Freely-flowing powdered fresh baker's yeast preparation and method of producing it

A fresh baker's yeast preparation of greater stability is provided in which a hydrophobic additive which assists in the free flow properties of moist bulk materials, for example hydrophobic silicon dioxide, is added in from 0.01 to 5% by weight of yeast optionally a hydrophilic substance can be added for example hydrophilic silicon dioxide.

Baker's yeast is generally produced and marketed in two different forms of 
vastly different water content, namely as fresh baker's yeast (residual 
water content approx. 65 to 75% by weight) and as dried baker's yeast 
(residual water content approx. 10% by weight or less). 
Fresh baker's yeast is a yeast composition of a plastically-firm 
consistency from which extra cellular water has been substantially removed 
by mechanical extraction. It is made up for retail in various forms. Best 
known is the compressed yeast which is shaped into pound pieces or small 
domestic cubes. Also known is fresh baker's yeast in lump or coarsely 
granulated form; known as "bagged yeast", this form is preferred by many 
large scale users. When fresh baker's yeast is made up for sale in this 
way, it is necessary, prior to using it for baking purposes, to suspend it 
in water to make sure the lumpy moist yeastbecomes finely dispersed and 
will blend evenly with the flour ("dissolving" the yeast). 
In relatively rare cases, fresh baker's yeast is also marketed in the form 
of a liquid aqueous cellular suspension known as "yeast milk" or "liquid 
yeast". However, the fact that it spoils so rapidly when stored, along 
with other disadvantages, impair this form of presentation. 
In contrast, dried baker's yeast is a yeast cell composition of more or 
less finely granulated or lump form which has been completely dehydrated 
under gentle conditions. Prior to being used for baking, most types of 
dried baker's yeast have to be reconstituted under special conditions with 
water or with aqueous solutions. Only a few types are "instant" in nature 
and can be added directly to the flour. 
The invention is based on the problem of providing a new form of packaging 
for the conventional mechanically drained fresh baker's yeast so that it 
is suitable for despatch purposes as well as offering advantages in terms 
of keeping properties and use for baking purposes, and also of providing a 
method of producing the same. 
A considerable disadvantage of fresh baker's yeast is the fact that it 
spoils relatively quickly when stored, its shelf life depending upon its 
water content. This spoilage is a consequence of the endogenous metabolic 
processes taking place in the yeast cells and which, after certain 
intracellular reserves have been consumed, lead to autolysis of the yeast. 
Naturally, since the endogenous metabolic rate depends upon the 
temperature, the yeast spoils more rapidly at higher temperatures than at 
low temperatures. As far as possible, therefore, fresh baker's yeast is 
transported and stored in a refrigerated state. 
The time before onset of autolysis at a specific storage temperature used 
in the past to be taken mostly as a measure of the storage life of a fresh 
baker's yeast. However, it is now known that even while the yeast is being 
stored, its leavening force diminishes more or less rapidly and is almost 
completely lost at the onset of final spoiling, i.e. autolysis. 
Consequently, measurement of the leavening force of yeast at intervals 
during storage provides a very accurate measure of the durability of a 
fresh yeast. The figures contained in the ensuing part of the description 
concerning durability of yeast are based on measurements of leavening 
force during yeast storage. 
The leavening force was measured in a standard dough using a fermentograph 
(Messrs. Brabender, Duisburg) using the method advocated by A. Harbrecht 
and R. Kautzmann (Die Branntweinwirtschaft 107; 507-512, 536-545, 558-562; 
1967). 
Many attempts to improve the keeping properties of fresh baker's yeast are 
known from the literature. Additions of specific hydrophilic water binding 
agents have been suggested with the object of reducing the water content 
of the yeast cells, so retarding those endogenous metabolic processes 
dependent not only upon the temperature but also upon the effective water 
activity, so improving the keeping properties of the yeast. However, none 
of the proposals made so far in this direction has succeeded in becoming 
accepted in practice. It is true that the durability of the yeast can be 
improved by the addition of hydrophilic water binding substances in the 
relatively large quantities known from the literature (added quantities of 
up to many times the weight of the fresh yeast), but the degree of 
leavening force of these yeast preparations is diminished in accordance 
with the proportion of weight of additives. 
However, the intended purpose is not achieved by adding small quantities of 
the hydrophilic water binding substances already suggested for fresh 
baker's yeast. It can be readily demonstrated that for example an addition 
of 15% starch or locust bean flour to fresh baker's yeast does not 
significantly improve the keeping properties of the yeast. 
According to the invention, it has been found that the durability of fresh 
baker's yeast is particularly ideally improved by intimate blending with 
relatively small quantities of finely powdered hydrophobic substances 
which are normally used in industry as lubricants to improve the free flow 
properties of hygroscopic bulk goods which tend to agglomerate. At the 
same time, the moist fresh baker's yeast is converted to a fine 
freely-flowing powder which can be added directly to the flour in a 
measured quantity when preparing dough for baking. Surprinsingly, the 
durability-enhancing effect is reinforced by admixture of hydrophilic 
water binding substances in quantities which by themselves produce no 
significant improvement in yeast durability nor produce a freely-flowing 
powder. 
