Note: Descriptions are shown in the official language in which they were submitted.
2~1~26~
Gist-Brocades N.V.
2637-S
Ini3tant dry yeast
The present invention relates to an instant dry yeast
composition, the production thereof and its use in bakery
products and beverages.
The manufacture of yeast starts with a small sample of
5 a pure culture. This sample is used to inoculate the first
of a series of fermentations in fermentors of successively
increasing size. The first few are mildly aerated batch
fermentations. Only the last two (or sometimes three) stages
are performed using full aeration and incremental feeding of ~-
10 molasses. These fed-batch fermentations are carried out in
fermentors having a volume of 100 m3 or more. Fermentation
time is typically in the range of 12-20 hours, in which some
10,000-30,000 kg of compre~sed yeast is produced.
I Further processing includes separating the yeast from
j 15 the broth by centrifugation and washing which results in
I yeast cream (17-23% (w/w) dry matter content).
The yeast cream may be processed into compressed yeast
(27-33% (w/w) dry matter content) which is either sold as
such or extruded and dried to produce active dry yeast (ADY)
20 or instant dry yeast (IDY) with moisture contents of 6-8%
¦ (w/w) and 2-8% (w/w), respectively.
¦ In the case of ADY, drying usually takes place in belt
! or rotolouvre (drum) dryers. For IDY production fluidized-
¦ bed drying is commonly used. Drying of the yeast to a level
25 of about 20% water content involves only the evaporation of
~, free water. Further reducing of the moisture content
involves the removal of a portion of the bound water from
the yeast which may cause damage to the yeast cell membran~.
In US patent 3,843,800 and US 4,248,420 wetting agents such
30 as esters of saturated fatty acids of glycerol and/or fatty
:1 .
- 2 - 2~
acid esters of propylene glycol are added to preserve the
desired high direct leavening activity of the yeast during
the drying step.
Dry yeast loses part of its leavening activity during
5 the drying process as well as during the rehydration
procedure. Dry yeasts are still commonly used in the bakery
trade because of their extended stability and because
refrigeration is unnecessary. Dry yeasts are used in wine
making to obtain a fast and reproducible fermentation
10 thereby minimizing the risk of failure of the natural
fermentation. Moreover, the yeast is immediately available
throughout the year.
Instant dry yeast (IDY) is the latest type of baker's
yeast, introduced in the early 1970's (see for example
US patent 3,843,800) a few years later followed by instant
dry wine yeast (IWY), which can be seen as a special form of
instant dry yeast. To obtain a high quality IDY, compressed
yeast of relatively high protein content (42-60% (w/w)) must
be dried in a quick-drying process. The leavening activity
20 of IDY under conditions of application is about 75-85% that
of compressed yeast; the shelf life in a vacuum-sealed
package is comparable to that of ADY.
IDY is presented typically in the form of very small
rods that are highly porous and easy to rehydrate. On the
25 one hand, this allows immediate use, without prior
rehydration. On the other hand, the high porosity gives easy
access to water and oxygen (from air), which results in a
rather rapid loss of activity upon exposure to atmospheric
conditions. For satisfactory results, IDY should be used
30 within 3-5 days of opening the package. ~oreover, the high
porosity of IDY makes it sansitive to extreme rehydration
conditions.
IDY usually has a moisture content of 2-8% (w/w) and a
protein content between 42 and 60% (w/w) on a dry matter
35 basis.
~ 3 ~ 211~
As with ADY, some manufacturers add antioxidants (e.y~
BHA) to their product for improved stability. Ascorbic acid
may be added to IDY products to improve stability.
A problem encountered with ADY and IDY is the leakage
s of yeast solids from the cells upon rehydration. This
results in a loss of gassing power or a loss of capacity to
produce ethanol. The various methods of adding yeast and
mixing dough differ from country to country. Although for
the more porous IDY the dry yeast shoud be mixed with flour
before water is added, it often happens that the dry yeast
is suspended in water together with other soluble additions
before flour is added. Additives such as sugar, ~ -
calciumpropionate and salt affect yeast performance, as does
the water temperature. In countries with warm climates or
15 where bakers use high speed mixers with extra heat input,
the water is cooled, for example by adding ice, to obtain
proper dough temperatures after mixing. Under these
conditions instant dry yeast comes in direct contact with
the chilled water, thus redu~ing the yeast performance
20 substantially. In US-A-4,764,472 this problem is partly
solved by the incorporation of 0.1 to 2% by weight of locust
bean gum, gum ghatti and mixtures thereof, which prevents a
loss of activity when water of about 20C is added. However,
in practice, water of 15C or less, even sometimes a
25 water/ice mixture, is used and at such temperatures activity
after rehydration is extremely low.
