Post-boil wort contamination and why pre-boil water treatment matters

By Brian Grochowski – Aquionics Regional Sales Manager (Americas)

With the rapid expansion of new craft breweries across the country, it’s not surprising to see many of them take a ‘minimalist’ approach to water treatment in order to keep initial capital costs down.

Most new breweries are connecting to a municipal water supply system where the water has been chlorinated.  They then remove the chlorine with of GAC (granular activated carbon).  Some will make a few water chemistry adjustments, while others simply take the dechlorinated water and begin extracting the sugars from the grains through the mashing process.

Given that the incoming water is chlorinated and that the wort is boiled, many brewers make the false assumption that microbial contamination is not an issue immediately after boiling the wort.  Although it’s true that properly chlorinated water should not contain elevated amounts of microbial contaminants, it’s been well documented that some organisms are resistant to chlorine.  These chlorine-resistant organisms can multiply when exposed to favorable conditions and a food source.

Unfortunately, GAC can provide that harborage which results in downstream contamination, as we’ve discussed in previous articles.

Thermophiles can also survive the boiling process.  With no disinfection technology or treatment after GAC and before the mash, thermophiles and some chlorine-resistant organisms can cause wort contamination.  An old article published by The Institute of Brewing provides more details about common Enterobacteriaceae that have been documented in the wort.  Below are some notes on their findings:

• Citrobacter, Enterobacter and Klebsiella are some of the common Enterobacteriaceae found in wort.
• Enterobacteriaceae can slow the fermentation process and raise the pH.
• If not addressed, this type of contamination results in inconsistencies in beer taste and flavor profiles, especially with regards to fusel alcohols, esters, sulfur compounds, carbonyl compounds and volatile phenols.

An article titled The Microbiology of Malting and Brewing expands on this even further by noting the following key issues:

• Bacillus and Clostridium may be in the mash or wort which could cause excessive acidification, nitrosamine formation, or contribute to the production of butyric acid.
• Addressing contamination issues prior to mashing can improve filterability and extraction efficiency.
• Commonly found microorganisms at various points in the brewing process can be found below

Given the above issues, and the importance of quality and consistency in the final product, many breweries have used UV disinfection systems after GAC beds to counteract microbial contaminants like chlorine-resistant organisms, thermophiles and other unwanted organisms that colonize within the GAC beds.

Since many of these microbial contaminants can result in fairly specific taste and odor issues, simple organoleptic testing and experience may be enough to identify what specific contaminants may be causing quality and consistency problems.Once identified, UV systems can be designed specifically to provide the UV dose required to mitigate the risk of contamination of those organisms in the water used in the mashing process.

For more information on microbial contaminants found in the mash, wort and post-boil, please review the information in the links below.

https://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1974.tb03629.x/abstract
https://mmbr.asm.org/content/77/2/157.full