Using agar - how to increase accuracy of results?

[bio_overload]

Hi there,

I'm planning to do a biology experiment where I look at some yogurts with natural sugar and some with sweeteners to see whether the spoilage rates are roughly the same by studying the lactic acid production.

I plan to investigate this by counting the number of lactic acid bacteria colonies.

I've looked at a few methods and had a few questions. Why do some state that the experimenter should not "pour plates in direct sun light" ?

I've noticed that often, inconsistent sized colonies including pin point colonies form on the agar, I was wondering how I could reduce these to a minimum?

All advice is very much welcome!

Many thanks,

Liana

[Jorge1907]

Can you share the url for the methodology comment that concerns you? Some inhibitory dyes (e.g. rose bengal) can be photoactivated to the extent that they inhibit growth of target microbes.