We have now surprisingly found that when 1.1 to 5%
(w/w, dry weight) of a rehydration controlling agent is
incorporated in the dry yeast, the yeast is much better
30 protected against the loss of activity due to rehydration of
the dry yeast at low temperatures. The present invention
therefore provides a dry yeast composition having a moisture
content of less than 8% (w/w), preferably 3 to 6% (w/w) and
which comprises 1.1 to 5% (w/w) of a rehydration controlling
35 agent. The rehydration controlling agent has preferably a
moisture content of less than 10%. When added these agents
;.
.
.. .... . . ., . .. . -. ... .. - ~ . . -
~ 4 ~ 21~2~ '
are often suspended in water to improve the distribution in
the yeast.
The rehydration controlling agent is responsible for a
controlled rehydration (wetting) of IDY particles and the
5 individual yeast cells. This rehydration contxolling agent
functions as an extra barrier for water penetration into the
cells.
Preferably 1.5 to 3~ by weight and more preferably 2
to 3% by weight of a rehydration controlling agent is used.
10 Preferably the rehydration agent comprises at least 50~
(w/w) of an emulsifier, for example 55%, 60~, 65%, 70% or
75% (w/w).
Typical examples of rehydration contrslling agents
are:
- esters of fatty acids such as fatty acid esters of
sorbitan, e.g. sorbitan monolaurate, monopalmitate,
monostearate or mono-oleate;
- acid esters of mono and/or diglyceride such as
citric acid ester or diacetyltartaric acid ester;
- fatty acid esters of glycerol or polyglycerol, e.g.
glyceryl monostearate, glyceryl distearate or glyceryl
monopalmitate,
- fatty acid esters of propylene glycol e.g. propylene
glycol monostearate;
- arabic gum;
- xanthan gum;
- yeast extract;
~ CMC (sodium carboxy methyl cellulose)
- or mixtures of two or more of the above mentioned
30 compounds.
We have found that the addition of the rehydration
controlling agents according to the invention substantially
protects the dry yeast against a loss of activity when water
of 15C, even 10C or less is added to the yeast.
The rehydration controlling agent is added before the
final drying step when the yeast is still wet. The yeast is
thus protected during this drying step, there~y preserving
~ 5 ~ 21 ~2~i~
the desired high leavening activity of the yeast. When the
yeast is mixed in the flour, gassing power under standard
conditions is unaffected.
Surprisingly, when the yeast was rehydrated in water,
5 the performance of the instant yeast improves substantially~
The greatest improvement is attained at the lowest
temperature.
The present invention further provides a method for
preparing a dry yeast composition which comprises drying
10 yeast in the presence of 1.1 to 5% (w/w) of a rehydration
controlling agent. The present invention additionally
provides a method of preparing bread which comprises
incorporating into a dough a composition as claimed in any
one of claims 1 to 7 and baking the dough.
It will be appreciated that the dough will contain
besides the yeast, ingredients generally used in dough
preparation.
Surprisingly it has been found that in a dough
prepared with the yeast of the present invention the rate of
20 the gas production is increased and the bread volume of the
baked product increased substantially.
The amount of rehydration controlling agent present in
the yeast may be varied according to different application
methods.
All publications and patent applications cited in this
specification are herein incorporated by reference as if
each individual publication or patent application was
specifically and individually indicated to be incorparated.
30 Performance of the yeasts prepared according to the present
invention.
a. This test was carried out under optimal instant
3S yeast conditions.
300 mg of instant dry yeast was mixed with 62.5 g o~
flour. After addition of 34.4 ml of a solution containing
1.25 g of NaCl, the mass is mixed for 6 minutes at 28 a C into ;
- 6 2~14~
a dough and placed in a water bath at 28C. The voluma of
gas produced within the period from 10 to 175 minutes after
the start of mixing was determined in ml at 28C and
760 mm Hg.
bl. Identical to (a) except the yeast was wetted as
a monolayer of particles on a water surface by means of a
small funnel in an erlenmeyer-flask at 35C, thus allowing
every particle to come directly into contact with water. The
test was therefore carried out under maximum rehydration
10 conditions.
b2. Identical to (bl) with water temperature of
20C.
b3. Identical to (bl) with water temperature of
10 ~C.
Example 1
Experiment 1:
The tests (Examples 1 to 5) were carried out using
fresh baker's yeast, a normal cultivation of strain 210 Ng,
20 CBS 406.87. This product has a moisture content of
approximately 68% and a protein content of approximately 50%
on dry weight. This block yeast was compresssed to reduce
extracellular moisture content to 66%. ~ `
This yeast was crumbled and mixed with 0.25% of the
25 rehydration controlling agent Span-60TM (sorbitan
monostearate) (on basis of total dry weight) using the
following procedure:
The Span-60TM was melted at 65~C and suspended in
water at 60C using a high sheer laboratory mixer. This
30 emulsion was added to compressed baker's yeast up to a
content of 0.25~ on total dry weight.
