Method for producing cheese by means of microfiltration

The object of the present invention is the treatment of a curd (5) obtained from milk (1) which had been subjected to a pretreatment aimed at coagulating the milk casein and precipitating the whey protein through a microfiltration loop (30) comprising at least one cartridge (34) with ceramic tubes (36), so as to separate the cheese from the whey. The device comprises a means for a sequential unclogging under high pressure (39, 43, 44) by reverse permeation for a short period of time without interrupting the continuous microfiltration. Advantages: increased useful life, no clogging, cleaning and sterilization with all the acid and alkaline products used in a dairy plant, insensitiveness to pH, preservation of the quality of the product, low pressure drop across the membrane, high yield.

The object of the present invention is the production of a cheese from milk 
which is subjected to a special filtration. 
The production of a cheese is carried out through a number of essential 
steps well known in the cheese industry. The first step consists in 
treating the milk to obtain a lactic curd. In the following description 
and in the claims, one should understand by "milk" all milks of animal or 
vegetable origin with or without previous pretreatment. Hereinafter "milk" 
may also be referred to as "raw milk" which includes homogenized and 
precipitated milks and/or milks wherein the curd has been precipitated 
from the whey and other water soluble constituents/materials of the milk. 
The curd obtained is then subjected to a separation step called draining 
aimed at separating the precipitated asides which form a coagulum 
entrapping both the globules of fat and the whey proteins which had 
precipitated, the mixture being called "cheese", from constituent water 
with unprecipitated soluble products, in particular products containing 
soluble nitrogen, lactose, inorganic salts, this mixture being called 
"whey". This step, which consists in a separation by gravity within the 
product divided into units of a small volume, is long and expensive and 
cannot be compatible with the present day food processing industry. 
Improvement of this type of production was sought through the use of 
centrifuges of standard but limited performance. 
French Patent No. 2 232 999 proposes an ultra filtration process on an 
organic semipermeable membrane enabling the recovery of the totality of 
the proteins by passing a standard coagulum through this organic membrane. 
Such a process has numerous drawbacks, starting with the organic membranes 
themselves, as used for carrying the process into effect, because they 
remain sensitive to physical parameters such as the pressure and the 
temperature during the course of the process, and also to chemical 
parameters such as the pH of certain strong acids or alkalis used when 
cleaning and/or sterilizing. Further, ultrafiltration is a technique which 
has limitations with regard to a product such as curd, because the organic 
membranes have an opening or pore diameter which ensures the retention of 
the totality of the proteins, therefore of the unprecipitated proteins, 
thus leading to a rapid clogging of the filters, which phenomenon is 
amplified by the polarization at the level of the organic membrane itself. 
Further, it is impossible to proceed to the unclogging during the 
continuous operation of ultrafiltration. Therefore, these periodical 
uncloggings imply stopping the installation and a full cleaning cycle. 
The object of the present invention is to propose a manufacturing process 
for a cheese and an associated device for carrying the process into 
effect, the main characteristic of which is that the milk is subjected to 
a step where the proteins precipitate and the casein coagulates for 
obtaining a curd, the curd being thereafter subjected to at least one 
continuous mechanical separation by microfiltration through ceramic walls, 
this microfiltration step comprising sequential uncloggings without 
interruption of the microfiltration so as to maintain a very low pressure 
drop across the membrane. 
The sequential unclogging of the process is carried out by reverse 
permeation under high pressure in a very short time. 
Also, in order to limit the pressure drop across the membrane, the permeate 
outlet is restricted so as to create a back pressure. 
This process is further characterized in that the curd is subjected to a 
thermal treatment prior to the microfiltration, so as to obtain an 
additional precipitation of the whey proteins. 
The process according to the invention is carried out by circulating the 
product under conditions of laminar flow through the ceramic tubes of the 
microfiltration cartridge. According to this continuous process, a speed 
in the range from 1 to 10 meters per second and, preferably from 3 to 5 
meters per second, is provided. The microfiltration is carried out 
stepwise, so as to take also into account the increase in viscosity. 
The process is carried out under controlled constant pressure and 
temperature, which implies the provision of cooling zones for the purpose 
of taking into account the temperature increase of the product during its 
circulation. 
The device enabling to carry into effect the process is comprised of at 
least one microfiltration loop comprising a ceramic cartridge fed with the 
product by a circulating means, a first permeate outlet connected to a 
storage tank, a branch circuit for a portion of the permeate towards a 
storage tank under high pressure, a second permeate outlet connected to 
said storage tank under high pressure, an outlet for the filtration 
residue. This microfiltration loop is series mounted on the main feed 
line. 
