3. Emulsification and Processing
The margarine emulsion contains a dispersion of finely dispersed aqueous droplets within a crystalised fat lattice. The margarine manufacturing process consists of five unit procedures: emulsification, cooling, working, resting and packaging.
An emulsion is a suspension of one liquid in a second immiscible liquid. The margarine emulsion may be formed by batching of ingredients in appropriate proportion. Molten oil blended to requirement is mesured into an agitated tank. Oil-soluble ingredients including lecithins, monoglyceride surfactants, oil soluble flavourants, oil soluble vitamins and colourant are added to the molten oil.
Pasteurized aqueous phases are typically prepared from milk, water, salt, water soluble flavourants and preservative. The aqueous phase is maintained at 5 -10ºC after pasteurization and before mixing with the oil phase. Addition of a cold aqueous phase to a warm oil phase is accomplished with continuous agitation to form a coarse, but very unstable emulsion. An alternative process is continuous blending of oil phase and aqueous phase using proportioning pumps or other metering devices.
The mixed oil and aqueous phases are pumped to a tube chiller or swept-surface heat exchanger. The tube chiller is generally a cylinder that is cooled externally and that contains a centre shaft to which are attached scraper blades. As the centre shaft is rotated, the scraper blades remove product from the interior anular surface of the heat exchanger. The liquid emulsion is pumped through the heat exchanger/chiller, resulting in super cooling of the fat by a temperature drop from about 40 - 46ºC to 7 -10ºC. Crystallization begins with cooling and continues for 24 hours or more. Crystal development increases the temperature of the margarine emulsion several degrees as heat of crystallization is released. Post-chilling working by a rotor-stator texturizer influences the texture of the product. Generally, tub margarines are mechanically worked to allow crystal growth while preventing formation of a firm crystal lattice. As working increases, product consistency softens.
Stick margarines, however, are generally allowed to rest briefly post-chilling and before packaging to allow firming of product to withstand the extrusion forces of stick making. Whipped margarines are produced by injection of nitrogen into the liquid emulsion for either tub or stick form.
The working and/or resting steps are used to obtain optimal packaging consistency as well as for optimization of performance characteristic. Packaging of tub margarine is generally accomplished by automatic filling into tubs. Stick margarine is produced by extrusion of chilled product into forming moulds with subsequent wrapping of moulded sticks. Margarines are generally refrigerated for maintenance of physical structure and flavour and to prevent spoilage by action of microorganisms.Margarine analogs have proliferated in recent years. Products similar to margarine but not conforming to requirements set forth in the appropriate legislation are normally termed spreads.