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Growing of bulk starter cultures and grading it.
by Egon Skovmose on Tuesday, December 17, 2002
"Growing of bulk starter cultures and grading it".
Note: Growing a bulk starter cultures are for mainly large cheese manufactures but some smaller producers see advantages.
Any questions or comment please respond to egon@danlac.com
Your starter needs can be found in www.danlac.com/store
(Bulk cultures are market “B” were direct set is Visbyvac DIP).
The following overview shows how a starter can change with variations in temperature and inoculation amount:
22°C Less inoculation amount (app. 1/2 %)
More Lc. Lactis spp diacetylactis
Stronger red colouring by creatine test
Earlier and stronger CO² development
21°C More aroma
20°C
19°C Inoculation amount app. 1%
Red colouring by creatine test: 2 - 3
CO² development: relative early and medium
Aroma development: medium
18.5C
18°C Greater inoculation amount (app. 2%)
Fewer aroma bacteria,
especially fewer Lc. Lactis spp diacetylactis
Weaker red colouring by creatine test
Later and less CO² development
Less aroma
Fewer acid producers
The best balance between Lc. Lactis spp. diacetylactis, Ln. cremoris and acid developers are obtained with a growing temperature at 18 - 19° and an inoculation amount at 1 - 2%.
From our knowledge most cheese producer are using 21-22 °C (70 - 72 F) for their bulk starter, but this can very.
4. Grading of cheese starter culture
4.1 Organoleptic and visual grading
As taste is influenced by CO² content, grading should be done right after the first agitation, as part of the CO² will disappear during or after agitation. The starter should at this point, have a clean, acidic and aromatic taste. If it is too acidy, it has fermented too strong, while a slight off flavor often means that the fermentation is not quite finished.
The appearance of the curds before agitation can also give information
about the quality. They should appear shiny and firm without any
appreciable whey separation on top of the curd. On the other hand, a slight whey separation is one of the best criteria in showing that the starter has reached the right acidity. After agitation, the starter should have a smooth, viscous texture and must not be thick or contain lumps.
Research and experience has shown that the starter is best if the pH,
(measured 20 - 21 hours after inoculation), is between 4.55 and 4.60.
This depends on the culture used and on which media it is grown in.
C. Titration
Titration is an excellent supplement to pH. The acidity is given as ml of 0.1 NaOH per 100 ml milk (starter). (In a normal starter it is around 110 ml). There are some factors which influence the starter acidity. It is well known that CO² influences the acidity. If the starter is shaken strongly a great deal of the CO² will dissipate and the acidity will be lower. On the other hand if it is not shaken or if the NaOH solution is added quickly, the resulting acid will not be as low, which will give incorrect results.
Milk solids are also important. A high content of fat-free solids will give a higher acid. If skim milk powder is used to increase the solid content in the starter it will affect the acid, as added buffer would be present, which will give higher acidity.
D. Creatine Test
In deep, white porcelain dish 8 cm wide, 1-ml starter is added, 1 ml 40% NaOH and a small amount of creatine. This is mixed in the dish and the result is read in 30 minutes.
By grading the red colouring intensity, which spans from colorless to strong red, it can then be determined indirectly if there is a large or small amount of Lc. lactis spp diacetylactis in the starter.
As Lc. citrovorum is able to reduce the amount of diacetyl and acetoin, which are the ingredients that give colour reaction, the colour will be lighter with an increased content of these bacteria. In other words, we can get some colour reaction with a greater or lower amount of Lc. Lactis spp diacetylactis if the proportion between the two-aroma bacteria numbers is the same. One other irregularity is that the addition of manganese will result in no red colouring. It is these conditions which indicate that this test should be used with some caution.
E. Activity Test
Starter activity is the measurement of the number of bacteria and their viability in a given time period in acid development.
Add 1% starter to milk and incubate at 30°C for 6 hours, after which
titration and pH is measured. It is important to maintain it for 6 hours.
The 6-h activity test is very good in controlling acid activity.
Exactly 6 hours after inoculation measure the pH and acidity (titration) and at the same time do a creatine test. At this stage the pH is between 4.8 - 5.0 and a red colour results if there are many Lc. Lactis spp diacetylactis.
A starter with a lot of Lc. citrovorum can however be negative (minus red colouring) all the way down to pH 5.10 - 5.00.
Conclusion:
In practice the Creatine test and the activity test are the best criteria in selecting the starter.
Depending on culture and the media the above mentioned pH can deviate in a range of pH 4,6 - 5,1 where the best activity of a starter culture can be reached.
Please contact your culture supplier for information.
CHEESE MILK ACID DEVELOPMENT
by Egon Skovmose on Sunday, December 15, 2002
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.
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