Structural changes by manufacture of ice-cream

In the majority of publications about manufacture of ice cream it is examined as complex multiphase system.

   What it means?

   I shall try to give you the answer to this question.

   The basic components of ice cream are water of which sugar and the stabilizer are completely dissolved. The dairy protein is in colloidal form in skim milk and fat as emulsion in cream. The largest structural change during manufacture of ice-cream occurs during freezing and temper, thus in weight are included air bubbles, and ice-cream turns to foam, and the most part of water will be transformed to fine ice crystals. Further fat, air and crystals of ice are in regular intervals distributed in the rest of water, which represents viscous high concentrated syrup from the dissolved sugar and the stabilizer.

   For reception of high-quality ice-cream are important not only separate components, but also all production. It begins with processing a mix before freezing and mentions except for it all conditions of freezing, temper and storages.

   Manufacture of ice-cream begins with preparation of a mix. If the mix prepares in pure conditions it renders rather small influence on quality and stability of ice-cream. This industrial stage will not be to be discussed in the given report further, I would like will stop at those industrial stages which render significant influence on quality of ice-cream.

   Homogenization of a mix for manufacture of ice-cream

   The mix for manufacture of ice-cream is exposed to homogenization proceeding from various reasons. First of all, particles of fat are crushed, that provides optimum process of freezing, and also a good consistence of an end product.

   Other function of homogenization consists in stabilization of border zones between water and fat. For these purposes dairy proteins are very well used. Especially, casein fractions of milk, which represent very flexible molecule, distributed generally of surfaces of fatty drops and covering them myceliar with a protein.

   Already for a long time it is known, that the temperature of 75-80 degrees is optimum for homogenization of a mix of ice cream. It was proved by that intermolecular forces in a molecule of casein at these temperatures are much weaker also than a molecule become more mobile.

   Emulgator, such as monohlycerides, play a functional role in time of homogenization mixes of ice-cream. Evidently it can be looked after in the pictures made with the help of a microscope on fig. 1 which displays a mix of ice-cream of 10 % of fat content, homogenated at 150 bars, And - without emulgator and - from 0,4 % a dosage monohlycerides. Finnier size of fatty balls and best their distribution on all mix of ice cream is reached at use emulgator. On the other hand, function of emulgator is a little bit limited, as monohlycerides at temperature of homogenization are in liquid form. In such form monohlycerides completely dissolved also can mix up with fats. Force of an attraction on a boundary surface between fat and water is very small, the same concerns also a superficial pressure. The own effect emulgator is shown only at cooling and maturing of a mix of ice cream that renders indirect influence on an opportunity of beating of a product.

   Cooling of a mix of ice-cream

   After homogenization and heat treatment the mix of ice cream is cooled up to temperature of maturing of 2-5 degrees with. If process of cooling occurs in lamellar warm-exchanger it occupies all some seconds.

   Examining process of cooling from the physical point of view, it is possible to allocate in it two basic functions. First, there is a process of crystallization of monohlycerides at decrease of temperature to 40 degrees. In crystallical form monohlycerides it is weak dissolved in liquid fats and are inclined to sedimentation. This process causes the raised ability monohlycerides to draw water. These two changes result to that monohlycerides accumulate in a boundary phase more actively, than earlier.

   During last stage of cooling up to 2-5 degrees crystallical layer of monohlycerides is on a boundary surface. Process of crystallization of fats, amplified already by crystallical monohlycerides at the same time begins.

   Maturing of a mix of ice-cream

   There was a long-term tradition and practice of endurance of a mix of ice cream during night at temperature of 2-5 degrees. This so-called maturing is a necessary condition of good freezing in freezer and provides a cream consistence of ice cream.

   Earlier recognized that maturing it is necessary for maintenance of enough of crystals of fat in a mix of ice cream before process of freezing. As a result of new researches for last 10 years came to opinion that many physical processes during maturing proceed in particles of fat and in membranes of fatty balls.

   As far as today it is known, maturing is based on the following principles: monohlycerides, basically, form more or less crystallical a monomolecular layer around of fatty balls. Fat in the center of a fatty ball are crystallizing, these crystals however settle down definitely and there is a transformation of crystals, should pass some hours while process of crystallization will not achieve final result.

   Presence of monohlycerides accelerates process of crystallization of fats, monohlycerides provide also increase of the contents of firm fats in a fatty ball.

   Earlier believed, that the fatty ball is under construction of several layers, i.e. the external layer consists of fusible fraction, average - from middle-fuse fractions and the middle is in a liquid phase. However the liquid phase is absorbed on crystals is impossible to examine this fact as immutable as during process crystallization up to 90 % of fat hardens and by that that fact is necessary to accept that.

   As it was told above, the boundary surface between water and fat consists at once after homogenization of molecules of case in which are connected with mycelium dairy fiber. In a stage of maturing on a boundary surface is monomolecular crystallical layer. In this form monohlycerides render strong influence on a superficial tension that means, that they replace fibers on a boundary surface.

   This replacement of fiber represents process, which some hours last, on Barfeld it can be 24 hours. It has found out, that 85-90 % of an initial protein layer desorbtion from a boundary surface. In a mix of ice cream without monohlycerides after maturing twice more protein remains on a surface of fatty balls.

   Desorbtion of proteins from membranes provides water-repellent property of fatty balls that affects their agglomeration, and stability air bubbles rises.

   With the help of electronic microscope Buhgeim in 1992 has proved (fig. 2), that in ice cream with monohlycerides after maturing practically it is not observed a protein on a boundary surface, in comparison with a mix for ice cream at once after homogenization. Table 1 and fig. 3 display this phenomenon observably during manufacture of ice cream.

   Freezing of a mix of ice-cream

   After a mix it obtains has passed through freezer, typical structure of ice cream. In freezer crystals of ice are formed, they include air and the foamy structure, which is stabilized due to fatty drops, is formed.

   All process has a complex nature, and is necessary to create an excellent consistence, a good structure and cream taste, and also good stability at storage.

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