pepperhead212 wrote:
One thing I found out recently on a bread baking forum was how the different sugars affect the different sourdough components - the wild yeasts and the lactobacilli - and that the fructose is what seems to feed the sour producing varieties of the lactobacilli. I figured this might explain Peter Reinhart's frequent use of agave syrup in his recipes, even though he never goes into detail about it. Either that, or he has stock in the companies. 
I think that reason for less than satisfying explanations of the feeding practices of wild yeast cultures is that they either are not fully understood or they vary so much that it is hard to generalize.
My understanding of a wild yeast culture is that it works and performs well because the yeast and lactobacillus organisms do not compete for food. One explanation I have read is that, unlike commercial yeast, the strain of yeast in most sourdough cultures lacks maltase-- leaving available maltose to the lactobacilli.
If this is true, the addition of a monosaccharide in the form of fructose from agave syrup would favor the yeast and give it a head start for gassing. Honey would perform the same function. Perhaps Agave Nectar was chosen so the bread remains vegan. That is the most common reason I make a switch from honey.