Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~9~35
-- 1 --
FREE FLOWING FROZEN PARTIC[JLATE YEASTS
AND USE OF THESE NOVEL YEASTS IN FROZEN DOUGHS
The inven-tion relates -to a novel form of
baker's yeasts, combining the advantages of fresh
yeasts and dried yeasts. It relates to frozen yeast
having a dry ma-tter conten-t be-tween 30 and 85%, prefer-
ably of at least 70~ and more preferably be-tween 72 and
80% in the form of free-flowing par-ticles incorporable
directly in doughs. The inven-tion also relates to -the
process for ob-taining said novel yeasts and -their use
in -the manufacture of ~rozen doughs.
STATE OF THE ART
Baker's yeasts are marketed essentially in
-two forms:
. in the form of fresh yeas-t having a dry
ma-tter content be-tween 27 and 35% occurring in blocks
of 500 g or 1 kg, or in divided form (bulk yeas-t or
crumbled yeast) in bags of 11 to 25 kg. So that fresh
yeast remains in divided form and does not reagglomer-
ate, it is often necessary to add to it a certain
number of additives as indicated in British paten-ts
25 1,530,866 and 1,560,478 or European patent application
No. 0,]53,117. This Eresh yeast preserved a-t ~C must
be used at the latest wlthin one month an~ preferably
within a period of two weeks. In practice, the storage
conditions oE Eresh yeasts are rarely ldeal and this
3Q reference temperature of 4C is poorly respected.
Besides fresh yeast which has to be preserved at -~4C,
there exists marginally a commercia:Lization oE fresh
yeast in blocks o~ 500 g or 1 kg in frozen form. The
freezing obligatorily results in blocks of yeas-ts; the
bulk form divided yeast even wi-th additives, agglomer-
.J~' ~
3~i;
a-tes in-to blocks on freezing. This yeas-t must be
thawed to be incorpora-ted in doughs and used very
rapid].y after thawing. The freezing-thawing -treatment
is sligh-tly penalizing for the yeast and -the use of
frozen yeasts in block form is inconvenien-t.
. in dried yeas-t form with a-t least 92% of
dry matter. Active dry yeasts have the drawback of
having lost a part of their gassing power during the
drying and the membranes of the yeast cells are more or
less altered. They have the advantage of long preser-
vation, the best performing instan-t dry yeasts packaged
under vacuum or in neutral gas have a loss of fermen-
tative activity or gassing power of the order of 1% per
month at 20C. These dry yeasts mus-t always be re-
hydrated in a dough or in a l.iquid a-t at least 16C.
The prior art illus-trated by U.S. patent
3,089,774 comprises an attempt to prepare a yeast
having an intermediate moisture content, bu-t this
intermediate humidi-ty yeast is not being produced, a-t
least in Western countries (Yeast Technology 1973, Reed
and Peppler, page 94); its preservation properties are
not sufficiently greater than those of fresh yeasts
having about 30% of dry matter, preserved a-t +4C. In
addition these yeasts wi-th intermediate humidity are
very sensitive to temperature rise.
DESCRIPT.LON OF THE :[NVENTION
-
The invention consists in :Ereezing by fluid-
ization a dividecl bakerls yeast, so as to bring down
the yeast pa:rticles :Erom a temperature equal to 0C or
positive to a temperature between -5C and -30C, pref-
erably to -:L8C or -20C in a time comprised between 5
m:inutes and severa:L hours, for example between 7 and
120 minutes or between 10 and ~0 minu-tes.
The freezing by fluidization in a flow oE air
/ `~
i~9~,,f~
or oE neutral gas between -10C and -~0C, preferab:Ly
between -20C and -~0C and still more preferably be-
tween -18C and -30C, permits, on the one hand, rapid
heat transfer between the gas and the solid (the yeast
particles in a fluidized bed) without resor-ting to very
low tempe.ratures destructive of the yeast and, on -the
other hand, the individualization of the particles
which do not become reagglomerated. It is this latter
characteristic of the fluidization which is the most
interesting, since the yeast easily supports a slow
drop in tempera-ture and since i-t is preferable that
freezing is not too rapid.
