How are you measuring water activity level?:cross:
Quote from FDA:
In simple terms, it's a measurement of "available" or "free" water in a food... i.e., available for use by microbes. It's one of the factors used to determine the risk potential of food spoilage (pathogenic microbial growth). Anything with a aW of less than .85, does not support the growth of pathogenic microbes.
Foods with a high concentration of sugar have a low aW. Jams, jellies, honey, sugar syrups, etc. fall into this category. So raw LME would too and it's probably so low that yeast growth isn't supported. But mix a little water in and heat it up and the aW will shoot up. It would take an insanely high specific gravity for an LME solution to have a aW too low for yeast.