Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION:
The present invention relates to a process for the separation of
whey from high solids curd in the manufacture of cheese, and in
particular to the addition of water to the formed-curd for that purpose.
R~GROUND OF THE INVENTION:
Most conventional types of cheese are fermented products produced
through the combination of: the curdling action of a proteolytic enzyme
(typically rennet - an enzyme complex found in the stomach of young
mammalian An;r~ls); and, 2) the pH reduction that is facilitated by the
acidic metabolites of "lactic" microorganisms. The resulting product is
a curd whose major protein constituent is casein, the predominant
protein species in mammalian milk. Additionally cheese typically
contains some of the minerals and most of the fat that are originally
contained in the milk at the outset of the cheese-making process. The
balance of the milk components becomes a liquid phase by-product
following precipitation of the curd. This liquid phase is known in the
art as "whey", and contains the other major protein species of milk -
whey protein. In any case, whey characteristically contains not only
the indigenous milk proteins and minerals that are preferentially
soluble at the relatively acid pH that typically manifests under
conventional cheese-making process conditions, but also most of the
lactose contained in the milk.
Curdling almost invariably includes souring of the milk, usually
through in-situ acid production by S. lactis, and/or other lactobacilli,
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although addition of exogenous acids, (typically food grade organic
acids), is not unheard of. In some cheese manufacturing the curdling is
entirely a function of acid souring of the milk, with no rennet or other
enzyme involvement.
In still other cases, various microbial proteases are substituted
for the more traditional rennet.
After the curdling operation is sufficiently advanced (and in fact
nearing completion), the coagulate must be separated from the whey, in
order to produce a structurally robust, substantively dewatered curd,
having a firm, and almost rubbery character. The realization of this
end typically requires the cutting of the curd with curd knives to
facilitate the "bleeding" of the whey from the body of the formed curd.
The cut curd is periodically, and usually relatively gently, stirred to
help prevent the curd cuttings from sticking to on another, or settling
and "matting", either of which would otherwise interfere undesirably
with the syneretic loss of whey from along the cut surfaces of the curd.
In high solids curd processing, there is an attendant increase in
the innate tendency towards liquid retention within the high-solids
coagulum network which frustrates the downstream dewatering that is so
necessary in order to arrive at the desired cheese's final, finished
texture. Moreover, stirring becomes more difficult, as the tendency of
the curd to matt is greater than in lower solids cheese cruds.
The problem of forming a firm, self-supporting cheese, while at the
same time dealing with the complications inherent in the problem of
subsequently dewatering a high-solids coagulum, have given rise to
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significant commercial difficulties in high solids processes for cheese-
making. This continues to be the case in spite of the clear and long
standing desirability to utilize high solids levels in a cheese making
process.
One solution to this problem has been offered through the use of
machines such as that described in US 4,756,243, dated July 12, 1988,
which is adapted for extracting whey from high solids cheese. This is
a capital intensive solution that is not necessarily justified by the
increased plant throughput associated with a high-solids curd process.
Accordingly, there r~ nx a need in the art for a process which
might facilitate the de-watering of high solids curds in producing
cheese products.
SU~aRY OF THE INVENTION:
In an exemplary embodiment, the present invention relates in part
to a process for setting up the curd coagulum in a buttermilk cheese
product. Buttermilk is a by-product of butter manufacturing. Milk is
churned to produce a mechanical inversion of the fat-in-water emulsion
which is characteristic of milk, into a water-in-fat emulsion. As the
working of the inverted emulsion progresses still further, more and more
of the liquid fractions of the milk are occluded from the water-in-fat
emulsion, until finally, butter is formed. Butter typically comprises
about 80% butterfat, 1 to 2% and preferably 1.3 to 1.5 % non-fat milk
solids, and 0 to 2 % salt. An exemplary butter product might comprise
about 15.8 to 17.2% moisture; 79.5 to 80.5% butterfat; 1.7 to 2.0% salt;
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and, 1.3 to 1.7% milk-solids-not-fat. Buttermilk on the other hand is
made up of the residual milk components that are left behind after the
butter is formed. Buttermilk typically comprises 24 to 33% total solids
and 1.5 to 2% butterfat.
The present process entails concentrating the buttermilk to produce
a high solids content cheese. Of course, concentrating milk in
conventional (ie. those not including buttermilk) cheese making
processes is also known, and typically the purpose of doing so in this
more conventional cheese making context has to do with either:
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-improving the volumetric throughput of a given
sized production facility; or,
-reducing the amount of whey protein losses from
the cheese product,
through the manufacture of high-solids curds.
In the buttermilk application, of course, the concentration of the
buttermilk solids serves to overcome some of the reluctance of the
buttermilk to coagulate, by providing a certain amount of body during
gel formation.
Whether buttermilk is employed or not, however, the processing
objective in accordance with the present invention still has to do with
realization of high-solids curd formation.