This process can, if need be, be applied to
fresh compressed baker's yeasts having a dry matter
15 content between 30 and ~0%, preferably of at least 35%,
produced so as to be non-sticking and hence to be
fluidizable without agglomerating. Great care must be
taken in the design of -the fluidized bed freeze a.ppa-
ratus and in the operations of fluidiza-tion of these
fresh yeasts so as to obtain well individualized parti-
cles. The freezing mus-t not be -too rapid, the drop in
temperature when the temperature is lower than 0C must
not be more than 1C per minute. The products obtained
will still have a tendency to coalesce into clumps or
lumps and even to agglomera-te completely, which is a
considerable drawback.
This process applies preferentially to pre-
dried yeasts which do not present any difficulty in
fluidlzation. The pre-dry:ing w:ill also have the advan-
tage of reclucing the cost of storage and of transpor-
tation of these .Erozen yeasts due to the fact of their
lower weights. Pre-drying to at least 72% and prefer-
ably at least 7~ of dry matter will yuarantee against
all risk of coalescing into clumps ln packages and will
make the yeast particles remain perfectly free-flowing.
- r~
-- 4 --
This pre-drying can be conducted until -the
appearance of degradation of -the cell membranes due -to
the fac-t of the elimination of internal water from -the
yeast cells. I-t must never exceed 85% of dry matter
and preferably it will be continued up to about 77% of
dry matter, that is to say in order to obtain between
74 and 80% of dry matter.
The pre-dried baker's yeast having a dry
matter content comprised be-tween 70 and 85% must be
cooled as quickly as possible until a temperature com-
prised between -1C and +4C, as yeasts having these
dry matter contents incline to become heated very
quickly and they should not be left at temperatures
higher than 15C. Furthermore the freezing speed of
-the yeast is not a critical parameter provided it is
not too rapid. In other words, as soon as -the said
speed is longer than about 5 to 10 minutes, there is no
difference in the properties of the resulting yeast if
the drop in temperature from 0C to -20C takes 10
minutes or 12 hours.
The freezing in a fluidized bed of yeast
pre-dried to a dry matter content between 70 and 85%,
preferably between 72 and 80%, hence of yeasts no
longer containing external water or weakly bound water,
considerably reduces the risk of crystallization which
can affect -the integrity of the cells.
I'he particulate :Erozen baker's yeasts in
their preferred :Eorm haviny a dry matter content
between 70 and 85%, pre:Eerably between 72 and 80% ancl
still more preferably between 7~ and 80%, have the
aclvantacJes:
. of beincJ easy to handle and to incorporate
or to disperse directly in the douyh wi.-thout prior
thawing,
. of preserving practically inde:Einitely the
- ;
!.
3~-~
properties of the ini-tial fresh yeasts, taken as they
come out of procluction.
The particulate frozen yeasts, according to
-the invention, are paxticularly advantageous for the
manufacture of frozen doughs in-tended to be preserved
several months, -then to be thawed, fermen-ted and baked.
Studies done in the Applicants' labora-tories have shown
that the manufacture of these frozen doughs requires,
to ob-tain bread-products having uniformly and repro-
ducibly the desired development, the use of yeasts richin reserve substances, particularly in trehalose and
having intact rnembranes. In practice, taking into
account the dlstribution circuits, fresh yeasts can
only be used several days after they leave the factory,
and often they have not been fully maintained at
4C, but rather at temperatures of the order of 10C.
Consequently, the results obtained after thawing the
doughs are heterogeneous and give poor bread-products.
The employment of a particulate yeas-t, frozen by :Eluid-
ization as soon as it has been produced, enables theuse of a yeast which has kept all of these properties,
without any alteration and hence these drawbacks to be
overcome. The use of said particulate frozen yeast in
frozen dough enables the obtaining of better and more
regular results giving satisfactory bread-products.
The :E:inely divided and free-flowing frozen
yeasts have the advantage of being directly incorpora-
ble or dispersable :in the cold doughs intended for
freeæing, w:ith the result that the yeasts will be all
30. the less actl.ve in this dough be:Eore its freezing, a
nil or very low activity of the yeasts before freezing
being very desirable.
