"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.