Fractionation of fat 215 chamber to recreate a self-feeding system using upper chamber vacuum level, and on completion of each filtration cycle the vacuum in each chamber was released, and the upper chamber opened by lifting up, allowing the band to be indexed forward to its ischarge. A stainless steel wire, fixed along the width of the band, ensured that the cake was dislodged from the filter paper and dropped into the heated trough in front of the filter. When the cake liquefied it was transferred via a butterfly valve at the base for packaging or texturisation for food use. The filtrate(olein) drawn under vacuum during filtration, was transferred via an intermediate vacuum tank, filtrate receiver, into the filtrate storage tank before being drummed. The most suitable filtration medium was found to be Paper/ Binzer Type 67/N, 80 g, roll, 0.108 m in width and approximately 200 m in length, of bleached crepe quality The yields for milk fat were typically 76-80%o, Table 8.1, compared to 67-72% (Deffense, 1985)for the Florentine filter. This is attributed to the improved efficiency achieved by using the integral, vacuum sealed, upper chamber. The fastest crystallisation rate was established as 6Ch-l, cooling down to 28 C for satisfactory filtration Laboratory analyses carried out on milk fat fractions from vacuband filtration are given in Table 8.1(Rajah, 1988). Comparative results on products using rotary drum membrane press filter are given in Table 8. 2(Kokken, 1992). (Note: The ' Drop pointis a measure of the melting point of the oil or fat relating to the temperature at which an oil drop falls freely when a solidified sample is warmed in a cup with a small hole. The multi-step fractionation of milk fat was also carried out using the vacuband filter In this type of process the oleins from successive fractionations are used as feed for further fractionation. Typically, the quantity and size of crystals is maximised when oleins are cooled to temperatures of between 2 and 5C below their melting point. Using this route, two, three- and four-step fractionations have been completed satisfactorily, Table 8.3(Rajah, 1988). In low temperature fractionations it is important to ensure that environmental temperatures are carefully controlled and that all contact surfaces for the crystal slurry are held at the temperature of separation. Low melting point milk fat olei can be used in food applications where only liquid oils are normally used, e.g mayonnaise(Rajah et aL, 1984) 8.2.2 Rotary drum filter De Smet supply complete fractionation plants incorporating the'Stockdale type rotary drum filter The crystallisation step is quite rapid, an average maximum of a 6 h cooling cycle is common. However, in order to ensure efficient and effective crystallisation the design of he crystallisation tank has to include a large cooling surface with good agitation facilit Typically, industrial crystallisers capable of holding up to 25 m3 product are presently available with these features. To achieve homogeneous supersaturation of the oil during cooling and even temperature throughout the mass of the oil, the distance between each crystal and the cooling surface must be minimised to enable the efficient dissipation of he heat of crystallisation. For this reason the use of a two-speed motor, with variable speed gearbox, or if possible a continuous variable-speed motor, is proposed to drive the agitator. At the start of the process when the oil is in the molten state, at higher temperature(65-70.C), maxim m agitation increases heat transfer andFractionation of fat 215 chamber to recreate a self-feeding system using upper chamber vacuum level, and on completion of each filtration cycle the vacuum in each chamber was released, and the upper chamber opened by lifting up, allowing the band to be indexed forward to its discharge. A stainless steel wire, fixed along the width of the band, ensured that the cake was dislodged from the filter paper and dropped into the heated trough in front of the filter. When the cake liquefied it was transferred via a butterfly valve at the base for packaging or texturisation for food use. The filtrate (olein) drawn under vacuum during filtration, was transferred via an intermediate vacuum tank, filtrate receiver, into the filtrate storage tank before being drummed. The most suitable filtration medium was found to be Paper/Binzer Type 67/N, 80 g, roll, 0.108 m in width and approximately 200 m in length, of bleached crepe quality. The yields for milk fat were typically 76-80%, Table 8.1, compared to 67-72% (Deffense, 1985) for the Florentine filter. This is attributed to the improved efficiency achieved by using the integral, vacuum sealed, upper chamber. The fastest crystallisation rate was established as 6°C h-', cooling down to 28°C for satisfactory filtration. Laboratory analyses carried out on milk fat fractions from vacuband filtration are given in Table 8.1 (Rajah, 1988). Comparative results on products using rotary drum and membrane press filter are given in Table 8.2 (Kokken, 1992). (Note: The 'Drop point' is a measure of the melting point of the oil or fat relating to the temperature at which an oil drop falls freely when a solidified sample is warmed in a cup with a small hole.) The multi-step fractionation of milk fat was also carried out using the vacuband filter. In this type of process the oleins from successive fractionations are used as feed for further fractionation. Typically, the quantity and size of crystals is maximised when oleins are cooled to temperatures of between 2 and 5OC below their melting point. Using this route, two-, three- and four-step fractionations have been completed satisfactorily, Table 8.3 (Rajah, 1988). In low temperature fractionations it is important to ensure that environmental temperatures are carefully controlled and that all contact surfaces for the crystal slurry are held at the temperature of separation. Low melting point milk fat oleins can be used in food applications where only liquid oils are normally used, e.g. mayonnaise (Rajah et al., 1984). 8.2.2 Rotary drum filter De Smet supply complete fractionation plants incorporating the 'Stockdale' type rotary drum filter. The crystallisation step is quite rapid, an average maximum of a 6 h cooling cycle is common. However, in order to ensure efficient and effective crystallisation the design of the crystallisation tank has to include a large cooling surface with good agitation facility. Typically, industrial crystallisers capable of holding up to 25 m3 product are presently available with these features. To achieve homogeneous supersaturation of the oil during cooling and even temperature throughout the mass of the oil, the distance between each crystal and the cooling surface must be minimised to enable the efficient dissipation of the heat of crystallisation. For this reason the use of a two-speed motor, with variable￾speed gearbox, or if possible a continuous variable-speed motor, is proposed to drive the agitator. At the start of the process when the oil is in the molten state, at higher temperature (65-7OoC), maximum agitation increases heat transfer and consequently