Between 1930 and 1960 a number of continuous processes were developed. In the Alfa, Alfa-Laval, New Way, and Meleshin processes phase inversion takes place by cooling and mechanical treatment of the concentrated cream. In the Cherry-Burrel Gold'n Flow and Creamery Package processes, phase inversion takes place during or immediately after concentration, producing a liquid identical to melted butter, prior to cooling and working. The Alfa, Alfa-Laval, and New Way processes were unsuccessful commercially. The Meleshin process, however, was adopted successfully in the Republic of Russia. The Cherry-Burrel Gold'n Flow process appears to have been the more successful of the two American processes (29).
The Fritz continuous butter-making process, which is based on the same principles as traditional batch churn ing, is now the predominant process for butter manufacture in most butter-producing countries. In the churning process crystallization of milk fat is carried out in the cream, with phase inversion and milk fat concentration taking place during the churning and draining steps. However, because of the discovery that cream could be concentrated to a fat content equal to or greater than that of butter, methods have been sought for converting the concentrated or plastic cream directly into butter. Such methods would carry out the principal butter-making steps essentially in reverse order, with concentration of cream in a centrifugal separator, followed by a phase inversion, cooling, and crystallizing of the milk fat (37).
Increased demands on the keeping qualities of butter require that, in addition to careful construction, operation, and cleaning of the milk and cream processing equipment, research to develop machines that will ensure butter production and packing under conditions eliminating contamination and air admixture must be carried out. It has been demonstrated that butter produced under closed conditions has a better keeping quality than butter produced in open systems (38).
There are two classes of continuous processes in use: one using 40% cream, such as the Fritz process, and the other using 80% cream, such as the Cherry-Burrell Gold'n Flow. As much as 85% of the butter in France is made by the Fritz process. In this process 40% fat cream is churned as it passes through a cylindrical beater in a matter of seconds. The butter granules are fed through an auger where the buttermilk is drained and the product is squeeze dried to a low moisture content. It then passes through a second working stage where brine and water are injected to standardize the moisture and salt contents. As a result of the efficient draining of the buttermilk, this process is suitable for the addition of lactic acid bacteria cultures at this point. The process then becomes known as the NIZO method when the lactic starter is injected (Land O'Lakes, unpublished data, 1985). Advantages of the NIZO method over traditional culturing are improved flavor development; acid values as a result of lower pH; more flexible temperature treatment of the cream, because culturing and tempering often are accomplished concurrently; and, most important, sweet cream buttermilk is produced.
The latest in developments in butter making have been outlined in the European Dairy Magazine (39), with the article centering on dosing systems, and for the addition of salt and culture. In addition, a number of patents have been issued for improved butter-making processes (40), making butter directly from milk (41), and for flexible integration of added ingredients, and molding and demold-ing (42).
The Cherry-Burrell Gold'n Flow process is similar to margarine manufacture (43). The process starts with 18.3°C cream that is pumped through a high-speed destabilizing unit and then to a cream separator from which a 90% fat plastic cream is discharged. It is then vacuum pasteurized and held in agitated tanks to which color, flavor, salt, and milk are added. Then this 80% fat-water emulsion, which is maintained at 48.9°C, is cooled by use of scraped surface heat exchangers to 4.4°C. It then passes through a crystallizing tube, followed by a perforated plate that works the butter. Prior to chilling, 5% nitrogen gas is injected into the emulsion.
Although the Meleshin process continues to be in widespread use in the former USSR, the use of alternative continuous butter-making processes based on high-fat cream has declined in Western countries during the past 20 years (29). The principal reasons for this decline appear to be the economics and butter quality, particularly when compared with the Fritz process. A Fritz manufacturing process can be installed in existing batch churn factories with almost no modification to cream-handling or butter-packing equipment. The churns could be retained in case the Fritz breaks down. However, very little batch plant equipment could be reused in the alternative systems (ie, Gold'n Flow). When a completely new plant is being bought, the alternative systems still tend to be more expensive, and operational advantages over the Fritz are not significant. Butter from the Fritz process is nearly identical in its physical and flavor characteristics to batch-churned butter, whereas butter produced by the alternative processes tends to be different. These differences may be perceived as defects by the consumer, and manufacturers have been reluctant to alter a traditional product.
The alternative systems have a number of advantages compared with a modern Fritz line: (J) The most attractive advantage is the flexibility to produce a wide range of products with fat contents ranging from 30 to 95% butter-vegetable oil blends and the incorporation of fractionated fats; (2) these processes also present the possibility of a number of operational advantages by use of an efficient centrifuge during the cream concentration stage; fat losses in the buttermilk can be substantially reduced; and (3) the composition of the butter can be more accurately controlled, either by including a batch standardization step or by the use of accurate continuous metering systems.
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