NOTE! There is usually a lag period prior to microbial growth. This is not factored in this calculator. Doubling time is also known as generation time. Ensure that holding time and generation or doubling time use the same time units. I will add a tutorial to discuss the mathematics and applications in due course One of the applications that I will look at is the growth of Clostridium perfrigens during the cooling of meat. Spores of Cl. perfringens can be activated by heating. Most cases of food borne poisoning by Cl. perfrigens have been caused by heat activated spores that go on to germinate and produce toxin. The regulatory authorities in most countries prescrible cooling regimes for high risk products e.g. The Food Standards Code (FSANZ 2011) requires that “A food business must, when cooling cooked potentially hazardous food, cool the food:

a) within two hours—from 60°C to 21°C, and
b) within a further four hours—from 21°C to 5°C.

I will try to explain why this is important using the doubling time of Cl perfringens.