The combination was then extruded three times
through a screen with holes of 0.8 mm to form rod-shaped
j particles, containing the rehydration controlling agent
35 properly distributed.
,,;,` , " , ` . : . ; ~ ~ ~ ,
_ 7 _ 2 ~ ~2~
The product from this exercise was pressed ~inally
through a screen with holes of 0.8 mm to form again rod-
shaped particles.
The drying of this product was performed in a
s laboratory scale fluid bed-dryerl consisting of a conical
glass tube built on an air 5Upply system, fenced by an
appropriate screen to create a calm fluidisation pattern.
The air supply system consisted of a two way control valve/
leading air partly through an electrical heaking section. By
10 means of this control valve a constant outlet air
temperature of 39C was maintained during the drying. The
airflow was set at a superficial speed of 1.6 m/s at the
bottom of the conus.
The airflow was stopped as soon as the inlet-air
15 temperature had reached a temperature of 45C.
The product was collected and packed in sachets
under vacuum for analysing.
ExT~eriment 2
As described in test 1, but with the Span-60
constituting 0.50% of the total dry matter.
Experiment 3
As described in test 1, but with the Span-60TM
25 constituting 0.75% of the total dry matter.
Experiment 4
As described in test 1, but with the Span-60TU
constituting 1.0% of the total dry matter.
Experiment 5
As described in test 1, but with the Span-60TM
constituting 1.50% of the total dry matter.
35 Experiment 6
As described in test 1, but with the Span-~OTM
constituting 2.0% of the total dry matter.
8 - 2~ 1~2
Experiment 7
As described in test 1, but with the Span-60
constituting 3.0% of the total dry matter.
Results in gassing power of ~xam]ple 1:
, ~ _ , .
AdditionResult Resu:Lt Result Result
test a test bl test b2 test b3
(ml) (ml) (ml) (ml)
¦Span-60T~ 0.25% 283 173 83 29
¦Span-60TM 0.5%290 207 130 69 ¦
10 ¦Span-60TU 0.75% 290 223 159 85
¦Span-60T~ 1.0%300 227 170 88
i I
¦Span-60TU 1.5%304 246 197 122 ¦
¦Span-60TU 2.0%303 249 189 123 ¦
¦Span-60T~ 3.0%298 248 201 129
~xample 2
The experiment was carried out in a manner identical
to Example 1, but with a commercially available citric acid ~ -
20 ester o~ glycerine monostearate (CGM) as rehydration
controlling agent.
Results in gassing pow~r of Example 2:
Addition Result Result Result ¦ Result ll
test a test bl test b2 ¦ test b3 ¦¦
(ml) (ml)(ml) ¦ (ml)
l ,
25 ¦ CGM 0.25%288 174 96 ¦ 37
CGM 0.5% 290 193 128 ¦ 54
CGM 0.75% 297 215 146 ¦ 71
CGM 1.0% 300 225 165 ¦ 93
~ CGM 1.5% 303 241 181 1 98
i l 11
30 I CGM 2.0% 307 233 189 ¦ 109
l CGM 3.0% 310 249 199 ¦ 121
9 21~2~
~xample 3
Identical to experiment 1 of Example 1 except for the
concentration of rehydration controlling agent being Span-
5 60TU at a final concentration of 1.0% and an extra additionof yeast extract powder to a final concentration of 2.0%.
Example ~
Identical to experiment 1 of Example 1 except for the
concentration of rehydration controlling agent being Span-
60~M at a final concentration of 1.0% and xanthane gum
solution to a final concentration of 1.4%. ~ -
15 Example 5
Identical to experiment 1 of Example 1 except for the
concentration of rehydration controlling agent being Span-
60TU at a final concentration of 1.0% and sodium carboxy :~ :
20 methyl cellulose to a final concentration of 1.0%.
Results in gassing power of Example 3 to 5. ~ ~-
Addition Result Result Result Result
test a test bl test b2 test b3 l
(ml) (ml) (ml) (ml) .
l Span-60TM 1.0% + low 298 244 229 133
25 1 salt yeast extract I .
2.0% (d.m.) ::
Span-60TM 1.0% + 308 282 246 157
xanthane gum 1.4%
(d.m.) .
30 l Span-60TM 1.0% + sodium 299 261 213 151
carboxy methyl
cellulose 1.0% (d.m.)
-lo- 211~
E~ample 6
Identical to experiment 4 of Example 1 except for the
strain applied being 227 Ng, CBS 155.91 (deposited on March
5~ 1991)-
Example 7
Identical to Example 6, except for the choice andconcentration of rehydration controlling agent being CGM at
a final concentration of 2.5%.
