
deleterious to the quality of the yeast as compared to
better quality if oxygen is present during storage.
In accordance with the invention there is
provided a method of preparing a packaged yeast product,
wherein fresh free-flowing bulk yeast is introduced into a
pliable bag whose oxygen permeability at 1 elm. pressure
differential across the material does not exceed about
1000 cm3/m2 per day and whose carbon dioxide permeability
at 1 elm. pressure differential across the material does not
exceed about 4000 cm3/m per day, the amount of yeast in
the bag being so dosed that the bag is not full to capacity,
the so filled bag is sealed hermetically and is then left
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a-t a temperature within the range of 0-20C to enable
-the occurrence of auto fermentation without affecting
deleteriously yeast quality thereby to produce carbon
dioxide and inflate the bag.
As a result of the inflation there develops
a carbon dioxide protective cushion around the grant-
fated bulk yeast. In this way the yeast is protected
against rough handling and squeezing during trays-
partition and storage, whereby the free flowing
properties of the yeast are retained.
Preferably, air present in the head space of
the bag is expelled as far as possible by squeezing
before the bag is sealed.
Upon the completion of the inflation the
yeast in the sealed bag is under what may be termed
anaerobic conditions characterized by the presence of
mainly a carbon dioxide atmosphere. As already
explained above, the prior art teaches that yeast may
not be stored under anaerobic conditions since under
such conditions the leavening capacity is significantly
reduced. The prior art further teaches - see for
example British patent specification No. 966,984 and
"The Yeast" by S. Burrows referred to above - that
carbon dioxide must be continuously removed from
stored yeast. It was therefore completely surprising
to discover in accordance with the present invention
that by storing fresh, free flowing bulk yeast in
sealed bags under a carbon dioxide atmosphere, the
yeast retains essentially its free flowing character-
is tics and its leavening strength for extended periods
of time.
The degree of inflation of the bag that is
required for the purpose of the present invention is
not critical as long as it is sufficient to produce a
protective cushion as specified. In practice, full
inflation of the package is as a rule not required
For example, in a package configuration of 1 g of
yeast to four volumes of _ _ _
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package size, it will be quite sufficient to generate
only 2 ml of carbon dioxide per gram of yeast. For the
generation of such relatively small amounts of gas it
is as a rule not necessary to warm the packaged yeast
above the packaging temperature and it is sufficient
to cool the yeast down to storage temperature - as a
rule about 5-10C - at such a rate that sufficient
carbon dioxide develops.
The degree of inflation is obviously directly
affected by the rate of auto fermentation by the yeast,
which in turn is dependent on the temperature of story
age. Thus, any particular yeast strain grown under a
particular set of propagation conditions, to a specific
nitrogen and phosphorous content, will have a predict
table and known auto fermentation profile at a given temperature. It is accordingly possible to alter any
of the above to produce a yeast that has a suitable
auto fermentation profile.
The art also teaches other ways by which one
can affect a change in the auto fermentation profile of
a particular yeast product Thus, the treatment prove-
dune described in US. Patent 4,008,335 is quite suit-
able for the purposes of the present invention.
The handling temperature during the pack-
aging will as a rule be within the range of 10-20C
and the cooling down period may typically be from 24-48
hours.
There is no criticality as to the relative
proportions between the volumes of the bag and the pack-
aged yeast. In this context volume of bag means the volume of water required to fill it to capacity when
empty, and weight ratios of yeast to bag volume of 1:27,
have been found to produce satisfactory results. How-
ever, such packaging would be wasteful and as a rule
a weight ratio of yeast to bag volume = 1:4-1:6 is
preferred.
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g
The material used for making pliable bags
whose permeability to oxygen and carbon dioxide is as
specified can be of any kind -that is inert to the pack-
aged product. For example, bags made of plastic polyp
ester sheets, possibly reinforced with small amounts
of polyethylene, may be used to advantage. Other
examples are bags made of polypropylene or aluminum
foil, and there are of course many others.
Typical plastic material sheets produced by
Kibbutz Negba, Israel, have the following permeably-
ties:
Gas Permeability (cm3/m? day, bar*)
Oxygen Carbon dioxide
Polyethylene 1,700 8,500
Polypropylene 1,000 3,500
Polyester 100 450
* "bar" stands for a pressure difference of 1 elm.