For this purpose, it w:ill be interesting to
add the free flowing particulate frozen yeasts a-t about
77~ of dry matter -towards the end of kneading, just
soon enough for i-t. to be totally dispersed in the
dough. This late addition of particulate yeast at
about 77% of dry matter does not penalize the dough
development, contrary -to the late addition of fresh
compressed yeast having a dry ma-tter content of 30%, i.n
fact the water contained in the fresh compressed yeast
and which is necessary for the dough development, can
be added directly to the dough at the beginning of
kneading, since the free flowing particula-te frozen
yeasts are partially dehydrated.
It is to be noted that the finely divided
frozen yeasts, in their preferred form having between
70~ and 85% of dry matter, preferably between 72 and
80~, do not show significantly more excretion or
leakage in rehydration at low temperature than fresh
yeas-t having about 32% of dry matter -taken just after
its production and dispersed in the same medium, which
shows that their membranes are intact and forms their
interest in the manufacture of frozen doughs.
20. The yeasts frozen in a fluidized bed accord-
ing to the inven-tion are presented in -the form of par-
ticles of dimensions less than 3 mm. Preferably, the
frozen yeasts according to the invention having a dry
rnatter con-tent comprised between 70 and 85% of dry
matter are presented in the form of vermicel~i of dia-
meter less than 1 mm.
rrhe frozen yeasts accorcling to the invent:Lon
can if necessary conta:in the additives disclosed in
British patents 1,530,866 and 1,560,478 or in U.S.
patent ~,232,0~5 or in the European patent applica-tion
1.53,117; these add:itives may be for example silica and
its derivatives. rrhey may if necessary con-tain also
the additives ~Ised generally for drying like those
described in U.S. patents Nos. 4,328,250, ~,370,420 and
~,396,632 lncorporated by reference; these additives
J~,
3~
may be for example sorbitan monostearate, polyglycerol
esters or citric esters of mono- and diglycerides
and/or alginates, gums, cellulose deriva-tives. They
can also contain lactose, lactoserum or skimmed milk,
sorbitol, glycerol, gelatin, that is to say substances
known as having cryoprotective properties. The addi-
tion of these additives represents modified embodimentsof the invention but is in no way indispensable.
The frozen baker's yeasts, divided into par-
ticles oE dimensions less than 3 mm, according -to the
invention, are packaged in air or in neutral gas, the
packaging in neutral gas only being of interest if the
yeast must be preserved more than three months before
being used. The frozen and divided yeasts are packaged
in bags of 1 to 25 kg, constitu-ted of materials used
commonly :Eor packaging of frozen food, for example, for
frozen vegetables, such as polyethylene with vinyl ace-
tate, -this material comprising an aluminum sheet if -the
partic~llate frozen yeast is packaged in a neutral gas.
EXAMPLE 1
A fresh balcer's yeast is produced as indi-
cated from line 14 of page 5 of the European patent
published under No. 8,55~, or as indicated in Example 2
of U.S. patent ~,370,~20 or in the examples of the U.S.
patent ~,396,632.
A yeast haviny a dry matter content of 33'~
and contain:ing 7.3~ of nitrogen on dry matter is ob-
tained. To this yeast i5 added a :Eine emulsion consti-
30. tuted by so:rbitol esters or polyg:Lycerol es-ters in a
proportion of about 1.5~ with respect to the dry matter
oE the yeast. lt is extruded through a grid having
perforations of width 0.5 to 3 mm, preferably 0.5 to 1
mm, and it is dried to about 75 to 78~ of dry matter by
a particularly gentle or mild drying that is to say a
r
.L~.,
3~
drying where the -temperature of the yeast does not
exceed 35C and preferably 30C.
The yeas-t vermicelli having about 75 to 78~
of dry matter are transferred into a vibrated fluidizer
supplied with air at -25C by a refrigerator unit, the
whole being carefully heat-insulated or placed in a
thermostated enclosure.
In general, it is possible to employ a fluid-
izer of design identical with those used customarily
for the drying of yeasts by fluidization, the essential
difference being its supply wi-th air at a negative
temperature. The principle used is the same: -through
the solid product (-the particulate yeast) is made to
pass an ascending flow of a fluid (air at a negative
temperature, for example -25C) whose speed balances
the weight of -the solid product and will ensure expan-
sion of the layer of individualized and mobile solid
particles into a fluidized bed.
There is noted in the freezing in fluidized
bed an increase of the dry matter content of the yeast
particles comprised between 0 and 1~.
