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Microbial Quality Control in the Brewery

What is Microbial Quality Control (MQC)?

Quality Control refers to how we monitor a process AND react to any problems identified in order to control quality. Microbiological Quality Control (MQC) in a brewery refers to testing for beer spoiling microbes AND reacting to any undesirable findings by removing the contaminant and taking measures to prevent a re-occurrence.

Why Do it?

Contaminated beer creates off flavors that can cost you $ and permanently damage your brand. Some contaminants can take up residence in the brewery and cause off flavors and profit losses for months or even years! This is known as “Harborage” and it is no joke when it happens to you and your business. MQC will help you detect problems sooner and trace their source so you can eliminate them.

Where to Sample 

Where you sample for contaminants is crucial for effective MQC. There are many places you can sample for contaminants in a brewery but if you are just starting out, begin by sampling at three key points in the process. You can add more sample points later depending on what you find and your particular needs. By sampling at the three critical control points below you can detect contaminants at a lower level and earlier in the process.  Just as important, sampling from these points allows you to quickly hone in on the source of the contamination–  knowing where the contaminant originated from allows you to remove the contaminant from your brewery more quickly and with less effort!

  1. The fermenter after wort transfer but before pitching yeast— By sampling the fermenter after it is full and before yeast is pitched you are accomplishing several things at once! Namely, you are identifying wort contaminants early in the process that may have originated from three of the most common sources–  the heat exchanger, transfer hose and the fermenter itself.  If this sample comes up positive you can immediately focus on cleaning and sanitizing the three above components.  Sometimes you may also need to change the SOP (Standard Operating Procedure) for cleaning and sanitizing these components to prevent a re-occurrence.   In some cases you will want to sample each of these components separately to pin down exactly which of the three was the source.  Sometimes it may be more than one of them.
  2. The yeast slurry— Yeast can become contaminated during harvesting and storage.   No matter how sanitary the wort, pitching contaminated yeast is a sure way to ruin good beer! Detecting contaminants in the yeast before pitching it can save you the expense and time of ruining an otherwise perfect wort.  Contaminated yeast slurry should be dumped.  It’s also a good idea to clean and sanitize the brink and collection hose.  You will likely want to check any beer fermented by the yeast for contamination.  There may still be time to stop distribution of kegs and packaged product.
  3. Finished Product— Sampling serving tanks, kegs, bottles, cans etc. serves as the final point in the process. By verifying finished product you help ensure that contamination didn’t enter the process downstream of fermentation.  For instance, undetectable amounts in the starting wort may grow to unacceptable levels during fermentation and after packaging.  Other common sources include contamination during bottling/canning or from bright tanks.

 Taking a Sample

1)  Label

Clearly label each sterile container you will use to collect samples with a sample name (i.e. Fermenter 1, Bright tank 6, lot#00743 etc.) and date. Use a sharpie or other permanent marker.

label

Label ALL samples before you start.

 

 2)  Wash your hands and put on clean latex gloves

Wash hands and forearms thoroughly in warm water and soap all the way up to the elbows. Dry off with a clean towel and put on latex gloves. You can spray alcohol or other sanitizer on the gloves after putting them on for an additional layer of protection.

Washing hands and forearms is one of the most important steps for sanitary sampling

Washing hands and forearms is one of the most important steps for sanitary sampling

 

 3)  Collect a sample (From a Tank)

First you need to sanitize the valve you will collect from. This can be done in a couple different ways depending on the type of valve (see below for two examples).

For a dedicated sampling valve: Fill valve with 70% alcohol and briefly flame to burn off the alcohol.

Use tubing to fill the valve completely with 70% alcohol

Use tubing to fill the valve completely with 70% alcohol

Flame the valve long enough to burn off the alcohol

Flame the valve long enough to burn off the alcohol

 

For a standard valve: Attach a 90 degree elbow to the valve so that it can be filled with sanitizer (i.e. PAA or similar). Let the valve soak for 5-10’ and then remove the elbow and attach a sanitized barb for sample collection.

