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Cheese Manufacturing of Ultra filtrated Milk
by Egon Skovmose on Friday, October 24, 2003
Cheese Manufacturing of Ultra filtrated Milk:
In normal cheese process, milk coagulates by the addition of a rennet enzyme and by the curd being cut, stirred and eventually heated in order to have a desired amount of the whey removed. At the same time there is an acidification, which converts milk sugar to lactic acid, Ca+2 salts which are especially important for cheese consistency. By ultra filtration some of the water is removed, the milk sugar and most dissolved salts in the form of a permeate are collected before coagulation. In relation to the traditional cheese, ultra filtered cheese will contain too much milk sugar and lactic acid, so it becomes too acidic. At the same time a lesser part of the calcium will be removed because whey departure now has happened before lactic acid development. Further whey proteins will be transferred to the cheese and there will be difficulties in getting moisture content down.
When manufacturing cheese with the help of ultra filtration, the task is therefore to influence these conditions.
In manufacturing of "sour" cheese as, for example, Feta or Camembert a reduction in sugar content is not necessary, when these cheese types can be produced directly from concentrate (the retentate).
A reduction of the sugar content can be achieved by washing with water.
In the traditional manufacture of Danish and Dutch cheeses, this is accomplished by water addition either to cheese milk or to the whey during stirring.
The water in principle can be added to the milk before ultra filtration. This is very uneconomical in practice, because a relatively large amount of water is used, which then has to be removed by ultra filtration.
The amount of water, can, be diminished considerably by waiting to add the water, until a part of the permeate is removed. So in principle the more permeate, there is removed, the less water we have to use to obtain a certain dilution of the sugar.
In some cases after coagulation of the ultra filtrated milk further mechanical working is required to remove whey - a "washing out" of sugar by adding water to cheese curds.
Calcium content can also, be reduced by acidification. Some of the dissolved calcium is removed together with the permeate.
Such a pre-acidification can be carried out as a bacteriological acidification. It is difficult to obtain the right acidity before ultra filtration. The acidification will also continue during the process, if it is not stopped by pasteurization or a sufficiently high ultra filtration temperature.
It would be better to perform an acidification, for example, by addition of diluted lactic acid. Only a very light pre-ripening is required. The ultra filtrated cheese gets a mealy consistency, when the calcium content is brought down too far.
Moisture content can be changed by changing the degree of the ultra filtration process itself. This method is used for the soft and sour cheese such as, Camembert and Feta.
In most cases there is an acidification within the first 24 hours after ultra filtration and also during the acidification process whey removal, which helps to reduce moisture content. High salting, which occurs in the manufacture of Feta-cheese, helps to reduce the moisture content.
The question is therefore, how moisture content can be further reduced. One of the methods, which can be used, is a vacuum evaporation of the concentrate.
In Holland they have, for example, done some research with removing the last part of the moisture in a so called surface scraped evaporator and have in this way obtained fairly promising results.
An other method to increase solid content is to further treat the curd from the ultra filtrated milk by a modified cheese process.
It is a method, which is used to manufacturing of soft cheeses, for example, in Switzerland and in Germany.
The highest yield increase, results from concentrating as much as possible. By manufacture of normal molded UF-Feta, the milk is concentrated approximately 5 times. In feta, where the curd is cut into cubes, there is in reality a strongly modified cheese process with a certain whey expulsion. Less concentrating is used and so we get less yield.
Semi-hard or hard cheese, research has shown that it is best to concentrate approximately 2 times.
A higher degree of concentration has certain drawbacks. One of them is that, the curd very quickly becomes too solid, and becomes too difficult to cut, if it has to be done in a normal cheese vat. It is a problem, which some has tried to solve with the help of their Alcurd-coagulator. Other companies are working also at trying to find a solution to this problem.
One other drawback in working with a high concentration is that there are difficulties in getting the cheese curds to bind together.
It is obvious that 2 times a concentration does not give as large a yield, because a large part of the whey proteins are not transferred to the cheese.
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