The yeast vermicelli are frozen between -18C
and -20C in abou-t 20 to 30 minutes and packaged on the
one hand in air, on the other hand in a neutral gas
after freezing.
These bags are kept at -20C; the gassing
power of the fresh yeast before drying and freezing and
of the particulate frozen yeast with about 77~ dry
matter as obtained is measured after 1 month, 2 months
and 3 months of preservation at -20C.
The fermentative activities or gassing powers
ob-tained, measured in the Burrows and Harrison Eer-
mentometer accordlng to the test AL disclosed in U.S.
paten-ts No. 4,370,420 or 4,396,632, remain for the
particulate frozen yeasts with about 77~ dry matter
:'~
~2~3~
kep-t i.n preserva-tion, within the range comprised be-
tween 97% and 101% of the value obtalned fro~ the same
amoun-t of dry mat-ter of fresh yeast wi-th 33% of dry
matter which has been used for obtaining -the above-
mentioned particulate frozen yeas-ts. No significant
loss of fermentative activity is observed.
The frozen yeas-t having a dry matter content
of about 77% and occurring in the form of vermicelli
remains fluid, that is to say that the particles of
short vermicelli are very easy to disaggrega-te and
hence to handle and -to use. They have a good free
flowability.
EXAMPLE 2
A frozen baker's yeast in short vermicelli of
diameter 0.5 to 1 rnm, having a dry ma-tter content of
about 77% is prepared as in Example 1. The starting
material is a fresh yeast having a content of about 7%
of ni-trogen with respec-t to dry matter and having a
con-tent of more than 15% of trehalose with respect to
the dry ma-tter. The frozen particula-te yeast obtained
is kept for 11 weeks at -20C.
During the preparation o:E the above particu-
late frozen yeast, a sample is taken of the yeast
having about 77% of dry matter be:Eore freeziny and -this
sample is kept for 11 weeks at -~4C.
An American commercial fresh yeast, mar]ceted
in -the form o:E 1 pound blocks is sampled shortly a:Eter
its production and it is transported by air to the -test
site at ~4C. This fresh yeast had at the time of the
test of the manufacture of frozen doughs disclosed
below, a dry matter content of 30~ and a content of
nitrogen with respect to dry matter of 9.1%.
A commercial instant dry yeast of good quali-
ty with 95~ of dry matter was also used.
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. 1'~
-- 10 --
These 4 yeas-ts are tested in a bread-making
trial of type U.S. White ~read, scheme No--time dough
from frozen doughs. The 4 yeas-ts are incorporated di-
rectly by blending with the flour, which is very penal-
izing for instant dry yeast which will find itself incontact with a flow of water a-t 3C and a very cold
dough. An instant dry yeast rehydrated under good con-
ditions at at leas-t 30C and having been able to re-
constitute its cell membranes will give a performance
at least equal -to the control American fresh yeas-t.
The particulate frozen yeast having about 77~ of dry
matter, kept 11 weeks at -20C is incorpora-ted directly
without prior thawing.
The U.S. White Bread formula used has the
15 following composition:
U.S. flour ................. 100 parts by weight
Water ........................... 57 " "
Salt ........................... 2.25 " "
Yeas-t dry matter .......... ~...... ..1.6 " "
20 Sugar ............................... ..8 " "
Shor-tening ....................... ..5 " "
Panodan 90 (Diacetyl tartaric
ester of monoglycerides manu-
factured by GRINDSTED) .......... .Ø3 " "
2S Ascorbic acid ....................... 100 ppm
Bromate 50/50 ..... ~.............. 20 ppm (pure bromate:
10 ppm)
The temperature oE the doughs at the end of
kneading is 15C and the doughs obtained are immedi-
ately placed in a container at -~0C after moulding so
as to freeze them to -20C at the core. The duration
between -the end of the kneacling and the end of the
mou:Lding and hence the beginning of freezing is kept
constant and equal -to 25 minutes. The frozen dough
pieces obtained are kept at -20C. The dough pieces
,'~
,. i. ~
are thawed at the end of one, four, eigh-t, -twelve and
sixteen weeks in a con-tainer at ~26C where they are
brough to 4C a-t the core in 135 minutes. Then, the
proof time periods for a dough development at constant
volume, i.e. to a -template, in an incubator at 43C and
94~ rela-tive humidity, are measured.
