Miscellaneous Quality Control Procedures, from Low-Tech to High


The Microbrewery Laboratory Manual

by Fal Allen and Jason Parker (Brewing Techniques)

Many microbreweries are moving to a capacity that no longer qualifies them as microbrewers (whatever the current qualification of microbrewery may be). They have become regional breweries. At that size they can hardly even be considered “hand-crafted,” unless the brewer is very unlucky indeed.

Big is not necessarily bad — some of my best friends are regional brewers — but the bigger you become, the more costly mistakes can be, the larger you get, the wider your distribution and the longer your beer is going to be out in the marketplace.

Is your beer stable enough to take it? Is your beer consistent? How will you be able to tell?

Regional and megabreweries have available to them much more advanced equipment and laboratory techniques than do smaller breweries. As microbreweries grow larger they too will need to adopt more of these advanced procedures and the accompanying equipment.

In this, the final installment of the microbrewery laboratory manual series, we discuss advanced laboratory equipment and techniques.


Concept: Building a beer library won’t be as costly as many of the things talked about in this article, but it can be as useful. A beer library consists of packaged beers that have been pulled from the packaging line at random during the course of a run. They are put away for later evaluation.

It is important to know how your beer tastes right off the line and what it will taste like out in the market under different conditions. Simply buying a bottle of beer off of the shelf will not give you enough information. You won’t know how that beer has been treated. Was it kept cold the entire time? (Unlikely.) Was it left out on a loading dock in the sun? Did it travel many miles over bumpy roads? You won’t know, but a beer library will allow you to subject bottles of beer to specific environmental conditions and then analyze them.

The Range of Storage Conditions for a Beer Library

Store samples of packaged beer under the following conditions:


  • kept in the dark
  • exposed to light

Ambient temperature

  • kept in the dark
  • exposed to light

Warm (>80 °F/26 °C)

  • kept in the dark
  • exposed to light

You can pull packaged beer on a daily, weekly, or monthly basis or by batch number (every batch, every other batch). You will need to decide what works best for you and your brewery operation. At Pike Place Brewery’s Seattle operation, we pull samples twice a month because our turnover is very rapid, our market area is small, and we are self-distributed. At our contract breweries we pull samples from every batch, because we have less contact during the brewing process and less control over the remote distribution.

The samples in a beer library enable you to keep better track of your product and how it may be fairing out in the marketplace.

Procedure: First, determine how many bottles (packages or kegs) you will need to pull each time. This will depend on the number of tests you plan to run (6–24 bottles is common). Then you will need to store these bottles under various conditions for varying lengths of time (see box).

The incubator: An incubator will allow you to keep beer and/or lab samples at specific temperatures for specific lengths of time. (It will also enable you to control fermentation temperatures on test or homebrew batches of beer.) An incubator can be expensive if purchased from a scientific supply shop, but you can easily build your own.

First you need to find or build a box made of any durable material. You could even use a spare closet or cupboard (or an old, broken refrigerator). Insulate the box so that it retains heat. Purchase a thermostat with a remote probe set to operate in the heating range you want (50–110 °F/10–45 °C). Find a heat source and connect it to your thermostat. Put the remote probe and the heat source inside the box and the thermostat control outside. You are ready to incubate.

The heat source can range from a simple light bulb (for a small lab incubator) to something slightly more complex like a heater or a blow dryer for hair (for a closet-sized incubator). A blow dryer in a small cupboard works very well and is cheap and easy to rig up. Be careful to ensure that the heat source is safe and will not cause a fire or overheat your samples. Remember that if you use a light bulb for a heat source, it will make the beer become light-struck. You can shield the beer from the light in any of a number of ways.

Analysis: When analyzing your beer, consider the following three categories:

  • Taste. Does the beer’s flavor change over time? If so, how does it change and what causes those changes?
  • Biological stability. Is anything growing in the beer that should not be there (1,2)?
  • Physical stability. Does the beer fall apart over time? Does it develop haze (the result of precipitated haze)? Does it throw sediment? Does it oxidize?


Carbon dioxide testing devices: Carbon dioxide not only makes beer effervescent, it plays an important part in the beer’s overall taste. It influences the mouthfeel, the body, and the flavor perception. To make a consistent-tasting product, one must have consistent carbonation levels (measured in volumes) in the beer. This consistency is important both before and after packaging; it is normal to lose ~0.2 volumes of carbon dioxide during the bottling operation, and 0.05 volumes during kegging.

Consistent carbonation levels can be accomplished by knowing the temperature and the head pressure of an isolated tank — assuming the beer has had enough time to absorb the maximum amount of carbon dioxide at that temperature and is now at an equilibrium with the headspace. It is important to remember that the amount of gas a liquid can hold is directly related to temperature. A tank at 40 °F (4.5 °C) and 13 psi, for example, will have 2.5 volumes of carbon dioxide dissolved in the beer. That level is about optimum for most British-style microbrewed beers. (Detailed charts showing the solubility of carbon dioxide in beer at specific temperatures and pressures have been published elsewhere).

