MadSci Network: Microbiology

Re: What is the diameter of mold (that grows on cheese)?

Date: Mon Feb 25 15:41:12 2002
Posted By: Charlene Wolf-Hall, Faculty, Food Science
Area of science: Microbiology
ID: 1014254609.Mi

Hi Carmen,

I am not sure I fully understand your question, but here is the answer that I have for you anyway.

The most common genus of mold that is responsible for spoilage of cheeses is Penicillium. There are also species and strains within this genus that are purposely added to cheeses - ever have blue cheese or Camembert cheese? Other mold genera can be spoilage problems in cheeses too, but for this discussion, I will focus on Penicillium.

The spores, or conidia of Penicillium species are round to oval shaped and range in diameter size from about 3 to 4 um. An excellent reference book that you may want to get through your library is Introduction to Food- and Airborne Fungi, Sixth Edition, Edited by R.A. Samson, E.S. Hoekstra, J.C. Frisvad and O. Filtenborg, 2000, published by Centraalbureau voor Schimmelcultures - Utrect, the Netherlands, ISBN 90-70351-42-0.

You can do a single spore inoculation by suspending spores in a diluent (you can use sterile water), diluting them further and then pouring the diluted solution onto growth medium. The excess diluent is poured off, and in theory, single spores will have been deposited onto the surface of the growth medium far enough away from each other to result in isolated colonies. I suppose you could use the surface of a cheese as your growth medium, but use a very diluted spore suspension or you will get a lawn of growth rather than distinct single colonies. If you do not have access to mold cultures, purchase some blue cheese and dilute a portion of the "blue" part of the cheese, which should be full of mold spores.

You can measure the diameter of your mold colonies over time (I would suggest measuring every day for 1 week) to get your growth data. You probably won't be able to see growth with the naked eye for about 48 hours after inoculation, depending on incubation conditions. The warmer you incubate, the faster they should grow, unless you get them too hot. Growth rate will vary depending on strain of mold tested, growth substrate (type of cheese), if there are any preservatives such as sorbates in the cheese, temperature, humidity and light may even have some effect. I had a question once about whether music would affect the growth rate - I never did hear back on that one.

I hope this has helped you with your experiment. Good luck.

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