Sterilized Cream

It is also known as Table cream. The objective of preparation of sterilized cream is to prolong the shelf life of cream and make it available to the consumers in a ready-to-use form and in good condition. Sterilized cream should be smooth and free from lumpiness and separation of serum. The high heat treatment, however imparts it a peculiar flavour. Homogenization increases its viscosity. The whipping quality of sterilized cream is also poor. The fat content in sterilized cream ranges between 20-25 % and solids-not-fat content between 6.5-9.5 %.

 

Manufacturing steps

Flow diagram for preparation of sterilized cream

 The steps involved in preparation of sterilized cream are given in fig. Selection of cream: Fresh and sweet cream is collected for the preparation of sterilized table cream. The percent titratable acidity (TA) of freshly separated cream is always lower than that of the milk from which it has been separated.

The T.A can be calculated by the following formula:

Percent T.A. of cream=(Percent serum in cream)/(Percent serum in milk) x Percent T.A of Milk
                                      

                    = (100 – Percent fat in cream)/(100 – Percent fat in milk) x Percent T.A of Milk
                                        
Standardization: Standardization refers to the adjustment of milk fat level in cream to the desired level i.e. conforming to the standards requirement. The fat level(percent) in cream is usually adjusted or decreased to the desired level by addition of calculated quantity of skim milk. The quantity of skim milk to be added to cream is calculated by the Pearson’s square method as explained below (Fig)

Pearson’s Square

Let us assume that the fresh sample of cream contains 40 percent fat. It is required to reduce its fat to 20 percent. The available skim milk for standardization contains only 0.1 per cent fat.

The required quantity of skim milk to be added to cream is calculated as follows by drawing a square and writing the fat percentage of cream (40%) and skim milk(0.1%) on the two corners on the left side of the square.

(i) The desired fat percent level (20%), in cream is written in the centre of the square.

(ii) Now subtract the number in the centre (20) from the larger number (40) at the left-hand side of the square and place the remainder (20) at the diagonally opposite right-hand corner.

(iii) Again subtract the smaller number (0.1) on the left hand side from the number in the centre (20) and place the remainder (19.9) at the diagonally  opposite right-hand corner.

The numbers on the right-hand side now represent the number of parts of cream and skim milk to be mixed to obtain cream containing 20% fat. It means that if 19.9 parts by weight of cream containing 40% fat is blended with 20 parts by weight of skim milk (0.1% fat) will yield cream containing 20% fat.Pre-heating: The purpose of pre-heating of cream is to delay its spoilage during subsequent processing steps. Pre-heating inactivates undesirable micro-organisms and the enzymes particularly lipase. It also helps in efficient homogenization of cream. Standardized cream is pre-heated by heating it to 80-90°C without holding.

Homogenization: The purpose of homogenization of cream are as follows:

i) To prevent rising of fat during sterilization and storage.

ii) To prevent formation of a fat plug in the container.

iii) It also improves taste, whipping power and flocculation stability of the product.Flocculation of coffee cream is a major problem. When cream is added to hot coffee, flocculation occurs mainly because of the precipitation of casein.Homogenization of casein free cream enriched with whey protein and pre-heated to 90°C for 5 min. improves the flocculation stability probably because of whey-protein denaturation.

Homogenization of pre-heated cream at 80-90°C is carried out in two stages employing homogenization pressure of 25-30 kg/sq cm in first stage and 5kg/sq cm in the second stage. In the first stage the fat globules are sub-divided in smaller size globules and distributed uniformly in the whole mass of cream; it increases viscosity. The second stage reduces viscosity and prevents the fat globules from clumping together and forming lager clusters. Clumping refers to the tendency of fat globules to loosely adhere to one another to form clusters. The tendency of clumping is influenced by the following factors.

i) Fat Globule size - Large fat globules clump more readily than smaller ones.

ii) Temperature - Clumping tendency decreases with increase in temperature.

iii) Agitation - It increases clumping tendency at lower temperature (7°C) while at higher temperature (60°C) the tendency of clumping decreases.

iv) Separation Method - Gravity separation yields cream with increased tendency of clumping than that obtained by centrifugal separation with the same fat content.

v) Adhesive - Addition of adhesive helps in clumping.

Cooling: Since filling of cream in the containers requires holding of cream for sometime there is every possibility of increase in the titratable acidity of cream.This may cause problems during sterilization process. Therefore, it is essential to cool the cream to about 15-16°C to prevent any change in the acidity of cream if the manufacturer requires enough time to fill the cream in containers in good condition and seal them. However, if filling and sealing do not require holding of cream, it can be filled directly from the homogenizer in to the containers and transferred immediately to the sterilizer. Thus, it does not require cooling.

Filling and Sealing: Homogenized cream is filled in containers (lacquered tin cans,glass bottles, retortable pouches etc.) leaving minimum head space and sealed.These containers are then transferred to the sterilizer.

Sterilization: Sterilization of cream improves the shelf life of cream by making it free from viable organisms. In-can sterilization of cream is done in retorts. The filled cans or bottles are packed in retorts/batch sterilizer and then heated allowing 15 minutes for coming up time to desired temperature (118°C), 12-15 minutes holding time at 118°C and 15 minutes for cooling to room temperature. Thus, it takes 45 minutes to complete one cycle of sterilization process for one batch. After completion of the process the tins/bottles are cleaned and tested for leakage by a immersing them in clean water. Leaking tins/bottles are then discarded separately.

Storage and Distribution: The leak proof tins/bottles or packages are staked properly in cardboard cartons and stored at room temperature. Properly sterilized cream is expected to keep good for few months.