EP0179843A1 - Method for producing curd from concentrated milk - Google Patents

Abstract

The milk is concentrated so that the non-fat solids content exceeds 16%. The concentrate is renneted and allowed to coagulate, after which the cheese curd thus obtained is cut again before the coagulated body has a firmness corresponding to 300 g according to a measurement carried out on a Stevens texturemeter at 38oC. The cut cheese curds are immediately transferred to cheese molds and then processed in the usual way.

Description

Method for producing curd from concentrated milk

The present invention relates to production of curd from concentrated milk, which milk is renneted, is brought to coagulate, is cut, is filled into moulds and aftertreated in usual manner.

It is known earlier to produce cheese from concentrated milk by two fundamentally different methods.

One of the methods comprises the steps pre-treatment, concentration by way of ultrafiltration, coagulation, cutting, if necessary separation of whey, filling in the cheese moulds and after- treatment. This method is for example described in SE 427 407 and is suitable for production of cheeses with a granular texture as for example Tilsit. Also cheeses with another texture may be produced in this manner.

According to the other method the milk is pre-treated and concentrated by way of ultrafiltration possibly followed by evaporation. The concentrated milk is together with rennet filled into moulds where coagulation takes place.

In FR 2 052 121 and DE-OS 29 32 767 there is described among other things such methods without cutting of the coagulum.

According to the first mentioned method, which comprises cutting of the coagulum one aims at achieving as high a concentration as possible of milk proteins in the milk and consequently also in the curd when the cutting takes place. The reason for this is that one wants to make use of the basic material as much as possible. The less the concentration of the curd differs from cheese to be produced the less whey is drained away and the less whey proteins are lost. Hitherto it has not been considered possible to produce cheese according to this method in many connections. In SE 427 407 there is said in the example that the milk is ultrafiltrated to a dry substance of 27 %, which corresponds to about 15 % solids non fat (SNF).

In US 3 945310 it is said "It has been found that certain characteristics of the curd obtained are closely associated with the non-fat solid substance of the ultrafiltrated milk. Thus, if the non-fat solid substance content of this ultrafiltrated milk is greater than 15 % by weight, the curd will not readily reintegrate, in other words if this curd is fragmented it will be difficult to obtain a homogenous curd mass from several fragments. By contrast, If the non-fat solid substance content of the ultrafiltrated milk is less than 15 % by weight, it is possible to cut the curd into slabs of suitable size and to reconstitute the homogenous curd mass from the slabs by Introducing them for example into a draining mould in which they spontaneously reintegrate."

Now It has been proved possible to overcome this limitation, which earlier has been accepted by experts, regarding the possibility to produce cheese from highly concentrated milk through a dramatic deviation from the usual cheese making art.

The expert knows that after addition of rennet, that is chymosin or some other corresponding enzym, to the milk at a suitable temperature an enzymatic hydrolysis of kappa-casein starts. When the largest part of the kappa-casein around a casein micelle has been hydrolized, the casein micelle starts to take part In an aggregation process. Already very soon during the aggregation it will be detectable in microscope as a precipitation of the casein aggregate in the milk or as an increase in the viscosity of the concentrated milk. The interval in time between addition of rennet and this microscopically detectable change is called rennet clotting time RCT. This is a characteristic parameter when producing cheese. Approximately it can be said that the mechanical properties of the coagulum depend on a multiple of RCT, even if the magnitude of this value varies depending on a change in the added amount of rennet, the temperature, the way the milk has been pretreated and a possible addition of CaCl₂.

Usually the coagulum is cut when the largest part of the casein micelles are enclosed in the three-dimensional network which constitutes the coagulum. The coagulum is cut earliest at 1,8 RCT and usually at 2-3 RCT.

It has now been found that this prior technical knowledge is not suitable for cutting and moulding of coagulums from milk, which has been ultrafiltrated to a high concentration. Unexpectedly it has been found that in order to obtain a good reintegration of the curd after moulding it is Important to base the time for cutting not on a multilpe of RCT but on the mechanical properties of the coagulum after a certain time. In this way the coagulum is cut at a time when it is much softer than has earlier been considered right. According to the invention it is proposed that the coagulum is cut already before it has a firmness correspending to 300 g measured on a Stevens Texture meter, after which the cut coagulum is immediately transferred to the cheese moulds for moulding.

Since it is difficult to define the degree of forming of the network in the coagulum in chemical terms it is suggested that the firmness of the coagulum is defined by way of measuring on a Stevens Texture meter. Of course it is possible to make this measurement on some other instrument but the values of different instruments are not directly comparable. The method of measuring on a Stevens Texture Meter is described in a monograph "Food Texture and Viscosity": Concept and Measurement by Malcolm C. Bourne, 1932, Academic Press, New York, pag 131-133.

The following is a citation from the monograph.

"The Stevens Texture LFRA Texture Analyzer.

This instrument, developed by the Leatherhead Food Research Association (LFRA) in England, was designed to perform the standard Bloom test plus a number of other tests. The instrument stands about 50 cm high, 24 cm wide, and 23 cm deep, and weighs about 12 kg (see Fig. 6). It replaces the Boucher Electronic Jelly Tester, which is no longer manufactured.

