Incubation temp i.e. 30°C or 37°C will depend on what organism you're interested in.
i.e. coliforms (30°C), E.coli (37°C). If you're interested in both organisms, then incubate at 37°C, just coli, then 30°C, and continue onto confirmation step according to the organism you're interested in after 24/48 hours.
The standard method for coliform/E.coli/bacterial test, pres/abs is, for Australia, AS 1766.2.3. Not too sure what the ISO standard number is. Tubes can be incubated at 30°C for up to 48 hours (E. coli 37°C). Tubes can checked at 24 hours and then if gas present in the Durham tube, onto confirmation step. If not then continue to incubate up to 48 hours and confirmation step where gas is present in the Durham tubes.
Presence of gas = presumptive coliforms. (typically 2/3 tubes with gas = presumptive +ve, 1/3 not considered to be presumptive. It's not always easy to see gas due to size of gas bubbles and turbidity of tubes. If time is not a factor then incubate to 48 hours and leave the 24 hour check - unless results need to be known sooner rather than later.
I agree yr initial comment. As you probably know there is a (ongoing) historical encyclopedia on the subject of "Coliforms". Started around 100 years ago.
To illustrate the reason for the (probably) infinite discussion here are 2 quotes from Compendium of Methods for Microbiological examination of Foods, 4th ed,2001 (there is, I think, a later edition but i anticipate that situation not significantly different) -
The coliform group is defined on the basis of biochemical reactions, not genetic relationships, and thus the term "coliforms" has no taxonomic validity. Coliforms are aerobic and facultatively anaerobic, gram negative, non-sporeforming rods that ferment lactose, forming acid and gas within 48 hours at 35 degC. An incubation temperature of 32 degC is usually used for dairy products.
"Coliforms" and "Faecal Coliforms," practically speaking, are those microorganisms that are detected by the "coliform test" and the "faecal coliform test," respectively.
Dairy not my area of expertise but the reason for the differences in incubation temperature are probably, primarily, that it optimizes "bacterial" growth. For example see -
(eg pg 3)
also can see this dairy article -
The general result is that Globally procedural variations do undoubtedly occur.
I have unfortunately no idea as to Slovenian Standard Procedures (if any) for the (unknown) product.
Regarding Australia, I have Coliform Standard AS 1766.2.3 - 1992 (latest ?) which has the following text -
Where the test is to estimate the level of coliforms only as an index of potential spoilage of the product and of hygiene, an incubation temperature of 30degC is specified. However, where the test is to be extended to include the estimation or detection of E.coli, incubation at 37degC is specified. Cultures which have been incubated initially at 30degC cannot be used for further tests for E.coli.
(I daresay the justification for this general use of 30degC is available somewhere (?) but so far I have only seen it (generally) applied in Australia. But it's a big World and this measurement as illustrated above is, in Principle, self-definable. I have personally had numerous data arguments with customers who used their own shortcut modifications rather than an official Procedure).
PS - afaik ISO used to use 37degC but currently appear to (ingeniously) sit on the fence, ie -
Microbiology of food and animal feeding stuffs — Horizontal method for the detection and enumeration of coliforms — Most probable number technique
Enumeration is carried out by calculation of the most probable number (MPN) after incubation in a liquid medium at 30 °C or 37 °C.
NOTE The temperature is subject to agreement between the parties concerned. In the case of milk and milk products, the temperature of incubation is 30 °C.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
bacteria which, at the specified temperature (i.e. 30 °C or 37 °C, as agreed) cause fermentation of lactose with the production of gas under the test conditions specified in this International Standard