This method of determining carbon dioxide volumes, however, is rather crude and often unreliable. If your pressures gauge is off by 0.5 lb at a temperature of 32 °F (0 °C), the total dissolved carbon dioxide will be misrepresented by 0.05 volumes. The warmer your beer, the greater the variance, so you can see how inaccurate this method of determining consistent carbon dioxide volumes can be.

Testing Protocol for Beer Library Samples

Perform the following tests at 0–5 days, 30 days, 60 days, 90 days, and 120 days (optional):

Biological tests

  • bacteria count
  • wild yeast count
  • your yeast count

Physical test

  • color
  • bitterness units
  • haze fermentation
  • sedimentation
  • level of oxidation

Several devices on the market are made for more accurate determination of carbon dioxide levels in beer. The most common and widely used is from the Zahm & Nagel Company (Buffalo, New York). The Zahm-Hartung CO2 meter and the Zahm SS-60 are used to check beer storage tanks. The company also makes a device to check carbon dioxide levels in bottles and cans. These instruments, when calibrated and properly used, will force the beer sample into equilibrium and will therefore provide a much higher degree of accuracy. Zahm & Nagel also produce devices that enable you to adjust carbon dioxide levels in storage tanks (carbonating stones) and on the way to filling machines (in-line carbonation systems). These devices allow carbonation to be adjusted quickly if the need arises. They enable you to achieve a higher degree of consistency in your packaged products. Zahm & Nagel also produce several devices for checking the air content of bottled and canned products.

Package air and dissolved oxygen: Oxygen introduced into the beer after fermentation and during packaging has long been known to lead to staling and haze (4). Volatile, long-chain, unsaturated carbonyls such as the aldehyde trans-2-nonenal, with its characteristic cardboard-like or papery flavor, are formed or released during the storage of packaged beer when molecular oxygen is present. Measurements of molecular oxygen levels in the final packaged product therefore greatly assist brewers in determining the shelf-life of their beer.

However, molecular oxygen mixed with the gases present in the headspace of bottles or kegs is not the only cause of staling. Wort-derived components that are oxidized before the boil or by the movement of hot wort are also known to be responsible for beer staling.

To determine where oxygen is being picked up, take measurements throughout the beer-production process, including wort production, fermentation, conditioning, and packaging. Unfortunately for microbrewers, these measurements require two instruments — one to measure the molecular oxygen present in headspace gas, and another to measure dissolved oxygen in liquid solutions.

Total package oxygen (dissolved oxygen plus headspace oxygen) is usually calculated by measuring total package air using a piercing and shake-out device such as that made by Zahm and Nagel. This instrument allows the brewer to sample beer from a bottle, can, or pressurized vessel (the latter requires a special collection device). The instrument pierces the bottle crown (or can bottom), the entire apparatus is shaken, and the escaping headspace gases are directed into a burette containing a 15–20% sodium hydroxide solution. Carbon dioxide dissolves into the sodium hydroxide to form sodium bicarbonate, and all other headspace gases rise through the caustic into the scaled area of the burette, where they are measured in units of millimeters. The insoluble gases are collectively referred to as air.

With today’s technology, target bottle air levels should be no greater than 0.7 mL/12 oz bottle; between 0.2 and 0.5 mL is ideal. Oxygen present in a bottle’s headspace is often the result of incomplete carbon dioxide–purging of the filler and the filler bowl before the bottling run or in the filled bottle headspace.

Just as important to beer flavor stability as bottle air levels is the amount of oxygen introduced during mashing and brewing. Oxidation (losing electrons) and reduction (gaining electrons), collectively referred to as redox reactions, occur continuously throughout these stages. When oxygen is introduced during the mash or boil, polyphenols, melanoidins, and reductones — compounds that can act as antioxidants — will become oxidized. During fermentation, these reactions are minimized because of the strong reducing power of yeast. Once the yeast settles out or is removed by filtering, however, the oxidized melanoidins will likely take part in the oxidation of higher alcohols to form volatile staling aldehydes. Note that at this stage the beer will oxidize even without the presence of molecular oxygen (from the headspace). Therefore, it is very important to keep the wort in a reduced state during the mash and boil, which means keeping oxygen out of it.

The fastest way to tell if oxygen is being picked up during the mash or boil is to measure the dissolved oxygen present during these processes using a dissolved oxygen meter.

In the polarographic dissolved oxygen sensor, oxygen diffuses into an electrode through a thin polyethylene membrane. A constant potential is applied across the electrode, and the current flow — directly proportional to the concentration of dissolved oxygen — is measured. To help you locate sources of oxygen pickup, take dissolved oxygen measurements at several points during brewhouse operations, including the following:

  • recirculation of wort in the lauter tun
  • transfer of wort from the lauter tun to the kettle
  • wort in the kettle after the boil but before transfer to the heat exchanger
  • alcohol-adjustment water added before wort chilling
  • wort just before it enters the heat exchanger.

