Skimmed Milk Research Paper

Unit operations in butter making

The flowsheet of the manufacturing of cultured butter is shown in figure 1. In this section, the unit operations used for the manufacturing of butter and their contributions to its quality are described.

1 Skimming

The milk received from the farmer is first separated into cream and skimmed milk. This is done by centrifugal forces to increase efficiency and decrease processing time compared to using the gravity force. The skimmed milk is separated from the milk fat to enhance several economic aspects (Walstra et al. 2006a):

• Separation of skimmed milk will decrease the buttermilk yield from the butter manufacturing; therefore the skimmed milk can be used elsewhere for dairy production.

• The manufacturing equipment

Temperature treatment regulates the amount of solid fat; this is the major factor that determines the consistency. The consistency of butter is one of the most important quality characteristics.

This phase is carried out in ripening tanks. Heating and cooling are done very gradually. The treatment programme will depend on the iodine value. Fat with a high iodine value, meaning there is a high degree of unsaturated fat, produces greasy butter. Butter of acceptable consistency can be obtained from both hard fat and soft fat. The iodine value can be from 28 - 42. For hard fat the process is as follows:

Cooling to 8°C and storage for 2 hours. Then gentle heating to 20 – 21°C and storage at that temperature for 2 hours. For water at maximum of 27°C is used for heating. Cooling to 16°C and then to churning temperature. Cooling to 8°C will start the formation of mixed crystals that bind fat from the liquid phase. Cream is gently heated to 20 – 21°C, the majority of mixed crystals melt. This leaves pure crystals of fat with a high melting point. During storage at 20 – 21°C the melted fat crystals recrystallize, forming pure crystals. When the temperature is reduced to 16°C, the melted fat continues to crystallise and form pure crystals. During the holding period all fat with a melting point of 16°C or higher will crystallise. The treatment

This step will be done differently if the churning is made batch-wise or continuously. In a batch process, the churning is stopped once the correct size of the butter grains have been achieved. (Gösta Bylund (2003) The buttermilk is therefore drained out. In a continuous process, the buttermilk is drained continuously and is recirculated into the churning process as a washing step. In both ways, the butter grains need to be large enough to allow a good separation of the buttermilk. If not, an additional step of washing could be done by mixing the grains with cold water. However nowadays this step is only processed if the temperature needs to be controlled (Walstra et al.