The device further comprises a shut-off valve on the first permeate outlet, 
and a means for restricting the flow upstream of the branch circuit, a 
shut-off valve between the second permeate outlet and the storage tank 
under high pressure. A means for controlling the circulating flow is 
placed upstream of the downstream flow restricting system and downstream 
of the upstream shut-off valve. The device is further provided with a 
pressure control means in the loop, this pressure control means being 
capable of acting on the restricting means. 
The storage tank under high pressure is fed with the permeate through the 
branch circuit on which is disposed a high pressure pump. 
The storage tank is of the two-fluid type, one of which is compressible, 
for example nitrogen. 
The storage tank can also be of the single-fluid type connected to a high 
pressure source with a relief valve, this high pressure source being if 
desired, an auxiliary nitrogen container. 
The device according to the invention comprises several microfiltration 
loops branching from a main line. 
This device is unclogged sequentially by reverse permeation under high 
pressure by opening the shut-off valve disposed on the second permeate 
outlet loop by loop with preliminary sequential isolation by closing the 
shut-off valve disposed upstream of the restricting means. 
The tubes in the ultrafiltration cartridges mounted as a bank are made of 
ceramic of the .alpha. aluminum type with an average pore diameter in the 
range from 0.2 .mu.m to 5 .mu.m. 
Such a process offers the advantage of remaining applicable to numerous 
types of productions, because the permeate flow, the residence time in the 
device, the qualities of the end product can be controlled very 
accurately. The end product exhibits a fine regular homogeneous structure, 
due to the low pressure drop across the membrane and to the fact that the 
flow is laminar and does not affect the molecules themselves. 
The process can operate without interruption and the useful life of the 
device is increased by the use of a ceramic. The device can be cleaned 
with a 2% sodium hydroxide and a nitric acid solution, thus obviating the 
need for using specific products for each type of membrane as it is the 
case when using organic membranes. Further, the reverse permeation under 
high pressure causes a negligible dilution of the filtration residue 
because the duration of the permeation is extremely short, which improves 
the yield of the installation. This process using this type of unclogging 
requires only very little room because the flow per unit of surface is 
high, which is primarily due to the highly hydrophobic character of the 
ceramic and to the high porosity of the membranes. 
Now, we shall proceed to the description of the process and of the device 
by means of a particular embodiment of the invention not intended to limit 
the scope thereof, wherein reference is made to FIGS. 1 and 2 which show: 
FIG. 1: a block diagram of the process according to the invention, 
FIG. 2: i a detailed view of the microfiltration device of the invention.

The process according to the invention uses milk 1 which is homogenized in 
a homogenizer device 2 under double pressure and decompression. Such a 
homogenizer prevents the fat from rising and the occurrence of two phases. 
The pasteurization of step 3 is carried out continuously by rising the 
temperature to within the range from 85.degree. to 95.degree. C. during 2 
to 5 minutes. The effect of this pasteurization is to precipitate the whey 
proteins which are normally solubilized. The pasteurized milk is cooled at 
4 to a temperature within the range from 20.degree. to 45.degree. C., and, 
more particularly, from 24 to 28.degree. C., this temperature 
corresponding to the coagulation temperature. 
Adjuvants are added to promote the coagulation of the milk caseins. Rennin 
and/or lactic ferments can be used in a known manner, but also chemical 
flocculation, in particular, through the use of acidification. The product 
obtained called lactic curd has a strongly acidic pH, beneath 4.6. 
The coagulum obtained after the necessary reaction time, which depends on 
the type of curd desired, is subjected to a de-curding step through mixing 
5 which yields a homogeneous thick "paste", this homogeneity being 
perfected by a pumping 6 using a centrifugal pump. 
This thick paste can be treated directly by microfiltration 8 or be 
subjected to an additional thermal treatment 7 for the purpose of 
improving the precipitation of the whey proteins, because these 
solubilized proteins would not be retained during the microfiltration. 
This thermal treatment consists in heating to a temperature in the range 
from 55.degree. to 85.degree. C. for a period of time which can vary from 
0 to 5 minutes. The curd is cooled immediately thereafter, and the product 
obtained has a firmer consistency and a stronger hydrophobic character. 
The microfiltration 8 separates the cheese from the whey, the device being 
detailed hereafter with reference to FIG. 2. The cheese then contains the 
totality of the fat and the major part of the protein nitrogenous matter, 
as well as a proportion of the soluble substances which remain bound to 
the proteins and also a certain amount of water. 