After fermentation, many more opportunities present themselves for oxygen pickup. Some areas requiring monitoring include the following:

  • beer transfer from fermentor to filter
  • diatomaceous earth dosing tank make-up water
  • bright beer exiting the filter at the start of the filter run
  • beer just entering the bright beer tank
  • bright beer entering the filler bowl.

It is important to analyze samples in situ at least every couple of minutes to see the rise or fall of dissolved oxygen levels. Samples left standing, such as beer in bright beer tanks, will show a decrease in the total dissolved oxygen levels over time as a result of reduction of the oxygen compounds in the wort or beer. Beer going to packaging should have dissolved oxygen levels of less than 50–70 ppb (5).

table i

Optimum pH Ranges During Brewing Steps


Optimum pH Range




5.0–5.7 (should not go below 4.8)





Rinse water

same as source water

By tracking the dissolved oxygen content of several brews from start to finish, the source of oxygen pickup — such as pump seal leaks — can be pinpointed and corrected. With a quality assurance/quality control (QA/QC) program involving dissolved oxygen testing, the stability of your beer can be increased significantly (by a matter of weeks). Most large laboratory supply companies carry several models of dissolved oxygen meters, from bench models with computer interfaces to lightweight portable models.

Spectrophotometers: Many of the standard methods of analysis of the American Society of Brewing Chemists (ASBC) call for the use of a spectrophotometer to determine physical properties of wort and beer and concentrations of compounds present in them. A spectrophotometer is simply a device that measures the amount of light absorbed or refracted by a sample solution relative to a reference solution. Physical characteristics — color, permanent and temporary (chill) haze, anthocyanogens (precursors of colloidal haze–causing polyphenols), total polyphenols, total sulfur dioxide, total carbohydrates, bittering units, and diacetyl — play an important part in the flavor profile of a beer. By carefully preparing the sample in such a way that a known amount of reagent is used and then measuring the absorbance of the prepared sample, a brewer can determine the concentration of a variety of organic and inorganic compounds including iron and copper.

Even more high-tech, and more expensive, are UV/vis spectrophotometers, which can measure electromagnetic radiation in both the ultraviolet and visible regions of the spectrum. This equipment and its associated accessories are necessary for certain brewing analytical methods. For an instrument suitable for routine lab testing, however, be prepared to spend between $ 1000 and $ 2500, with accessories costing an additional $ 300–1000. As with the dissolved oxygen meter, spectrophotometers are available from laboratory supply catalogs. Used instruments are often available from school and hospital surplus auctions. The most common spectrophotometer in use today is the Spectronic 20 (Bausch and Lomb, Rochester, New York), which usually retails for around $ 1100.


It is important to measure pH throughout the brewing process (see Table I for optimum pH ranges). pH is a measurement of how acidic or alkaline a substance is. The scale ranges from 0 to 14; 0 is the most acidic, 7 is neutral (distilled water, for example), and 14 is the most alkaline. pH is a mathematical representation of reality. The pH value is the reciprocal of the logarithm of the hydrogen ion activity. That means that pH 4 is 10 times more acidic than pH 5, and pH 3 is 10 times more acidic than pH 4.

pH meters are much more accurate than pH strips or pH paper, although pH meters do need to be kept properly calibrated (a relatively easy process). They are also much easier to read than pH strips.

pH is especially important in the mash tun, where alpha- and beta-amylase enzymes work under specific pH ranges. If the pH is too high or too low, enzyme activity will be hampered or even stop altogether. Another important area for exact pH readings is during acid-washing of your yeast (see Part I), during which an excessively low pH may kill off all or most of the healthy yeast. By measuring the pH of the rinse water from cleaned kegs and other vessels you can tell when the rinse cycle is complete.

pH can also be an indicator of trouble. Bacteria can lower a beer’s pH below its normal levels and dramatically affect its flavor.

It is also interesting to note that some breweries decide when to chill a tank by closely watching the pH. As fermentation proceeds, the pH drops. At the end of the yeast’s life cycle, it begins to flocculate and drop out. The pH will stop dropping at the end of fermentation, which indicates that all of the yeast’s activity is complete. This is the time to chill the fermentor.


Each brewery’s needs are unique. The tests and practices that will be most useful need to be selected carefully. The appropriate selection for your brewery will depend on the brewery’s size, its budget for lab equipment, the experience of its personnel, and its area of distribution. We hope that everyone, whether a home, micro-, or regional brewer, will see the benefits of establishing a complete quality control program.

Although this series of articles does not represent a comprehensive quality assurance program, we have tried to touch on what we believe are the most important aspects of such a program. We hope we have laid a foundation and understanding of the basic concepts so that brewers may implement a program that suits their brewery’s needs and resources.

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