Sweet cream butter
When sweet cream butter with a pH of around 6.5 is to be processed and no “chemical agents” (e.g. citric acid) are allowed to be used for denaturing the proteins, the emulsion layer has to be taken into account.
Centrifugation and destruction of this layer can only be carried out by specially designed separators and phase inversion. The operating method of the separator has a decisive influence on the process, the required additional equipment and the efficiency of the installation. For processing sweet cream butter, it is necessary to use a separator which allows concentration to 99.5 percent fat. The emulsion has to be discharged with the serum phase.
The melted butter, e.g. melted with the BXA, is generally pumped directly into the high fat tank. The butter blocks are taken from cold storage at, for instance -20 °C, and are melted in the melting system. The product temperature in the buffer tank, depending on the design of the plant, is between 45 and 65 °C. The temperature of the product is raised to 70 – 75 °C in a plate heat exchanger.
Phase inversion by means of a homogenizer is required to minimise the emulsion phase. The oil concentrator achieves separation of 99 percent fat. The heavy phase, a mixture of butter milk and residual emulsion particles, is fed to a skimming separator.
The oil phase (light phase) is heated to about 90 °C and then separated again in a further separator. Before the oil is fed to the polishing separator, wash water is added to improve the quality of the oil.
The further process steps are comparable with those of the processes already described. Since no cream concentrator is present, secondary skimming of the serum phase after the oil concentrator is highly recommended. When sour cream butter with a pH of 4.6 to 4.5 and with an increased protein content is to be processed, a decanter can be used. Separate concentration of the solids is possible.
In any case, a separator (polishing separator) has to be installed downstream to increase the fat concentration to 99.5 percent.
The amount of salted butter used as a raw material for the production of butter oil in recent years has risen steadily. The salt content is removed together with the butter milk during centrifugal separation. The salt concentration in the butter milk increases to approx. 10 percent if the original salt content of the butter was 2 percent for example. Further processing of the salted butter milk is limited.
The emulsion phase in salted sweet cream butter can also be “broken” by the addition of citric acid. At the same time, the protein in the butter is denatured. Thetreated raw material then behaves in the same way as sour cream butter.
The melted butter is brought to a pH of 4.5 – 4.6 by the addition of acid. At this pH, not only the free protein is denatured; in addition, due to the alteration in the intact fat-globule membrane protein, the membrane is broken open and the emulsion is destroyed. An easily decantible sediment is then obtained in addition to a clear water and oil phase. In contrast to “real” sour cream butter, this sediment content is significantly lower. One reason is that the fat-free dry matter (part of which consists of protein) is less in the case of sweet cream butter than is the case with sour cream butter.
Acid is added, and the product is heated to a temperature of 70 – 75 °C; an adequate reaction time is then allowed.
The oil is then concentrated in the oil concentrator to approx. 99 percent. The oil is heated to approximately 90 °C in the plate heat exchanger, and it is then concentrated to 99.5 percent in the oil polishing separator. It is necessary to add wash water upstream of the separator so that residual salt particles in solution can be washed out.
Care must be taken to ensure that the pH does not rise again when the wash water is added. The wash water should thus be adjusted to a pH of 4.5 – 4.6 with acid before it is added to the product.
The final value of the oil of 99.8 percent is adjusted in the downstream vacuum evaporator. For processing salted butter, it is extremely important to ensure that all parts of the installation which come into contact with the product are made of special corrosion-proof materials.
Sour cream butter
Sour cream butter is produced from biologically acidified cream. The pH value of the butter is between 4.5 and 5.2 depending on the country of origin.
Processing of sour cream butter into butter oil is generally the least expensive method. This is however only partly true when the pH is between 4.7 and 5.2.
When sour cream butter is processed, a third liquid phase (emulsion phase) is not present, as has already been stated. The most important criterion for the design of the plant is that the separable solids (denatured protein because of the low pH value) can amount to as much as 2 percent absolute. In general, the value is between 1.3 and 1.5 percent DS.
For processing from sour cream butter, it is particularly important to ensure that the melting process in the melting system is gentle, as localized overheating will relatively quickly lead to protein burning. The product leaving the butter melting system at a temperature of 45 – 55 °C is heated in the plate heat exchanger to 70 – 75 °C, and is then pumped to the 3-phase decanter. The oil is concentrated in the decanter to 95 – 98 percent, and is heated to approximately 90 – 95 °C; it is then brought to a concentration of 99.5 percent in the oil polishing separator. The residual moisture content is reduced to less than 0.1 percent by evaporation in the vacuum evaporator. The serum phase generally has a fat content of less than 0.8 percent; accordingly, if we consider the amount obtained (10 – 12 percent of the amount of raw product), fat recovery is only worthwhile if daily quantities are high. The decantible solids are concentrated in the decanter to 20 – 45 percent DS as required, and are then fed from the decanter discharge to the tank. The solids consist mainly of denatured protein. In addition, a fat in DS of 2 – 5 percent must be expected. The oil-enriched heavy phase from the oil polisher is recycled back into the process.
It is necessary to add water upstream of the oil polishing separator in order to ensure optimum “washing out” of the residual protein, and also at the same time to stabilize the separation zone in the bowl of the oil polishing separator in the required position.
For further utilization, the denatured protein discharged by the decanter can be converted into a stable soluble state.
As already mentioned, when butter with high initial FFA values is processed, butter oil can still be obtained by saponification of the short-chain fatty acids, followed by separation of the resulting flocculate.
A suitably prepared wash water (pH > 11) is added to the flow of oil upstream of the oil polishing separator. The free fatty acids come into contact with the basic water, are saponified and are simultaneously washed out. The wash water with the free fatty acids is separated from the oil in the oil polishing separator. The oil leaving the oil polisher then meets IDF standards with respect to FFA values for anhydrous butter oil.
Before “wash water with caustic” is added, the oil must have a concentration of more than 99 percent fat.