It follows from these data that polyethylene
is unsuitable for the purposes of the present invention
while polypropylene and polyester are suitable.
As explained above, hitherto household consul
mews had at their disposal only either compressed yeast
or active dry yeast and either of these products have
their inherent disadvantages, the cubes or bars of come
pressed yeast having to be first dispersed in Waterloo the active dry yeast has to be dehydrated prior to
use for which specific conditions have to be strictly
observed. Free flowing bulk yeast is free of all these
disadvantages but hitherto had the disadvantage of having
a relatively short shelf life even under refrigeration
so that hitherto it could only be used in bakeries.
The invention provides for the first time free flowing
bulk yeast for household use packaged so as to have,
when stored under refrigeration, a relatively long
shelf life of 3 months or even more.
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Quite generally, the present invention pro-
vises maximum storage stability that any particular
yeast may have. Thus, for example, i-t is possible in
accordance with the invention to store and preserve
bakers yeast for household use which hitherto has not
been possible.
The invention is illustrated in the following
Examples without being limited thereto.
Example 1
This example describes the profile of a par-
titular yeast as regards its potential to produce car-
bun dioxide by auto fermentation and to the leavening
activity by the yeast product upon storage for differ-
en periods without refrigeration.
The yeast was propagated under normal condo-
lions to a composition of about 42~ total protein
(Kjeldahl) and 1.90~ POW. After centrifugation and
washing, 300 liters of cream yeast were treated with
20 liters of a saturated sodium chloride solution.
The treated liquid yeast was vacuum filtered to about
34 per cent solids, granulated through a plate contain-
in 2 millimeter diameter holes, and treated with four
per cent Aerosol 200 on a weight basis (a trade mark of
Degas A of the Federal Republic of Germany).
The packaging was in a polyethylene reinforced
polyester laminate of about 0.06 mm total thickness.
The actual formation of the packages, filling and heat
sealing was by hand. The sealed package containing 20
g of free flowing yeast was at about 18C when the test
series was started. The volume of the package when
empty (as measured by the volume of water that it
could hold) was about 550 milliliters. Table I sum-
marines the results.
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Table I
Initial --
Temperature Carbon dioxide Activity
Days of of storage generated retained,
5 storage average). .cc/gr %
.. _ _ .. _ _ . . . _ .. .. . _
1 17.8 4.4 100.0
12 17.8 7.7 86.2
16 19.4 12.4 77.7
19.4 13.8 55.4
23 20.0 18.0 42.4
Example 2
Yeast was propagated, filtered, treated with
Aerosol 200, and packaged as under Example 1. Two
package sizes, one of 170 milliliters volume and the
other of 550 milliliter volume, were willed each with
20 grams of free-flowing, fresh baker's yeast. The
results are given in Table II.
Tubule
* Leavening Activity
** Package Size
. .
milliliters 550 milliliters
Fresh 1945 1945
After 3 months at
5C 1410 1420
* Volume of carbon dioxide produced in two hours in
a flour dough containing initially 10% added sugar.
** The size refers to the empty package when filled
with water. In actuality, the package designated
as "170" had only a total volume of 70 milliliters;
while the package designated "550" had a total
volume of 128 milliliters after two weeks at 5C
(as measured by immersion of sealed yeast package
in water and determining the total volume of water
displaced). These relative volumes did not change
on further storage at 5C.
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Example 3
This example compares the stability of the
package produced in accordance with the invention to
the stability of a package that had a pun pro-
vision for the diffusion of carbon dioxide to the out-
side according to the teachings of British Patent No.
966,984.
The yeast was propagated as in Example 1,
but this time to a protein composition of 41.9% and
POW of about 1.70%. The filtered yeast contained
about 34.7% solids. After treating with 2% Aerosol
200, the yeast was packaged in polyethylene-polyester
film as in Example 1, but this time in a package that
contained 25 g of free-flowing yeast in a total package
lo volume of about 100 milliliters. The yeast was package
Ed on a commercial packaging machine supplied by Rouse
of Barcelona, Spain, model 1214 T. The yeast packages
were stored at 15-20C and the observations made after
14 days of storage are recorded in Table III.
