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1 November 2005

Watch the water

Successful brewing looks to liquid analysis.

By Dave Anderson

Because so many factors affect the taste, quality, and consistency of beer, it could be presumptuous to try to isolate liquid analysis as a significant governing element in brewing. But as one famous old beer ad used to say, "It's the water."

Beer is a highly corrosive liquid. It is not only acidic but also contains live organisms that can cause bio-fouling and bio-corrosion of the tanks, fluid lines, and other surfaces. Preventing corrosion requires optimal water and liquid chemistry, which is a science in itself. Principal measurements include pH and conductivity.

As in other industries, liquid analysis plays a key role in monitoring the release of wastewater effluent after the final brewing process. You might require chlorine, pH, dissolved oxygen, ORP, and turbidity measurements to assure the effluent meets the requirements of the local water municipalities.

As brewing plants face doing more with fewer people, the efficient use of modern, online, continuous liquid analysis techniques can keep brewers constantly informed of the state of the process without the need for more personnel. As beer production has moved from a subjective art form to a reproducible scientific process, online analytical instrumentation has become more a part of the brewer's arsenal.

Mashing

Even brewers who know little about chemistry understand the significance of mash pH (acidity or alkalinity) to their final product. Of course, the purpose of the mashing process is to extract starch from the malt and convert it into fermentable sugar, which yeast will later convert into alcohol and carbon dioxide. The two enzymes responsible for starch conversion, alpha- and beta-amylase, function optimally at a pH of approximately 5.5 to 5.6. The pH of the mash will determine how much grain starch will turn to maltose and how much will be dextrins. A pH in the lower part of the range, even as low as 5.0, will produce beers of drier taste, less body, and lower malt character. A pH around 5.7 will produce heavier-bodied, sweeter beers. Controlling pH also helps accelerate the process and provides better foam control.

Three factors impacting pH are: the type of malt employed, the alkalinity of the water, and the mashing method. Since water is the number one ingredient in beer, it's critical to understand the pH of the water it uses. Excessively alkaline water will raise the pH of the mash, thus reducing the enzymatic reactions. You can control this, however, with calcium that will react with phosphates in the water and proteins in the malt to lower pH. Carbonate ions will have the opposite effect. Malt selection also impacts pH. Darker malts lower pH when they interact with the alkalinity in water. Consequently, the production of paler beers like pilsners requires adding calcium to alkaline water since the light malt will not lower the pH.

Brewers have traditionally measured mash pH off line, meaning they periodically extract samples of the water and mash and take them to a laboratory for testing. As the industry expects brewers to do more with less, however, adding continuous, online pH measurement can reduce labor requirements. An online measurement requires a pH analyzer and one or more pH sensors. Non-glass pH sensors meeting brewing industry standards are now available. You can also equip these cost-effective instruments with digital communications capability, making it possible to monitor and control them from a remote or central location. This increases efficiency and reduces the need for personnel. You would typically insert the sensors into the mash vessel using a tri-clover fitting.

Lautering

While the impact of hot-side aeration (HSA) may be controversial, general belief is excessive oxygen uptake at the lauter tun might contribute to long-term flavor instability, reduced shelf life, and potential clarity problems. To avoid HSA, try online dissolved oxygen monitoring. Sensor development in the last two years allows accurate monitoring of trace levels of dissolved oxygen in beer. Make sure sensors you place inside the lauter tun have a robust membrane and can withstand 30 to 50 clean-in-place (CIP) cycles before you replace them.

Clarity is an important issue in quality beer production, and while the clarity of the wort at the lauter tun will never resemble finished beer, it should not be excessively cloudy. You can maintain appropriate clarity without excessive man hours by an online turbidimeter to measure turbidity. In some cases, it can also measure suspended solids. In the lauter tun, a turbidimeter can act as a control point to re-circulate the cloudy wort and draw off the first wort when clarity improves. It can also control the knives in the lauter tun during pumping of first wort and during sparging based on the turbidity levels.

Also at issue at this brewing stage is the question of over-sparging, which can impact the taste of the beer. Over-sparging occurs if the sparge water in the lauter tun goes above 7.0 pH. Reducing the pH of the sparge liquor to between 5.2 and 6.0 reduces extraction of undesirable silicates, tannins, and polyphenols from the mash bed that can contribute to harsh flavors, hazes in the finished beer, and decreased stability. Placing a pH sensor in the sparge water will help maintain balance and eliminate this potential problem.

Brew kettle

One of the principal reasons to boil wort in the brew kettle is to coagulate proteins that have bound with tannins forming a substance called hot break or trub. Hot break is responsible for chill haze; you must remove it. The formation of hot break is dependent on, among other things, the pH of the wort. Measure the wort, and adjust it to optimize break formation. Wort pH determines the solubility of hops added to the process at this stage. Controlling the pH positively affects the body, palate, and clarity of the finished product. A pH between 5.2 and 6.0 is desirable. Anything much below 5.2 can result in a poor break. You can generally control wort pH by adding acids, such as phosphoric acid.

