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Problems with beer spoilage have occurred since the dawn of fermentation. Those problems have spurred many inventions, including stainless steel fermenters, addition of hops to retard lactic acid bacterial growth and the accidental invention of cold fermenting lager yeast that grow in conditions too cold for most spoilage organisms.

In leu of these technological improvements, most brewers have run into a case where “bottle bombs" or "gushers" form months after a thoroughly finished and dry beer has been bottled. Other times bottles go sour months after bottling. I’ve tasted kegs from breweries lately that have the distinctive horse blanket/sour from Brettanomyces in an IPA made with only Chico Saccharomyces yeast.


How does this happen? It’s contamination. Where does it come from? Since most modern fermentations are closed to air, the short answer is: dirty surfaces with living microbes or viable spores somewhere in the brewing process. Wort can be considered a wound up spring full of potential energy. There are many microbes other than brewers yeast ready and willing to unwind the energy to reproduce and spoil your beer! Contamination can have a devastating effect on cash flow.


Properly pitched yeast in combination with hops probably squashes most beer spoilage organisms due to rapid formation of alcohol and pH drop. But, even a few strong survive, they will raise their ugly heads later when they find their niche, and unfortunately may end up in customer’s hands (yikes). I’ve seen a trend where breweries are serving beer that didn’t make it and calling them sours. I’ve seen their books go sour as well. Only purposely inoculated sours should be served.

Keeping things clean 


Homebrewing is easy if all surfaces and the inside of hoses and pumps are cleaned with 180oF detergent with a high pH and physical scrubbing with brushes, and a sanitation step with an oxidizer like iodine or an acid detergent like Star San.


But, as homebrewers progress to professional brewing, homebrewers have a tendency to think that homebrew sanitation is sufficient for large brewing systems. Professional brewers use a technique call CIP or Clean In Place. This requires much more powerful chemicals to first lyse cell membranes on the surface of stainless and hoses using a spray ball and hydrostatic pressure recirculation in 180o F, 0.2% (0.05M)  to 2.0% (0.5M) sodium hydroxide or “caustic”. In this cleaning step, caustic causes fat component of membranes to be broken down into glycerol and free fatty acids. After a good recirculation cleaning step with caustic that includes every nook and cranny, no membranes should be intact on any surface. Every surface that comes in contact with wort cooler than boiling must be cleaned. Especially problematic are pump heads, heat exchanger plates and hoses where biofilms are formed. Even the hot side should be cleaned with a least caustic.

PBW and other detergents don’t have caustic to lyse membranes, and I am surprised how many professional brewers clean in place with a homebrew reagent.

Next, after the cleaning step with caustic, the equipment must be sanitized with an acid based oxidizer. This takes care of any spore formers that have rugged outer cell wall components that may be resistant to caustic. Oxidizers trash proteins and biomolecules, and cause cells to pop open. This reaction can be completed at room temperature. The best sanitizer according to most experts is peracetic acid or PAA. PAA breaks down into acetic acid after the peroxide is reduced by a target molecule such as a membrane or spore coat protein.  75 ppm (mg/L) PAA kills 100% of target organisms in 30 seconds. The low pH causes stainless to passivate and form the antimicrobial chromium oxide layer. Low pH also dissolves calcium deposits or "beer stone”.

Further, professional brewers can monitor the CIP regimen by swabbing surfaces and plating on petri plates. Beer should be assayed for microbial contamination to check for contamination. This subject will be cover in the next article.


Using these cleaning and sanitizing agents properly and performing qc assays on equipment and beer, the brewer can gain confidence that no other organisms are growing in product batch after batch.