The whey or permeate contains no fat but contains a small percentage of 
soluble proteinic nitrogeneous matter which had not precipitated (1 g/l), 
lactose, inorganic salts, and water. 
The whey or permeate is thereafter transferred to be used in a well known 
manner, as a by-product. 
As to the cheese, various subsequent treatments 9 are applied in view of 
its consumption and they depend on the type of product which needs to be 
produced. Such subsequent treatments include aromatization, addition of 
various elements such as salt, sugar, spices, figurative elements, etc . . 
. , homogenization, smoothing, thermal treatment, ripening and finally, 
packaging. 
The microfiltration device of FIG. 2 comprises a main circuit 19 fed with 
the mixed curd obtained in step 5 of the process and pumped in step 6 of 
the same process. The feed pump 60 is followed by a series of temperature 
21, pressure 22, and flow rate 23 sensors. On this main circuit, there is 
series mounted a first microfiltration loop 30. A valve 31 prevents any 
return of the product to the main line. A recirculation pump 20 sucks the 
raw mixed curd and delivers it to a microfiltration means after control of 
the pressure 32, the temperature 33. 
The microfiltration means consists of at least one cartridge 34 comprising 
a metal jacket 35, generally made of stainless steel so as to withstand 
the various mechanical and chemical aggressions, inside which jacket there 
is disposed a bank of ceramic--alumine .alpha. of a controlled 
porosity--tubes 36, the ends of which are bound to plates 37 so that the 
product flows in the tubes and the permeation occurs from the inside of 
the tube outside. Such cartridges are commercially available under the 
trade name MEMBRALOX. The metal jacket is connected at both ends to the 
recirculation circuit, but two permeate outlets 38, 39 having shut-off 
valves 40, 1 are also provided. The first outlet 38 is connected to the 
permeate collector 42 and the second outlet 39 is connected to a storage 
tank 43 of the accumulator type, i. e. having a portion of its volume 
filled with a compressible fluid 44. 
A restricting means in the form of a progressive valve 46 is disposed on 
the permeate collector so as to create, when it is closed, a back pressure 
in the permeate circuit connected to the first outlet. 
Upstream of this restricting means, a flowmeter 45 completes the permeate 
evacuation line. A branch circuit 7 provided with a nonreturn valve 48 
feeds the high pressure pump 49 which in turn feeds the permeate storage 
tank maintained under pressure by the compressible fluid. 
The filtration residue flowing out from the cartridge 34 is directed to the 
recirculation pump upstream of which there is provided a branch circuit 
with a nonreturn valve 50 connected to the main circuit and the outflow of 
which corresponds to the inflow arriving to the loop less the flow of 
permeate. One passage can be continued in the same manner through several 
successive loops 51, 52 comprised of the same components as loop 30 
described in detail immediately above. 
This microfiltration device is provided with all the auxiliary equipment 
well-known in the construction of systems, such as isolation valves for 
allowing maintenance, collars, flanges, joints and other reducers, this 
equipment not coming within the scope of the invention, nor does the 
control of the installation by means of a computer or of a programmable 
automation. 
However, the example which has just been described is only an exemplary 
embodiment capable of variations by means known to those skilled in the 
art, which are, accordingly, considered as included in the present 
invention. For example, in order to keep the temperature of the product 
constant while heating occurs through circulation, a cooling device can be 
provided on each microfiltration loop. 
Also, the unclogging sequences, the pressure in the storage tank, the 
opening time of the valves controlling the counter-current inflow of 
permeate under high pressure or the restriction on the permeate line are 
selected according to the product. The same holds true when it comes to 
finding the best compromise possible between the highest temperature which 
does not affect adversely the product and the minimal temperature yielding 
this same product with the lowest viscosity possible. 
An example of a product obtained according to the process using the 
specific device which has just been described can now be given. 1000 grams 
of milk having the following composition 
______________________________________ 
Grams 
______________________________________ 
Fat 63.35 
Nitrogenous proteinic matter 
29.40 
De-fatted dry matter 
53.03 
Water 854.23 
yielded: 
300 grams of cheese 
Dry matter 103.50 g, of which 
Fat 63.00 g 
Nitrogeneous matter 28.40 g 
Water 196.50 g 
700 grams of whey 
Dry matter 42.00 g, of which 
Nitrogeneous matter 2.10 g 
Water 658.00 g 
______________________________________ 
The present invention is not limited by the exemplary embodiments described 
hereabove, but is on the contrary, capable of modifications and variations 
which will become apparent to those skilled in the art.