As in the mashing phase, manufacturers have traditionally measured wort pH by removing a sample from the brew kettle and taking it to the lab for pH analysis. The move today, however, is to continuous, online pH measurement that allows a tighter control of the wort pH. Since accurate pH readings are dependent on temperature, online, automated pH analysis eliminates inaccuracies that can occur due to temperature changes going to and from the lab with the wort sample. Non-glass pH sensors are usually the instruments of choice for wort pH measurement.

Following the rolling boil (wherein you boil off volatile compounds that can spoil the beer's taste), quickly cool the wort to prepare it for yeast pitching and fermentation. At this point, measure dissolved oxygen in the cooled wort to be certain the environment is appropriate for the yeast. To maximize yeast activity, you may need to monitor sterile air or oxygen. The dissolved oxygen sensors designed for carbonated beverages are appropriate for this task.

Fermenting and aging

Oxygen is essential for yeast health, and yeast produces beer. Oxygen maximizes yeast activity, causing conversion into alcohol, and also prevents unwanted byproducts such as higher alcohols, esters, diacetyl, and sulfur dioxide. Add oxygen to the cooled wort often in the range of 8-12 parts per million. Inadequate oxygenation can result in poor yeast health and performance, along with stuck fermentations and beers that don't properly attenuate or reach their expected terminal gravity. It's customary to scrub out excess oxygen during the subsequent fermentation. But oxygen added after the respiration phase of the fermentation process has begun (during which the yeast consumes the oxygen and lowers the pH of the wort, making it acidic and anaerobic) can result in staling and off-flavors. Your best bet is to measure dissolved oxygen continuously during fermentation using one of the new FDA-compliant dissolved oxygen (DO) sensors sensitive enough to detect oxygen below 10 parts per billion.

It's also important to maintain optimal pH levels during the fermentation pro-cess to promote conversion to alcohol and ensure consistent end-product quality. Vigorous fermentation lowers pH. Desirable levels range from 4.0 to 4.5 for ales and 4.4 to 4.7 for lagers. Among the benefits of the low pH is its ability to prevent microbial growth in the developing beer. In fact, a change of pH after fermentation can signal potential contamination. Non-glass sensors accurately measure real-time pH in the fermenter as opposed to taking samples to a lab. Remove the sensor during CIP operations.

The fermentation process produces large amounts of carbon dioxide. This CO₂ vents from the fermenter; you can collect it for adding later into the process or sell it for other uses. When specific gravity reaches appropriate levels, seal the vent tube to allow the remaining CO₂ to enter the beer. Later, after cooling, you can add additional carbon dioxide to adjust the final product. During both of these stages, monitor CO₂ purity for the vented gas using a non-dispersive infrared analyzer.

Turbidity measurement also plays a critical role in filtering and fermentation. During fermentation, if turbidity is high, you can re-circulate the wort until it meets turbidity specifications. During the filtering stage, turbidity monitors the beer for cloudiness versus clarity, allowing removal of undesirable suspended particles. Install the turbidity sensor directly in the mainline, making the piping arrangement easier, saving costs, and ensuring beer quality.

Conductivity analysis is also significant in fermentation. After fermentation and cooling, the yeast settles to the bottom of the fermentation tank and needs to be separated from what is now beer. As you empty the tank, you can use conductivity sensors to detect the slight change in conductivity occurring between the beer and the yeast, thus allowing automation of the yeast harvest. Using online conductivity here lowers costs because it reduces loss of bright beer and reusable yeast.

Finishing, packaging

Introducing too much oxygen during purification, aging, filtration, and filling will often result in skunk beer or affect the beer's shelf life. Excess oxygen can also cause dimethyl sulfide (DMS) formation. It's essential to use FDA-compliant dissolved oxygen sensors during these last brewing steps. Because you must maintain a minimal oxygen environment, don't let dissolved oxygen measurements be affected by flow rate. The sensor should be designed to experience minimal drift in low-flow environments.

Utilities

Manufacturers will often run raw water through a membrane-based reverse osmosis water purification system before using it in brewing. The success of reverse osmosis (RO) systems depends on the health of the semi-permeable membranes, especially since these membranes represent a considerable capital investment and are time-consuming to replace. If the membrane clogs up with suspended solids or microbial growth, it can significantly reduce the effectiveness of the water purification process. To prevent this, add acids and other chemicals to the water, but these can represent a threat to the membrane and the quality of the water if you don't monitor them correctly.

Measure the efficiency of the RO system by continuous contacting conductivity analysis. Place one conductivity cell at the RO input and a second on the outlet. A conductivity ratio analyzer measures the conductivity of each cell and calculates percent passage or rejection providing alarms when the membranes need attention. Some breweries prefer to minimize the amount of oxygen content in the water used for production, so this water is degassed of oxygen. In these cases, operators can use a dissolved oxygen sensor to monitor and control the oxygen in this degassed water.

Conductivity measurement is important in monitoring CIP processes, assuring wetted parts remain sterile, and eliminating cross-contamination between brew campaigns. Toroidal conductivity sensors monitor the strength of cleaning chemicals and the efficiency of the cleaning phases, including caustic, acid wash, and clean water rinse. Toroidal sensors have a design that can withstand the harsh chemical environment. Use contacting conductivity sensors in the rinse water cycle if you require low conductivity.

Behind the byline

Dave Anderson is Industry Manager, Emerson Process Management, Rosemount Analytical in Irvine, Calif.