Quality control: how to make sure your beers pass the mark

When you’re producing beer for sale to the public, you need to be a bit more careful than with your homebrew. Quality control and constant analysis are essential to understanding how your beer will behave over time, allowing you to refine your technique, improve consistency, and better judge the shelf life.

The benefits of this are clear: you can ensure your beer is shelf stable throughout its lifetime, and in doing so, gain the trust of your customers. Getting this wrong can leave a bad taste in your customer’s mouths, in more than one way. Trust in your brand will plummet, and it will take a long time to convince consumers to drink your beer again.

For the most part, small breweries don’t have the budget to accommodate a full lab to check for infections, defects, etc. However, there are several tests and procedures that can be carried out throughout the brewing process to ensure your beer is tasting and behaving how it should.


Sensory tests

Many small brewers rely solely on sensory tests. This simply means drawing a sample of the beer and analyzing it based on sight, smell, taste, and to some degree even sound and feel. Sensory tests can be carried out right from the mash through to the end of the expiry date. Here are some of the most common tests.

Brew day tests

You can ensure your beer is adhering to proper brewing procedures by carrying out a series of sensory tests throughout the brew day.

  • Mash conversion / iodine test: Not strictly a sensory test, but worth noting anyway. It’s used to check full conversion of starches to sugar after the mash. If the test fails, it’s worth double-checking the mash temperature, and leaving it a little longer. This can be paired with a gravity reading of the first runnings to be sure of conversion. Poor conversion can lead to defects in the finished beer, as well as a lower gravity than expected, and fermentation issues.
  • First runnings taste: It’s worth tasting the first runnings, which should be sweet and malty, though will differ depending on the grain bill. What you’re looking for here are signs of stale malt and foreign substances being introduced, such as iron from rusty equipment. If you detect a major problem at this point, it’s much cheaper to abandon the brew than if you had added hops, yeast, and kept it in the tank for a couple of weeks.
  • Yeast check: any brewer should be familiar with how healthy yeast smells, or more importantly, how unhealthy yeast smells. Before pitching, it’s essential to check that yours isn’t infected. This is particularly important when using wet yeast, which from time to time can suffer poor storage before it reaches you, leading to off flavours that will destroy an entire batch. With access to a fairly good microscope, you can also carry out yeast viability and vitality tests.

Post brew day tests

Once the beer is in the tank and fermenting, there are plenty of opportunities to carry out simple sensory tests to ensure all is going well.

Fermentation check

To check that fermentation is underway you can check the blow off tube or spunding valve. The liquid in the spunding valve or blow-off bucket should be bubbling once fermentation gets started. If pressure hasn’t started building, you can carefully look into your fermenter to check that a thick foam (or krausen) has started to form. Also, keep an eye on the temperature, which should be increasing as fermentation gets underway.

Diacetyl / VDK test

Diacetyl is created during healthy fermentation, and will generally fade by itself within a day or two after fermentation. However, in case of lagers and other cold fermented beers, you may need to increase the temperature to at least 15℃ for a couple of days to ensure it’s driven off. This test should be carried out before cold crashing, as it needs warm temperatures to break down.

Some people can detect VDK just by pulling a sample and smelling and tasting it — you’re looking for a buttery, popcorn type smell. The best way to be sure, however, is to draw a sample and heat it to around 30℃ — diacetyl is much easier to detect in warm beer. You can also then chill it back down, and compare it to a fresh sample that hasn’t been warmed up.

Taste tests

During fermentation, the yeast will throw out a wide variety of flavours and aromas, not all of them pleasant. As such, tasting for off flavours at this point is difficult. It’s best to wait until after fermentation. Even then, many off flavours will take several weeks to develop.

Detecting off-flavours

Learning how to detect off flavours is an on-going process. Some are easy to pick out and are very much in your face, while other, more subtle flavours are harder to pick out. The best way to get familiar with the most common beer defects is to partake in a guided off flavour tasting session. Alternatively, have a read through this piece that will help you become familiar with what to look out for, and what might be causing it:

Off flavors in beer: their causes & how to avoid them


Shelf life stability tests

The best way to see how shelf stable your beer is, is to carry out regular sensory tests under different circumstances. It’s worth pulling aside at least 10 bottles per batch to carry out quality control tests to determine the shelf life of your beer. Keep a number of your beers refrigerated under optimal conditions, ensuring you label them well and keep track of how long they’ve been in cold storage.

The rest of the beers can be tested at room temperature, or even better, in an incubator. At room temperature, it can take a long time to complete the tests. An incubator, on the other hand, will speed up the process considerably. This allows you to decide on a fairly accurate expiry date without guesswork, but it also shows you whether infections and off flavours are in your beer in a much shorter time.

Incubator tests

If you have access to an incubator, it’s ideal to keep the temperature at 30℃. You can build a budget-friendly incubator by converting an old fridge. In theory, one day of storage at 30℃ equates to one week of refrigerated storage. 

You can carry out daily tests to see how the beer changes over time. Be sure to make detailed notes, recording how the aroma, flavour, and appearance change day by day. In an ideal world, you’d test 2 or 3 bottles per day to check for consistency across the batch, though this isn’t always feasible on a small scale. 

