GB2168591A - Heat sterilisation of natural cream of milk - Google Patents

Abstract

A process for the continuous treatment of a flow of natural cream of milk by heat sterilisation and homogenisation, wherein the cream is sterilised by indirect heat at a temperature between 125 DEG and 142 DEG C, then homogenised at a temperature between 60 DEG and 0 DEG C and then packaged in hermatically sealed containers at a temperature not exceeding 5 DEG C.

Description

SPECIFICATION Process for the continuous treatment of natural cream of milk by sterilisation The present invention relates to a process for treating natural cream of milk, comprising sterilisation by heat.

Natural cream of milk is an emulsion of fat in water, usually containing 20-40% by weight of fat and 70-55% by weight of water (the remainder consisting of natural substances such as proteins, salts, etc.). It is also known that cream obtained by the process of surface skimming contains more water than cream obtained by centrifuging. Whatever the case, natural cream of milk can be preserved only for a very short period of time. Cream obtained by pasteurisation keeps for 3 to 4 days, whereas cream sterilised by means of heat keeps for at least 60 days.

One of the important uses of cream of milk is the preparation of whipped cream, whether it be on an industrial or artisanal scale, or for domestic usage. From one volume of natural fresh cream, it is possible to obtain two volumes of whipped cream and the swelling ratio is therefore 2:1.

Pasteurised cream is generally obtained by means of preliminary degassing of the natural cream at a temperature greater than 60"C, followed by pasteurisation at 85-95"C. Pasteurised cream "swells" fairly well and, because of this, is generally chosen by users of whipped cream. However, its short preservation time means that consumers must be frequently supplied and consequently gives rise to high distribution costs. Moreover, pasteurised cream is subject to changes in colour, smell and taste, which are immediately perceptible, compared to natural fresh cream.

Cream which has been sterilised by heat is almost always structurally unstable. In fact, the fatty phase tends to coalesce so as to form a dense floating mass in the aqueous phase of the original emulsion; this transformation is irreversible and the product thus transformed can no longer be used for the preparation of whipped cream. The stability can be improved within certain limits by the addition of additives, but then it is no longer possible to speak of "natural" cream. So as to obtain a natural cream with improved stability, the manufacturers have resorted to homogenisation of the already sterilised cream, consisting in passing the cream, at a temperature higher than 60"C, through a narrow passage, under a supply pressure of at least 30 bars, up to approximately 250 bars.

However, as far as the production of whipped cream is concerned, the product thus obtained is practically unusable since its volume increase ratio barely reaches 1.5 1, its consistency being insufficient. Moreover, in this case, it is also possible to note a considerable deterioration in the organoleptic properties.

In the same was as the pasteurisation processes, the known sterilisation processes also require a stage involving degassing of the cream of milk before sterilisation so as to eliminate the oxygen (air) which is present in the fresh cream of milk. This stage involves high installation and operating costs, both on account of the cost of the degasser and as a result of the need to maintain a completely aseptic environment inside the degasser.

Moreover, degassing gives rise to undesirable concentration of the cream following the inevitable loss of water which the cream of milk undergoes due to evaporation.

The object of the present invention is to reduce drastically, or even overcome, the abovementioned drawbacks in particular, without the use of additives or other foreign substances.

Surprisingly it has been discovered that, by performing homogenisation of the sterilised cream in special conditions, the abovementioned object can be achieved, avoiding, moreover, the need for a degassing stage and thus reducing considerably the installation and production costs.

The present invention thus provides a process for the continuous treatment of a flow of natural cream of milk by heat sterilisation and homogenisation, characterised in that the flow of natural cream is sterilised by indirect heat at a temperature lying between 125 and 142"C, then directly homogenised at a temperature between 60"C and 0 C and then packaged in hermetically sealed containers at a temperature not exceeding 5"C.

The cream of milk used in the treatment according to the invention is a natural cream from whole milk, free from additives and having preferably a water content of 65% to 55% by weight and a fat content of 30% to 40% by weight, the remainder consisting mainly of protein substances, lactose and mineral salts.

Sterilisation is performed preferably during a period of 1 to 5 seconds.

The homogenisation phase is performed, preferably, by drawing in a valve-type homogeniser under a supply pressure of between 30 to 80 bars and preferably of 50 bars.

Preferably, the temperature during the homogenisation phase lies between 40"C and 50"C and is preferably 44"C.

The process according to the invention will be described below with reference to the attached drawing which shows, in diagrammatic form, a plant for implementing this process.

In the drawing, the reference numeral (1) designates a sterilising apparatus supplied, via the pipe (2) and the positive-displacement supply pump (3), with a continuous flow of natural milk of cream, at a storage temperature of approximately 5"C. Sterilisation in the apparatus (1) is performed by means of indirect heat provided by a heating fluid such as, for example, hot water or superheated water, and the said apparatus (1) consists, prefera bly, of a heat exchanger of the plate type.

The sterilisation temperature lies between 125"C and 142"C and is chosen in accordance with the preservation time required for the final product which one wishes to obtain.

The periods of exposure at the supply temperature last, preferably, 1 to 5 seconds, these periods generally being indirectly proportional to those at the chosen temperature.

