Tirtiaux process

The main commercial fractionation process for milk fat is the Tirtiaux process, followed by the De Smet process. There are also some proprietary variations of the dry fractionation process which enable the production of various milk fat fractions. The characteristics of the fractions obtained are affected by many factors, including the equipment design, the associated process, the initial temperature of the molten fat, the crystallization conditions (e.g., degree of initial supercooling), the rate of subsequent cooling and agitation after crystallization commences, the final temperature of fractionation and the method used to separate the fractions. 

Commercially, separation is mostly performed by vacuum filtration on belt or drum filters or by pressure in membrane filters (Illingworth, 2002). Evenly-sized well-developed spherical crystals, such as those obtained in a well-executed Tirtiaux process, can be easily recovered using vacuum filters. For optimal filtration, the air on top of the filter may be cooled or heated to the filtration temperature to avoid melting or crystallization on the filter and clogging of the filter cake. This results in increasing entrainment and reducing filter speed. A considerable amount of oil is entrained in the filter cake, which can be as much as 60-70% for milk fat. 

Solvent fractionation is the most efficient of all the fractionation processes. It is also the most expensive. The crystallizers used for solvent fractionation may be scraped-surface heat exchangers (SSHEs), such as the one shown schematically in Figure 21, with a typical commercial filter shown in Figure 22. The miscella of melted fat and solvent passes into the SSHE, where the high shear and temperature differential and relatively low viscosity encourage rapid crystallization. The mean residence time in the crystallizer is often on the order of 30 min, compared with up to 24 h for the Tirtiaux process. 

Figure 8.1. Example of a 3-step fractionation process for milk fat, with optional recycling of some fractions. AMF — Anhydrous milk fat DP = Dropping point of the fraction O — Olein or soft fraction of given step S = Stearin or hard fraction of given step (Gibon and Tirtiaux, personal communication).

Fig. 34.22. Fat fractions from cascade fractionation. (From Tirtiaux, A., in World Conference Proceedings, Edible Fats and Oils Processing Basic Principles and Modern Practices, D. E. Erickson (Ed.), pp. 136-141, AOCS, Champaign, IL, 1990. With permission.)...

The process for cholesterol removal from anhydrous milkfat was patented by General Mills (41). Fractionment Tirtiaux also disclosed the development of a vacuum steam distillation system called the LAN cylinder (38). The steam distillation process (Figure 2) was commercialized, producing a 90-95% cholesterol reduction in anhydrous milkfat with a 95% yield that was reconstituted into 2% fat fluid milk (42). The major disadvantage to the process is that it strips or removes most all volatile flavor components from the fat. These flavor components must be captured (i.e., vacreation) before the distillation process to attempt to reproduce the delicate flavors so desired for reconstitution into a butter product. 

Currently, dry fractionation of anhydrous milkfat is performed by two conventional systems—Tirtiaux and De Smet (both from Belgium)—which are bulk crystallization processes. The widely used Tirtiaux dry fractionation process enables one-step or up to hve-step fractionation of anhydrous butter oil at any temperature, ranging from 50°C to 2°C (37, 110-113). The milkfat fractions thus obtained can be used as such or the fractions can be blended in various proportions for use as ingredients in various food-fat formulations. The major shortcoming inherent in this system is the long residence time (8-12 h) for nucleation and crystal growth. 

V Gibon, A Tirtiaux. Winterisation, dewaxing, fractionation—Crystal clear. World Conference and Exhibition on Oilseed Processing and Utilization, Cancun, November 2000. 

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