Re: At what point does sugar begin to retard mold growth?

I can't say that there is an absolute level of sugar which retards mold 
growth. It depends on a variety of factors. The method by which sugar 
inhibits mold or any other microorganism's growth is through the lowering 
of water activity. The sugar molecules bind up the free water molecules 
making them unusable to the organism to continue its life processes. 
Molds, are by far, the hardiest of the microorganisms with respect to 
ability to withstand low water activity (Aw) or "drying out." For your 
experiment, I would work in increments of 2% sugar solutions starting from 
0% and going to 8%. I think this gradient would clearly show the effects 
of sugar concentration on mold growth. Incidentally, the same holds true 
for salt, although salt is a little more effective in binding water. Just 
to warn you, there is an exception to every rule. There are some 
microorganisms which are resistant to high solute concentrations i.e. 
osmophiles which will thrive in the conditions mentioned above. Good luck 
and for more info, try: www.asmusa.org.