P-41 - Mash Impact on Malt Microflora Survival in Unboiled Wort

  Some whisky distillers are concerned with the microbial loading on the incoming raw materials that are incorporated in their mash. This is due to the lack of the boil “kill-step” between mashing and fermentation. It is well established that other microbes besides the selected yeast strain impact fermentation in ways that can change distillate. Some distillers may want the “funky” aromas produced by bacteria like lactic acid and acetic acid bacteria. Others may be concerned with maximizing alcohol yields and enforce bacterial count specifications for their barley malt. It is up to the distillery to decide what is an acceptable practice for their desired spirit and operational performance but the traditional mindset of “what is on the grain is in the fermenter” may not be so clear cut. Recent work at the Rahr Technical Center afforded insight into the survival of bacterial populations from the malt during the mashing process..While working to understand the differences between aroma compounds produced during distillation by low and high bacterial loaded malts we found that contrary to industry expectations, mashing eliminates much of the malt derived microbial loading, even with malt at levels 200 times higher than typical distillers malt specifications.
To further study this phenomenon, bourbon mashes were inoculated with Lactiplantibacillus plantarum. Samples were collected at the start and at fifteen-minute intervals during the mashing process and subsequently plated to obtain the bacterial survival rates. The results of this work will provide distillers guidance for incoming barley malt and understanding where bacterial populations arise within their whiskey fermentations.