Basically, any agents which improve the free flow of hygroscopic bulk 
materials are suitable as hydrophobic substances. For this purpose, 
various sustances are used which, as the temperature of application, are 
present in solid, as far as possible finely comminuted and highly disperse 
condition, having a water-repellant character. These substances become 
deposited around the particles of the particular bulk material concerned 
and so make it readily pourable. 
According to the invention, in principle all known substances of this 
nature are suitable (.e.g. talcum or specific salts of higher fatty acids, 
such as magnesium stearate). Hydrophobic silicon dioxide in a disperse 
colloid state has been found to be particularly suitable. Such a product 
is marketed for example under the name "Aerosil R 972" by Messrs. Degussa 
of Frankfurt. Where the use of magnesium stearate and similar salts of 
higher fatty acids is concerned, nevertheless, it is important to remember 
that they have a readily alkalising action. In order to avoid any possible 
damage to the yeast which might result from this, it is necessary in such 
cases to add appropriate quantities of organic acids, such as for example 
citric acids, to neutralise the alkalising action. 
The quantities of the said hydrophobic substances which have to be added to 
achieve pourability in and to improve the durability of fresh baker's 
yeast are small. According to the residual water content of the fresh 
baker's yeast used, it is sufficient to add 0.01 to 5% by weight (related 
to fresh yeast) in order to achieve the desired effects. Preferably, 0.2 
to 1% by weight should be added. Table 1 shows the quantities dependent 
upon the residual water content of the yeast. 
Table l 
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Quantities of additives sufficient to produce the fresh 
baker's yeast preparation according to the invention, as 
a function of the residual water content in the fresh 
baker's yeast 
Quantities to be added in % by weight 
Residual water 
(related to fresh yeast 
content of Hydrophobic 
untreated substances Hydrophilic substances 
yeast (% by (e.g. Aerosil Organic 
weight) R 972) (Aerosil 200) 
swellers 
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72 1.0 5.0 10.0 
70 0.5 2.5 5.0 
67 0.3 1.0 3.0 
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As hydrophilic additives to enhance the durability-improving effect and 
with the action of saving on the quantities of hydrophobic substances 
which have to be added, it is basically ideal to use all those substances 
which have a capacity for water absorption and which do not harm the 
yeast. For example, these include the majority of known water binding 
organic swellers such as possibly swelling starch, alginate or locust bean 
flour. But also other substances have been found suitable; particularly 
favourable is hydrophilic silicon dioxide marketed for example under the 
trade name "Aerosil 200" by Messrs. Degussa of Frankfurt. 
The hydrophilic organic swellers should be added in quantities of 1 to 15% 
by weight (related to fresh yeast), and preferably 3 to 10% by weight. 
When hydrophilic silicon dioxide is used, it is sufficient to add 0.2 to 
10% by weight. Preferably 1 to 5% by weight are added. 
Procedurally, the coarse or lumpy yeast composition mechanically drained in 
rotary vacuum filters or filter presses such as are used in conventional 
fresh baker's yeast production, is placed in a commercially available 
blender in which the above-mentioned additives are converted to a 
freely-flowing powder by mechanical blending; particularly the hydrophobic 
substances greatly assist the blending process. Therefore, relatively 
simple blenders having slowly rotating blades or planetary mixers may be 
used. As far as possible, long mixing times or the application of high 
mechanical pressures should be avoided, since otherwise -- as with all 
pourable but moist bulk materials -- lumpy aggregates will reform. 
Suitable blenders are for example the VRIECO horizontal spiral screw mixer 
(Messrs. Wendel KG, Budingen) or batch mixers of type FM or FKM (Messrs. 
Lodige, Paderborn). For a simple but nevertheless convincing experiment to 
establish the effect of this invention, it is also sufficient to place a 
fresh baker's yeast (particularly a "bagged" yeast) into an ordinary 
laboratory mortar, add one of the above-mentioned hydrophilic and 
hydrophobic substances and then to mix the composition with the pestle of 
the mortar and without applying any great force. 
Comminution of the fresh baker's yeast preparation in the blender should 
preferably be carried out down to a maximum size of approx. 0.8 mm 
particle diameter. By screening out the coarser particles and returning 
them to the blender, this is relatively easy to achieve. The individual 
size of the yeast preparation particle naturally influences the blending 
properties of the preparation with the flour when the yeast is used for 
baking. The smaller the yeast particles are, the more regularly and finely 
they can be blended with the flour when the dough is being prepared. 
