5. CHEESE MILK ACID DEVELOPMENT:
5.1. FAST ACIDIFICATION:
This has been and is the most commonly used form for systematic acid development. It happens in practice either by adding bulk starter culture before the rennet in an amount of 0.5 - 1¼ % of cheese milk or direct set culture. Many plants add the starter at the same time, the vat has been started to be filled by milk. In the latter a longer acid development, normally 15 - 60 minutes is achieved. The amount of starter should naturally be regulated in relation to acid development time. The essential difference between these two procedures is that if the same inoculation percentage is used, a considerably larger number of bacteria in the milk will be present, because of the longer acid development time. The bacteria in a ripened starter culture are more or less inhibited. Such a culture requires, therefore, a certain time to reactivate. By adding the starter culture just before rennet addition, the acid production does not get going properly, at the beginning of the cheese making and the cheese may become too sour. To avoid this, make the acid weaker, but then the risk is increased for the harmful bacteria to develop and be a danger to cheese quality. Normally the lactic acid bacteria will develop and the production of lactic acid will prohibit unwanted bacteria growth. The bacteria, we normally use, require from 1 - 3 hours acclimatizing to new conditions, if they are being transferred from a ripened starter culture. An uneven course of acid development process will lead to a corresponding uncertainty in the cheese make. As far as cultures are concerned, these can have strong varying activity, because of different acid degree and age, different storing time and temperature and so on.
The best would of course be that the culture was in full activity the moment it was added to the milk, so that we avoided "the lag phase". We can for example before use, mix the amount of culture, we shall use for the cheese vat, with a corresponding amount of suitable tempered milk (25 - 30°C) and let the mixture sit, until we note certain activity (determined for example by titration or pH).
The mixture is then added to the cheese milk, which is given proper time for acid-development. Even with the transfer to the cheese milk, it also will mean a certain environmental change for the bacteria. The best though would be if the starter culture as soon as it is finished in the morning is cooled to less than 8°C.
5.2 SLOW ACID:
The idea behind this method is fermentation at a controlled reduced rate. The culture, which is used by fast acidification, is added to the cheese milk at a relative high temperature, (28 - 32°C) and is normally a ripened culture. This means the bacteria in the culture have stopped their acid production. The reason for this slow acid development is, that we add starter to pasteurized milk the day before, at a temperature of 5 - 10°C. The bacteria are, therefore, in full activity, when the milk comes into the cheese vat. 0.5 - 1.0% starter is added, and fermentation time is 15 - 20 hours. This method gives a smoother acid development under cheese making and pressing. By the use of ripened starter cultures, is normal by fast acidification, there will always be a certain time, before bacteria begin to multiply in cheese milk, especially in cases, where culture has been coagulated at longer time and is stored at a high temperature. Several, have done research with the method (slow acidification), but the results are varied.
Swedish research with Swedish cheese confirms that acid development during cheese making went somehow slower, but the cheese had considerable higher moisture content then by the fast method, and the quality did not improve. A Danish dairy company has however used this method with good results in several of their plants.
The slow method is without doubt more labour demanding than the fast method, because it requires greater care. Considering the fundamental importance acid development has in cheese milk it can be stated, that any attempt of making it more secure and stable will be worth the effort.
5.2.1 Control with Slow Acidification:
The milk is titrated and pH is measured at starter culture addition and again next morning. The acid should have increased .5 - 1.0 and pH have fallen 0.1 - 0.3 units. It is important, that we do this control daily, so that we have complete control with the acid development.
5.3 INOCULATION AMOUNT:
An increase in inoculation rate will result in an earlier corresponding pH decrease in relation to coagulation, and that the cheese end-pH becomes lower. A doubling of inoculation rate will lower pH and lower the cheese calcium content. An over excessive increase of inoculation rate can, therefore, lead to the stored cheese getting split, sour and "short".
An increase in inoculation rate lowers the cheese milk's pH because of the direct addition of lactic acid, but also because there are more lactic acid bacteria. This results in a faster fermentation in the cheese vat so the whey, which drains from the cheese curd during cheese making, is sourer. This whey will have dissolved more of the calcium, which is bound to casein. With the calcium also some of the phosphate is removed, which normally acts as a buffer in the cheese. When calcium is removed, the cheese consistency becomes "short" and when the phosphate is removed the cheese becomes sourer.
The cheese acid can be regulated considerably by changing the amount of inoculants, but it would normally not be recommended to change this more than 0.25% as too high inoculation can give spit, sour, "short" and brittle cheese. However, the inoculation can also be too little, and by normal production technique for semi-hard cheese 0.3 - 0.4% can be considered to be minimum, the cheese otherwise has a tendency to get unclean and tough. The stronger acid, which follows higher inoculants, will improve whey-drainage, which results in a lower moisture content in the cheese.