Example 8
Identical to Example 6, except for the choice of
rehydration controlling agent being a combination of 1.0%
Span-60TU and 1.0% sodium carboxy methyl cellulose dissolved
as a 5% solution in water before mixing with the Span-60
emulsion.
Results Example 6, 7, and 8
_ __
Addition Result Result
test a test b3
(ml) (ml)
span-60TM 1.0% 325 87
CGM 2.5% 324159 ¦
Span-60TM 1.0% + sodium 319 146
carboxy methyl cellulose
1.0% (d.m.)
E~ample 9
Identical to experiment 4 of Example 1, except for the
strain applied being 237 Ng, CBS 158.86 (deposited on March
25, 1986) a sugar resistant type of strain.
~o
Contrary to Examples 1 to 8 the gas performance tests
with the samples of Example 9, 10 and 11 were carried out
applying an extra addition of 10% sugar on flour weight.
2 ~ 2 ~
Examplo 10
Identical to Example 9, except for the choice and
concentration of rehydration controlling agent being CGM at
a final concentration of 2.5%. .
~xampl~
Identical to Example 9, except for the choice of
rehydration controlling agent being a combination of
Span-60T~ and sodium carboxy methyl cellulose as in
10 Example 8.
Results Example 9, 10 and 11
Addition Result Result
test a test b3
(ml) (ml) l
Span-60TM 1.0% 270 59 ~:
CGM 2.5~ Z68 89
Span-60TM 1.0% + sodium271 92
carboxy methyl cellulose ¦ :
¦1.0% (d.m.)
E~ample 12
In one type of baking trial producing French batard
type of bread (method I) 3000 g wheat flour having a
temperature of 20C, 1.75% salt, 1% Unipan Plus~ ~bread
25 improver, Gist-brocades), and 0.45~ instant dry yeast of
227 Ng strain (CBS 155.91), containing varying contents of
rehydration controlling agent being CGM, are mixed by hand
in the bowl of a Phebus mixer. Afterwards 56% water having a
temperature of 32C is added and kneading starts (2 minutes
. 30 at speed 1 and 18 minutes at speed 2). The dough temperature
~ is 27C. The dough is given a first proof of 15 minutes in a
i proofing cabinet at 30C and 85% RH. Afterwards the dough is
I divided into 12 pieces of 350 gO These pieces are moulded
J and given an i.ntermediate proof of 15 minutes at 30C and
35 85~ R5. A~ter this stage the pieces sre again moulded,
- 12 - 21~2'~
shaped, and givan a final proof of 110 minutes at 30C and
85% RH. Afterwards the fully proofed doughs are brought into
the oven and baked at 240C for 25 minutes.
In a second type of baking trial producing French
5 batard type of bread (method II)y 3000 g wheat flour having
a temperature of 42C, 1.75% sal1:, 1% Unipan Plus~ (bread
improver, Gist-brocades) are introduced in the bowl of the
Phebus mixer. 0.45% Instant dry yeast of 227 Ng strain,
containing varying contents of rehydration controlling agent
10 being CGM, is spread over the surface of this mixture.
Afterwards 56% water having a temperature of 4C is poured
out over the surface and mixing starts with 2 minutes at
speed 1 and 28 minutes at speed 2 to reach the dough
temperature of 27%. Dough handling, fermentation and baking
15 procedure is the same as described above, only the final
proof time is varying. Final proof time is determined by
putting 45 g of dough (after first and second proof) in a
standardized measuring cylinder and let it rise to a fixed
height of 10 cm.
In both methods, after cooling down to room
temperature, loaf volumes are obtained by the rapeseed
displacement method. Results are shown in the Table
hereinbelow. Loaf volumes are an average of volume
measurements of 4 loaves of bread.
From this Table it is clear that in method I, using
flour of 20~C and water of 32C, an increase in loaf volume
is seen after introducing instant yeast containing a higher
rehydration controlling agent.
This result corresponds to the gassing results shown
30 in Example 2.
Breadmaking according to method II leads to shorter
final proof times and somewhat higher loaf volumes in those
cases where instant yeast is used having a higher
¦ rehydration controlling agent.
.
2 g ~ :
Loaf volumes of Example 12
, . .
Method I Method II
addition Loaf volume Final proof Loaf volume
l (ml) time (min.) (ml)
C&M 1.0% 1460 160 1336 :
CGM 1.5% 1472 150 1393 ~::
CGM 2.0% 1514 _ 135 1419
~GM 3.0% 1563 135 1377 :~ :
As a consequence of the shorter final proof times the
overall bread quality is improved: a better break and shred
of the crust and a fin~r texture of the crumb.