If you start to taste off flavours and the beer begins to sour within a day or two at 30℃, your beer is badly infected. It’s advisable to carry out further tests at this point (see below), but be sure to test several bottles to ensure it’s not just one bad bottle.

If you’ve maintained high levels of hygiene throughout the brewing and packaging process, and have avoided introducing too much oxygen, your beer should last for many days at 30℃ without souring or developing other flaws and off flavours. It’s likely that flavours and aromas will fade (particularly hops) but the beer should remain palatable.

By checking daily, you will know at which point your beer begins to lose its flavour, and can set an accurate expiry or best before date. So, if your beer still tastes good after 20 days at 30℃, you can confidently assume that it will taste good after 20 weeks (around 4 months) in cold storage.

Detecting infections

Even with an incubator, it can sometimes take some time for bacterial infections and wild yeasts to become noticeable. You’ll need a very good microscope (and you’ll need to know what to look for) to accurately check for wild yeast and bacteria that shouldn’t be in your beer.

However, there are quicker, more affordable solutions. The following media from Siebel Institute Laboratory are two examples: 

  • LMDA Lee’s — Multi-Differential Agar — detects common brewery germs and spoilage microorganisms using media colour change to identify them.
  • HLP-Medium — Hsu’s Lactobacillus/Pediococcus Medium — detects both Lactobacillus and Pediococcus, the two most common brewery spoilage bacteria, without requiring lab equipment.

Dissolved oxygen

Once your beer has fermented, any contact with oxygen will drastically shorten its shelf life. Dissolved oxygen (DO) will stale your beer over time, speeding up the process of hops fading, malt staling, and the tell-tale cardboard taste and brown colour of an oxidized beer. DO can be reduced with proper packaging processes and equipment, as well as tank to tank transfer techniques.

Testing for DO requires expensive equipment, but can be an invaluable investment if you plan to sell your beer on a large scale, either nationally or internationally. But, even small scale sales can benefit from monitoring DO levels, especially if you can’t guarantee that your beer will be kept cold while in storage.

Dissolved oxygen equipment

You will need a DO meter that is capable of measuring in parts per billion, rather than million. Measurements should be taken whenever you move your beer from a fermenting tank to a bright beer tank, to ensure there’s no oxygen entering the beer during the transfer. It should also be measured immediately after packaging, which will require further equipment that can puncture the bottle cap or can lid.

Regular DO measurements allow you to detect where excess oxygen is entering your beer, enabling you to tackle the problem at the source, and thus increase the shelf life of your beer. However, the required tools will typically cost in excess of €10,000.


Taking notes

One of the best ways to maintain consistency is regular log keeping of the brewing, fermentation, packaging, and even cleaning processes. In-depth logs also allow you to backtrack more easily in case of problems, enabling you to see where you might have gone wrong.

Brew day logs

Every brew day it’s important to take notes of ingredient and water quantities, gravity readings, pH measurements, temperatures, transfer times, and even pump speeds. While this might seem excessive, it will help you replicate the next batch, and also let you know that you’re on target. By comparing the notes from previous brew days, you can see if the current readings and timings you’re getting are drastically different for some reason or other.

Notes that detail transfer times and time to boil, etc., are also a useful way to determine whether your equipment is working as efficiently as it should. If you notice that it takes longer and longer to reach a boil each brew day, it’s worth servicing your heating system, or checking for malfunctions. If transfer times seem to take longer, it could suggest filtration problems, or blockages.

Fermentation logs

Likewise, fermentation logs are a great way to monitor a number of factors:

  • How much pressure is built up naturally during fermentation?
  • How much did the pressure drop after cold crash? Is it consistent?
  • How much did this yeast strain attenuate and how quickly?
  • How much did the temperature rise during fermentation, and how much did it drop after?
  • How much yeast were you able to purge?
  • How did the beer taste at each stage? What did it look like? How long before it was ready to cold crash or package, etc.?

This allows you to quickly detect if something isn’t right during fermentation, as you can easily compare notes from the previous batches. It’s also a good way to compare different yeast strains and how they perform. Meanwhile, logging your dry hopping techniques will help you see what works for you.

Packaging logs

You should be recording all the beer that is packaged by law, but there are other elements that you can record to help yourself. If you do have DO equipment, take regular measurements across the process, and note them down, to compare with previous batches. 

Also, keep a log of how long it takes to package X amount of beer, as well as things like tank pressure, and any filling machine settings. This can help new team members set up the machine if you’re unable to attend a packaging day, but also helps you maintain consistency.

Cleaning logs

Cleaning is at least 80% of brewing, but it pays to keep records as to what has been done, especially if there are several people working in the brewery. The state of each piece of equipment should be recorded with the date clearly shown, e.g.

  • Brew kettle = caustic wash and rinse;
  • Heat exchange = caustic soak;
  • FV 1 = acid wash;
  • FV 2 = hot rinse, venting co2 — needs caustic wash, etc.

This prevents the same job being done twice, or not at all. Also, record details about the solutions in the CIP station tanks if you have them. If you have a vessel filled with peracetic acid, record the concentration, the day it was filled, and if it has been used for anything already. This prevents over use, wastage, or the solution staying too long.