The standard probe is a 1/2-in.-diam flat-faced straight-sided acrylic punch that has the same dimensions as the punch used for the Bloom test. Punches of other diameters and punches in the form of a needle, ball, or blade are also available. Four speeds of punch travel are available: 12, 30, 60, and 120 mm rnin^-1. The maximum stroke of the punch is 15 cm. The penetration distance is adjustable from 1 to 29 mm in 1-mm steps. In operation, the test sample is placed beneath the punch and the motor activated. The punch moves downward at the maximum speed until a force of 5 g is registered, when it automatically steps down to the selected set speed and travels at this speed for the selected distance. At the end of the stroke it returns to its original position at maximum speed. An electronic load cell in the base of the instrument senses the force and registers it on a digital readout, which shows the maximum force obtained in the test. The instrument has a capacity of 1000 g force and reads within 1 g. It can be adapted to a 100-g force capacity and a reading within 0,1 g for very soft products. A recorder is an optional accessory giving force-distance plots of the puncture tests. This Instrument is a useful general- purpose puncture tester for soft products. It is used on meat pastes, foams, various gels, and some fats."

In this case it has been found suitable to use a cylindric body with a diameter of 50 mm which Is pressed against the coagulum with a penetration speed of 2 mm/s at a temperature of 38°C. When the body has penetrated 9 mm the force which has been needed to press the body to this depth is measured. Surprisingly it has been found that if the firmness of the coagulum is measured in this way there is obtained at a deflection of 300 g the highest value of the firmness of a coagulum which, if the cutting and moulding is carried through immediately thereafter, melts together to a coherent mass, with its own weight as a pressing force.

When carrying through the method according to the invention the milk is concentrated such that the content of non fat solids is more than 16 weight percent. Earlier it has not been possible to produce cheese from milk with such a high concentration of non fat solids since the curd does not melt together when being pressed with self pressure. The invention consequently implies an important step forward in the cheese making art.

According to the invention milk which has been concentrated by way of ultrafiltration is used with advantage. If it should be considered desirable to concentrate the milk for example by way of ultracentrifugation or ion exchange chromatography such milk may also be used.

According to the method of the invention the nutritive substances in the milk may be made use of to a much higher degree than earlier, since the concentration of the concentrated milk to a larger extent corresponds with the concentration of the cheese. With such a high content of dry substance a very small amount of whey Is drained off and very few small cheese grains disappear with the whey.

In order to precipitate the casein rennet is usually used, but the method according to the invention may of course be used for production of cheese which is coagulated with acid.

The method according to the invention may suitably be used when producing cheese continuously according to the method described in SE 427 407 but of course it is also possible to use the method when producing cheese in batches.

When the coagulation takes place continuously a milk sample which is concentrated to a suitable degree is coagulated and depending on this measurement the usual time in the coagulator is determined.

The cut cheese curd is pressed In the cheese moulds by means of self pressure. Usually the milk is pasteurized before the ultra filtration in order to ensure a good bacteriological quality.

According to the method of the invention a high temperature treatment of milk or milk concentrate may be carried through prior to the renneting. With such a treatment a soft coagulum is obtained, the water retaining capacity of the cheese is increased and the yield of the cheese increases, since the amount of protein which should otherwise have been lost in the whey diminishes. Such a high temperature treatment may last during 3 minutes at a temperature of 95°C.

The method according to the invention is described further in the example below describing production of cheese of Feta type. Example

Pasteurized milk (78°C/15 seconds) with 2,5 % fat and 3,4 % protein is concentrated by way of ultrafiltration to a concentrate with an increased content of non fat solids namely 14,5, 19,8 and 29 weight percent. To each of these concentrates there is added 25 ml/100 1 concentrate standard rennet (Chr Hansens Lab., Copenhagen) and 1 % starter culture. The concentrates are then pumped into a continuous coagulator. In a number of trials the time, before which the concentrate was pumped out from the coagulator and through the cutting head, was varied. The coagulum was cut in curd grains with a largeness of 10 x 10 x 10 mm, which immediately after were transferred to a Havarti cheese mould. The cheese moulds were turned after 4 and 12 hours. After 24 hours the reintegration was judged.

In parallel to the trials mentioned above samples of 380 ml were taken from the concentrated milk to which samples rennet and starter culture were added. The samples were held at a constant temperature of 38°C. After the same times the firmness of the curd was determined In the way which has been described above. The result may be seen in the figure. It is shown that a good reintegration of the curd grains Is obtained only when the coagulum Is cut at a temperature when the firmness of the curd is sufficiently low, which measured on a Stevens Texture meter means under 300 g.

In the figure there is also shown an example of the firmness of the coagulum of a cheese mass which has been produced from milk with a content of non fat solids of 8,9 weight percent.

As may be seen in the figure only a firmness of the coagulum of 100 g was obtained at this content of solids. At this concentration a good reintegration of the coagulum is obtained but the yield of milk protein is bad.

Claims

Claims

1. Method for producing curd from concentrated milk, which is renneted, is brought to coagulate, is cut, is filled into moulds and after treated in a usual manner, c ha r a c t e r i z e d i n that the milk is concentrated to a content of non fat solids of at least 16 %, which concentrate is renneted, after which the obtained cheese curd is cut already before the coagulum has a firmness corresponding to 300 g measured on a Stevens Texture meter at a temperature of 38°C and is thereafter immediately transferred to the cheese moulds.

2. Method according to claim 1, c h a r a c t e r i z e d i n that the milk is concentrated by way of ultrafiltration.

3. Method according to any of the preceding claims, c h a r a c t e r i z e d i n that the cheese curd is brought to coagulate in a continuous coagulator.

4. Method according to any of the preceding claims, cha r a c t e r i z e d i n that the cut cheese curd in the cheese moulds is pressed by way of self pressure.

5. Method according to claim 1, c h a r a c t e r i z e d i n that the milk or the concentrate is pasteurized at a high temperature prior to the renneting.