The following results are obtained:
Proof--time expressed in minutes
1 0
Particulate Par-ticulate
Con-trol Control yeast having yeast having 7 7 %
fresh dry 77% of dry of dry matter,
US yeast yeast matter kept frozen, kept 11
11 weeks at 4C weeks at -20C
1 week 105 145 110 95
4 weeks 115 158 125 100
8 weeks 124 168 131 102
12 weeks 136 175 138 110
2016 weeks 145 182 150 118
~'here is noted on the average over several
-tests an :increase in the proof time expressed in min-
utes per week o:E preservation at -20C of the :Erozen
doughs:
Control US :E:resh yeast .............. -r2.6 m:inutes/week
Cont:ro:L dry yeast ................... -~2. 4 m:inutes/week
Frozen yeast, ~.i.nely div:Lded and
:Eree-f:Low:ing having about 77~ dry
matter, kept 11 weeks at - 20C .... -~1. 6 minute/week.
E'XAM:P:LE 3
~ frozen baker's yeast in short vermicelli of
diameter 0.5 to 1 mm, having a cIry matter content of
-J;
,1'~
abou-t 77% is prepared as in Example 1. The straln used
is NCYC No. 995 disclosed in U.S. patent No. 4,496,632.
The cultivation of -this s-train is conducted
essentially so as -to obtain a fresh yeast wi-th a rela-
tively high ni-trogen centent, equal or greater than 8%.
The emulsifier added to the fresh yeast is
sorbitan monostearate in propor-tion of 0.3% with re
spect to the dry matter of the yeast.
The analysis of the free flowing particulate
frozen yeast ob-tained is as follows (resul-ts of 8
tests):
Average
Dry matter ....................... 74 to 80 % 77 %
Nitrogen on dry ma-tter .......... 7.9 to 8.6% 8.2
15 Fermentative activity measured
in the Burrows and Harrison
fermentometer according to the
above-mentioned test Al, in 2
hours notably disclosed in -the
2Q U.S. patent 4,396,632 ..... 159 to 170 ml 162 ml of CO2
The free flowing frozen particulate yeast ob~
tained has a fermentative activity or gassing power of
the same range as that of very active fresh compressed
yeasts and a preservation at least equal -to that of
best dry yeasts, and an activity superior by the order
of 25% to that of these dry yeasts.
B~MPLE 4
A frozen baker's yeast in short vermicelli of
diameter 0.5 to 1 mm, havln~ a dry matter content of
about 77~ ls prepared as ln Exaople 1.
The straln used is an osmotolerant strain
belonging to the group of stralns NCYC R 30, NCYC 878,
NCYC 996 or NCYC 890 dlsclosed ln the U.S. patents Nos.
4,328,250, 4,318,930 and 4,396,632.
~ 13 -
These s-trains are multiplied as indicated in
the aforesaid U.S. paten-ts. The emulsifier used is
sorbitan monostearate i.n proportion of 0.3% with re-
spect to the dry matter of the yeast.
The free flowing particulate yeast obtained
having a dry matter content of about 77% has a fermen-
ta-tive activity or gassing power at least equal to 30
ml in test A4, in one hour, and preferably at least
equal to 40 ml of CO2 in test A4, in one hour, de-
scribed in the aforesaid U.S. patents.
This free flowing particulate yeast is used
for making Danish Pastry according to a formula of the
type:
Flour ............................. 100 parts by weight
15 Sugar ............................... 15 " "
Shor-tening ....................... 15 " "
US fresh yeast -~ sal-ts,
oxldants and emulsifiers ........ 15 " "
Water ............................. 50 " "
20. The kneading is performed in three steps in a
double-casing horizontal mixer containing ice-water at
-18C. The star-tiny dough temperature is of ~C and
the final dough temperature is maximum 10C.
In such a process, it is very difficult to
use dry yeast unless this yeas-t is rehydra-ted at at
least 20C and after 1 hour, the yeast cream obtained
is cooled down.
3 to 5 parts by weight of the free flowincJ
particulate yeast i.s incorporatecl directly into the
dough in place of the 15 parts by weight of fresh
comp:ressec~ yeast to obtain at least the same dough
development.
,i,