However, this is not a deciding factor because by reason of the high shear 
stresses which arise when dough is being kneaded, the now water-repellant 
yeast particles are further comminuted. Consequently, when the yeast 
preparation according to the invention is used for baking, in spite of the 
fact that it is mixed with the flour directly and without any previous 
"dissolution", an equally good leavening force and equally good texture 
will be achieved when compared with untreated starting yeast, normally 
added to the dough after being "dissolved". 
When a fresh yeast preparation prepared according to the invention is 
viewed under a stereoscopic microscope, with illumination, a unique effect 
is observed. It is possible quite clearly to differentiate between heavily 
water-bonded hyaline particles and other yellowy-creamy particles 
containing mainly yeast. If by means of stereomicroscopic observation, a 
number of the clearly visible hyaline particles are picked out from the 
yellowy-creamy particles, then a chemico-analytical check will show that 
treating the fresh baker's yeast in accordance with the invention has 
produced a compartmentation of the water. The majority of the 
extra-cellular water balanced with the intra-cellular water is separated 
from the yeast particles and both types of particles are obviously 
enclosed by the hydrophobic additive. The hydrophilic additives involved 
in the water compartmentation process are preferably located in those 
particles which are rich in water. 
The figures given in Tables 2 and 3 show the improvement in keeping 
properties of fresh baker's yeast, achieved by the method of the invention 
.

The invention will be explained in greater detail hereinafter with 
reference to the following non-limitative examples. 
EXAMPLE 1 
100 g lump fresh baker's yeast ("bagged yeast") with a water content of 70% 
by weight, are placed in a porcelain mortar of normal laboratory type and 
2.5 g hydrophilic silicon dioxide (Aerosil 200, Degussa) and at the same 
time 0.5 g hydrophobic silicon dioxide (Aerosil R 972, Degussa) are added, 
whereupon the materials are mixed by hand using the pestle and without 
applying any considerable force. Within a few minutes, the mixture assumes 
the state of a very fine and free-flowing powder. 
In comparison with the starting yeast, the fresh baker's yeast preparation 
which is produced in this way exhibits a substantially improved durability 
when stored. The leavening force and the durability of the preparation are 
shown in Tables 2 and 3. When used for baking purposes, the fresh baker's 
yeast preparation is added directly to the flour while the dough is being 
prepared. 
EXAMPLE 2 
2 kg fresh baker's yeast with a moisture content of 70% by weight and 50 g 
hydrophilic silicon dioxide (Aerosil 200, Messrs. Degussa) are mixed for 1 
minute in a blender type PMA 20 made by Messrs. Alexanderwerk of 
Remscheid. After addition of 10 g hydrophobic silicon dioxide (Aerosil R 
972, Messrs. Degussa), blending is resumed for another minute. During the 
mixing process, the preparation assumes the form of a very fine and 
freely-flowing powder. The leavening force and durability as well as the 
baking application are in accordance with the fresh baker's yeast 
preparation produced according to Example 1. 
EXAMPLE 3 
100 kg fresh baker's yeast (moisture content 70% by weight) are mixed with 
5 kg swelling starch and 0.7 kg hydrophobic silicon dioxide for 1 minute 
in a mixer operating on the centrifugal and rolling process and made by 
Messrs. Lodige of Paderborn, type FM 300 D. The mixture is then screened 
and that fraction of less that 0.8 mm mesh is used as the end product. The 
fraction larger that 0.8 mm is returned to the mixture for further 
comminution. Leavening force and durability of the preparation are shown 
in Tables 2 and 3. 
The fresh baker's yeast preparations according to the invention are 
characterised not only by excellent durability and storage capacity, but 
can also be despatched over considerable distances by virtue of the way in 
which they are presented. 
Table 2 
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Durability of the fresh baker's yeast preparation according 
to the invention when stored at 25.degree. C. compared with the 
starting a fresh baker's yeast used 
Storage 
Leavening time (weeks) 
force before 
1 2 3 
commencement 
Leavening 
of storage 
force (as % of 
(ml CO.sub.2 /2 h) 
starting value) 
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Untreated yeast 
(with 30% dry yeast 
substance) 1280 80 20 -- 
Yeast + 0.5% Aerosil R 972 
+ 2.5% Aerosil 200 
1240 92 78 56 
Yeast + 0.7% Aerosil R 972 
+ 5.0% swelling starch 
1205 84 45 27 
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Table 3 
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Durability of the fresh baker's yeast preparation according 
to the invention when stored at 6.degree. C. compared with the 
starting fresh baker's yeast used 
Storage time (weeks) 
8 16 24 32 40 
Leavening force 
(as % of initial value) 
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Untreated yeast 
(with 30% HTS) 80 40 8 0 0 
Yeast + 0.5% Aerosil R 972 
+ 2.5% Aerosil 200 
90 78 69 65 60 
Yeast + 0.7% Aerosil R 972 
+ 5.0% swelling starch 
91 75 59 47 36 
(Leavening force before commencement of storage as in Table 
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1)