Preferably, the apparatus (1) is provided with a preheating section in which the flow of cream of milk is brought to a temperature close to that of sterilisation.

The flow of cream of milk leaving the apparatus (1) via the pipe (4) is then cooled in a plate heat exchanger (5) to a temperature lying between 60"C and 0 C and preferably lying between 40"C and 50"C. Advantageously, the exchanger (5) can form a section of the sterilising apparatus (1), in which section the heat contained in the hot flow of cream of milk is recovered by means of heat exchange due to the cold flow of cream supplying the sterilising section.

The flow of cream leaving the exchanger (5) supplies, via the pipe (6), a homogeniser (7) comprising a high-pressure pump (8) and a drawing device (9), preferably of the valve type.

The high-pressure pump (8) brings the flow of cream to the supply pressure of the drawing device, which is preferably between 30 and 80 bars and is preferably 50 bars.

The homogenisation temperature lies between 60"C and 0 C and preferably between 40"C and 50"C.

The flow of cream leaves the homogeniser via the pipe (10) and is conveyed to an aseptic packaging machine (12) where it is packaged in sterilised and hermetically sealed containers (18) at a temperature not exceeding 5"C. Preferably, the storage time between homogenisation and packaging is less than 10 seconds.

If the homogenisation temperature used is higher than the packaging temperature, the flow of homogenised cream passes through a heat exchanger (11) located on the pipe (10), where it is cooled to the packaging temperature which must not exceed 5"C and is preferably 2"C.

The cream of milk obtained following treatment according to the invention has a swelling ratio, as mentioned above, which is greater than 2 : 1, both immediately after treatment, and after a period of preservation, even when this is longer than 60 days. The whipped cream obtained, moreover, has a high and lasting consistency, that is to say it does not decrease in volume 2 days after the whipping operation if it is kept at refrigeration temperature.

The cream treated as described above is very white in colour and has a homogeneous appearance and pleasant smell and taste, quite similar to that of natural fresh cream. These properties remain constant even after preservation for 60 days in sealed containers.

EXAMPLE Fresh natural cream of whole milk was used, this cream being obtained by centrifugal skimming and having a fatty matter content of 37% by weight and a water content of 57% by weight.

This cream flowing at a rate of 0.75 litres and at a temperature of 5"C is introduced into a plate heat exchanger comprising a sterilising section and a cooling section, with recovery of the heat.

Sterilisation is performed at a temperature of 140"C by indirect heating using superheated water for a period of 2 seconds at the abovementioned temperature.

The flow of cream leaving the sterilising section is rapidly cooled to a temperature of 44"C in the cooling section of the said plate exchanger and, from where, homogenised at a temperature of 44"C and at a pressure of 50 bars in a Gaulin valve-type homogeniser, Model MC 45, manufactured by the company Gaulin Corp. (U.S.A.).

The flow of homogenised cream is then cooled to a temperature of 4"C in a plate exchanger and then immediately packaged, in aseptic conditions, in sterilised and hermetically sealed containers. More precisely, the time lapsing between homogenisation and packaging is 5 seconds and the overall treatment time is approximately 100 seconds.

The cream thus treated was subjected to whipping tests and tests for checking the physical and organoleptic-properties. For these tests, use was made of samples of cream taken both immediately after packaging and after preservation for 60 days at the refrigeration temperature of 4"C.

When the containers were opened, in both cases the cream had a very white and homogeneous appearance and did not have an unpleasant smell or taste.

The whipped cream obtained had, in each case, a swelling ratio equal to or greater than 2.35. The consistency of the whipped cream, determined using Mohr's apparatus, had an average value of 45 units according to the scale on this apparatus.

Tests as to stability during dripping were performed at an ambient temperature of 21"C by placing cubes of whipped cream, with a side length of 10 cm, on a grid and recovering the whey lost by a cube following dripping. Only 3 ml and 5 ml of whey were recovered after an exposure time of 1 hour and 2 hours respectively. After two days at a temperature of 5"C, all the cubes of cream showed a decrease of less than 1 cm, thus demonstrating excellent stability.

Claims (6)

1. Process for the continuous treatment of a flow of natural cream of milk by heat sterilisation and homogenisation, characterised in that the flow of natural cream is sterilised by indirect heat at a temperature lying between 125 and 142"C, then directly homogenised at a temperature between 60 C and 0 C and then packaged in hermetically sealed containers at a temperature not exceeding 5"C.

2. Process according to Claim 1, characterised in that the flow of cream is subjected to sterilising temperatures for a period of 1 to 5 seconds.

3. Process according to Claim 1 or Claim 2, characterised in that the temperature during the homogenisation phase lies between 40"C and- 50 C and is preferably 44"C.

4. Process according to any one of the preceding Claims, characterised in that homogenisation is performed by drawing in a valvetype homogeniser, under a supply pressure between 30 and 80 bars and preferably of 50 bars.

5. A process for the continuous treatment of a flow of natural cream of milk by heat sterlisation and homogenisation, as claimed in Claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

6. A process substantially as hereinbefore described with reference to and as shown in the accompanying drawing.