I dont mean to disagree RM, but I would sooner put a couple tbsp of table sugar in the jar than agave. Certain strains of lactobacillus will not readily ferment fructose, but most will do sucrose. High fructose agave is like 80% fructose, so there will be other saccharides in there, and you may very well get a strain that ferments it fine, but I have and would use sucrose, or even better, maltose. Now when it comes to sweetening a sauce I use agave, and the lighter in color the better, since it doesnt impart much of its own flavor.