MadSci Network: Microbiology

Re: what are the different stages of mold and how do they occur on cheeses?

Date: Sat Apr 22 13:39:10 2000
Posted By: Don Schaffner, Faculty, Food Science, Rutgers University
Area of science: Microbiology
ID: 955903839.Mi

> ... on the cheddar first there was white fuzz, then there were green
> spots which eventually turned black. could you please explain these 
> stages to us. 


First, keep in mind that even if you don't see anything going on, the 
molds may be growing. They are microscopic, so you won't see them until 
there are so many cells that they become *macro*scopic.

The "white fuzz" is made of mold hyphae. They are sort of like the "roots" 
of the mold. The green color is from the mold spores. Spores are like the 
seeds of the mold. Have you tried looking at any of these samples under 
the microscope? Molds can be very interesting and even beautiful under the 

I'm not sure what the black color is from. Molds don't usually change 
color with age, so the black color is either from a different species, or 
is just a really dark green color. Taking a look at both samples under the 
microscope miqht shed some light.

> Also the other two cheeses(romano and parmesan) did not get moldy but 
> they sweat a lot. 

These two cheeses have a lower "water activity". Water activity is not the 
same as water content, but is a measure of the available water in a food. 
Because these cheeses have less available water, molds grow slowly or not 
at all. Also, because of the low water activity, these cheeses tend to 
absorb water from the air... this is the sweating that you see.

Eventually, the water from the sweating may raise the water activity to 
the point where mold growth is possible.

Good luck with your experiments.

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