Attach a clean 90 degree elbow to the valve

Attach a clean 90 degree elbow to the valve

Fill the elbow with sanitizer and let stand for 5' to 10'

Fill the elbow with sanitizer and let stand for 5′ to 10′

Sample Collection: This is the same for any valve type. Run off liquid for 5 seconds to flush sanitizer. Collect liquid in a sterile container by holding it 0.5 to 1” below the barb or valve without touching the tube or anything else. 20-50mls is typically enough.

Run off liquid to flush sanitizer.

Run off liquid to flush sanitizer.

carefully transfer liquid to the sample container without touching the valve/barb to anything.

carefully transfer liquid to the sample container without touching the valve/barb to anything.

 3)  Collect Sample (From Packaged Beer)

 Open bottle/can in a clean, dry location. Flame the lip of the container thoroughly. Pour off approximately ½ the beer to a waste container. Gently swirl the remaining beer to resuspend any settled yeast/microbes. Carefully pour 20-30 ml into a sample tube. Alternatively, you may use a sterile 10ml or 25ml pipette to transfer the beer.

thoroughly flame the lip of the container

thoroughly flame the lip of the container

Pour off 1/2 the beer and gently swirl to resuspend the remainder

Pour off 1/2 the beer and gently swirl to resuspend the remainder

Carefully pour the beer into a sterile container--  without touching the lip to the container or anything else.

Carefully pour the beer into a sterile container– without touching the lip to the container or anything else.

 3)  Collect Sample (From a Surface)

Sometimes it is important to sample a surface in the brewery.  This is usually accomplished by using a sterile swab that is cultured for 24-48hrs in an appropriate enrichment media for analysis.  Firmly swab over an area of 4 square inches.   Drop the swab into a sterile tube cotton side down without touching the swab tip or the lip of the tube.

hold the swab as far away from the cotton tip as possible while swabbing a surface

hold the swab as far away from the cotton tip as possible while swabbing a surface

Drop the swab into a sterile container holding it from as far away from the cotton tip as possible

Drop the swab into a sterile container holding it from as far away from the cotton tip as possible

 

  3)  Collect Sample (From a Yeast Slurry)

Sample yeast by re-suspending it as well as possible and then following the instructions above for sanitary collection from a valve. If you enumerate and assess yeast viability use the same sample for MQC and enumeration/viability testing. Often times the yeast slurry will be very foamy after re-suspension. Diluting  in sterile H2O will de-foam the sample.

 What to do With the Results

Now that you’ve collected your samples you need to analyze them for contaminants. Whether you send them off to a professional lab or analyze them yourself you will be faced with interpreting the results and reacting appropriately. Below are four common scenarios:

  1. “My fermenter sample and finished product were contaminated but the yeast slurry was clean”: You most likely had a contamination event at either the heat exchanger, transfer hose or the fermenter itself. You can now test each of these individually to trace the source and double check your cleaning/sanitizing process at each of these points to solve the problem. Heat exchangers may need to be disassembled to clean/sanitize, hoses may need replacement and/or you may need to change the way you sanitize the fermenter.
  2. “The Yeast slurry and finished product were contaminated but the fermenter sample was clean”: You most likely had a contaminated yeast slurry. Double check cleaning/sanitizing of the yeast harvest hose and storage containers. Don’t re-pitch the contaminated yeast!
  3. “The finished product was contaminated but the fermenter and yeast slurry were clean”: You most likely had a contamination event post fermentation (i.e. in a transfer hose, serving/bright tank, keg or bottling/canning line). You can now test each of these individually to trace the source and double check your cleaning/sanitizing at each of these points to solve the problem
  4. “The fermenter, Yeast slurry and finished product were contaminated”: You most likely have wide spread problems. The yeast may have been contaminated from a heat exchanger, transfer hose or fermenter in a previous brew and then re-pitched. You may also have problems in the packaging process. You should double check cleaning/sanitizing measures throughout the brewery and test each individual point to trace the source(s).