Table III
Activity
retained
%. Flow property
Start fresh) 100 Free flowing
After.one..week..
. _ _
Sealed package 100 Free flowing
Pin-hole in package 79 Formation of
. small lumps
After.two.weeks
Sealed package 90 Free flowing
Pin-hole in package 57 Gummy
consistency
It is seen from the data in the table that
the flow properties upon packaging and storage in
accordance with the invention are significantly
superior to those according to British Patent No.
966,984.
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Example 4
This example illustrates the potential of
storage stability that our invention may impart to
free-flowing, fresh baker's yeast under various
-temperatures.
The yeast was propagated and treated as under
Example 3 and stored under the various storage condo-
lions as listed in Table IV. Before storage, the
temperature profile of the yeast during preparation
10 and packaging was:
After filtration and extrusion 13C
After treatment with Aerosol 14 C
After two days at 0C yin bulk) 2C
After packaging and handling 17C
The storage series started with the yeast being at
17C and having generated about one ml of carbon
dioxide per gram of yeast at this point.
Table IV
Activity retained - %
20 Days of storage Storage temperature - C
lo 15 20
7 100100 100 100
14 100 97 90 68
21 100100 23 18
2528 100 97 0 0
100 92 0 0
93 84 0 0
Example 5.
.
This example illustrates the superiority of
a polyester laminate over polyethylene which has
inherently a certain degree of permeability to oxygen
and carbon dioxide.
The yeast was propagated, filtered, treated
with Aerosol 200, and packaged as under Example 1.
Two types of packaging materials were compared.
Polyethylene film alone was compared to a laminate of
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polyester. In the first case 20 g of free-flowiny,
fresh baker's yeast was sealed in a polyethylene
package with a potential volume ox about 170 ml., the
polyethylene being of 0.05 mm thickness. In -the second
instance, 20 g of similar yeast was sealed in a polyp
ester laminate with a potential volume of 5S0 ml., the
laminate being of 0.06 mm total thickness. No attempt
was made to squeeze the head space air out before heat
sealing. In both cases the temperature history of the
yeast was identical and thus:
Extruded yeast 13C
After treatment with Aerosol 16C
After packaging 18 C
The storage started at 18C and was at room conditions
in a temperature range of 15-20C. The results were:
After 12 days at 15 to 20C
Polyester
Polyethylene laminate
_
Activity retained, 57 88
20 Appearance Gummy with Free-flowing
putrid odor and fresh
smelling
Example 6
This example compares the permeability
characteristics of three different plastic materials
in terms of the degree of head space inflation of the
yeast package as a function of storage temperature.
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Table V
StorageInflation.of Available Head Space - %
Temperature Packaging Material
and Time ...... Polyethylene Polypropylene Polyester
5 Attica
. . .
2 months 0 8 31
Attica
5 days 14 24 83
10 days 0 20 97
1017 days 0 20 burst open
Attica
2 days 19 44 59
3 days 22 52 90
5 days 3 44 burst open
157 days 19 64 burst open
It is seen from Table V that polyethylene is
unsuitable because it allows the COY generated by the
yeast to readily escape to the outside.
Example
.
This example compares the results obtained
upon storage of yeast in polypropylene and polyester
bags in accordance with the invention.
Table VI
Polypropylene Polyester
Activity Activity
Days.at.16C retained,.%. retained, %
.. ...
96 100
7 90 87
12 92 86
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Example 8
. . .
This example compares -the results obtained
in accordance with the invention with two kinds of
yeast.
Table VII
* Inflation.- %
Type of Yeast
Days Attica Untreated Treated **
3 55 21
26
7 burst open 69
- * A polyester laminated package, with an available
volume of about 240 ml, was heat sealed with
about 50 grams of yeast in it.
** Treatment of liquid yeast, prior to filtration
and further handling, was as per US. Patent
4,008,335.
Example 9
This example shows the leavening activity of
yeast packaged in accordance with the invention in
bread dough formula after different storage times at
5C.
Time.of.storage at 5C Activity retained, %
. _ . _ . . . _ . . .
4 months 87
25 5 months 84
6 months 74
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