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In accordance with the present invention, there is provided a
process for facilitating the stirring of cut high-solids, cheese curd.
As explained earlier herein, once a high-solids cheese curd is formed,
the cutting of the curd to release the entrained whey is complicated by
the fact that the cut-surfaces of adjacent portions of curd tend to re-
form or anneal, making stirring difficult. Moreover, expressed liquid
in normaly wheying-off facilitates heat transfer that further encourages
release of the whey from the cut curd. In tha absence of such liquid in
high solids cut curd, the release of whey is retarded.
In accordance with this aspect of the present invention, therefore,
there is provided a process for the cutting of a high-solids curd
comprising the steps of adding water, which may also be at an elevated
temperature, to the curd after it has reached the desired consistency
and either before or following cutting, and then stirring same in the
presence of the heated water. The presence of the heated water
lubricates the surfaces of the cut curd, thereby facilitating the
"stirring", and ultimately the syneretic expression of whey from the
curd.
Accordingly, it is the addition of heated water (including by way
of the addition of whey permeate or whey itself) to a formed high-solids
curd that thereby facilitates the necessary stirring (without breaking
down the curd structure) for the efficient dewatering of that coagulated
curd, (ie the removal of water therefrom).
In general, the use of the high solids milk is known to be
desirable because of the improvement in overall plant through-put that
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can be realized. High solids milk herein includes any starting milk
that has been condensed, ultrafiltered, or subjected to reverse osmosis,
or otherwise similarly treated to increase the solids content over that
typically associated with the native milk.
DET~TTFn DESCRIPTION OF THE INVENTION:
INTRODUCTION TO THE DRAWINGS:
Over the course of the following detailed description of the
present invention, reference will be made to the accompanying
drawings, in which:
Figure 1 is a flow chart outlining in a schematic form,
the process steps according to the present invention;
and,
Figures 2 is a graphical representations of stylized
water loss profiles for a conventional curd, and for a
high solids buttermilk curd, both in accordance with the
preferred practice of the present invention and, without
the benefit of added water(liquid), respectively.
In accordance with one aspect of the present invention there is
provided a process for which raw milk 1, having an acceptable odour,
being antibiotic free and stored at a temperature of four to seven oC,
is sourced. The raw milk 1 is heated to about 49 oC during the
separation of the skim milk. The skim milk is then evaporated in an
evaporator 2, under low heat conditions, of about 72 oC with a 15 second
holding time. The total solids content reaches about 18%.
Similarly, raw buttermilk 3 having a pH of greater than 6.8, being
antibiotic free and stored at a temperature of less than 42 oC, is
obtained. The buttermilk 3 is then passed to an evaporator 4 and after
being subjected to low heat of about 72 oC from a period of about 15
seconds, the total solids content of the buttermilk should be about 18%,
(eg about 6 - 7% coagulable protein). When alternative heat processing
conditions are employed, heat exchanger 5, can be optionally used, to
cool the buttermilk as required. In any case, the condensed buttermilk
is acidified through the addition of lactic acid to a pH of about 6Ø
The acidified condensed buttermilk is then preferably, but not
essentially, held for a period of about 2 hours, preferably under a
relatively high rate of agitation in a blender 6.
The acidified, condensed and aged buttermilk is then blended with
the condensed skim milk, in a ratio of 2 parts buttermilk to one part
skim milk. The blend is then optionally heated in a heat exchanger 7,
to about 95 oC and CaCl2 is added at the rate of from 2 to about 10
ounces per 1000 pounds of the blend.
Alternatively, the condensed buttermilk and milk can be mixed, and
then acidification can be carried out through the addition of the food
grade acid.
The blend is then inoculated with a thermophilic starter culture,
such as Lactobacillus bulgaricus, for example, and the rennet complex is
added to the blend.
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The coagulation process continues in the cheese vat 8, until the
desired degree of consistency is realized. Typically, the pH of the
product at this point will be about 6Ø The set cheese is then cut.
Cooking of the cut cheese with added water follows, by heating the
cheese to about 52 oC for a period of about 60 to 90 minutes. The
predraw elicits about 45% of the whey, typically at a pH of about 5.9.
The draw curd on the table 9 typically has a pH of about 5.8.
Refer in this connection to Figures 2. Figure 2 illustrates the
dynamics of whey loss from conventional cheese curds, following cutting.
The rate of loss moves quickly higher following the cutting of the curd.
However, as is also shown in Figure 2, buttermilk curd tends to retain
the whey, and the removal of whey can be difficult and protracted
process.
The cheese is then salted to taste. Note that the elapsed time
from the onset of rennet addition, to the addition of the salt, should
be on the order of four hours. The cheese is then packaged into pre-
lined drums 10, and pressed for 45 to 60 minutes. The cheese should
then be stored at temperatures of less than 4.5 oC.
