Over the centuries, brewing has been considered an art form, but today's brewers are also concerned about consistent quality and maximizing shelf life. Modern brewers use a scientific approach to brewing through on-line liquid analytical and measurement devices resulting in better process control. Here are the key steps in creating a consistent beer.
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 largely determine how much grain starch will turn to maltose, or malt sugar, and how much will be dextrin, a carbohydrate. 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. Control of pH also helps accelerate the process and provides better control of foaming.
Excessively alkaline water will raise the pH of the mash, reducing the enzymatic reactions. This can be controlled, however. Calcium 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 the addition of calcium to alkaline water since the light malt will not lower the pH.
The pH sensors designed for use in food and beverage applications measure pH during mashing. Generally, they measure the pH of water additives and are connected to analytical instruments with digital communications capabilities. This makes it possible to monitor and control them from remote locations, increasing efficiency and reducing personnel time.
After mashing is complete, the mash is delivered to the lauter tun.
It’s usually accepted that excessive oxygen uptake at the lauter tun may contribute to long-term flavor instability, reduced shelf life, and potential problems with clarity. To avoid excessive oxygenation, on-line dissolved oxygen monitoring is performed using sensors designed specifically to accurately monitor trace levels of dissolved oxygen in beer.
Clarity is an important issue in the production of quality beer. In the lauter tun, a turbidimeter can act as a control point to recirculate the cloudy wort and draw off the first wort when clarity improves. It can also be used to control the knives in the lauter tun during pumping of the first wort and during sparging based on the turbidity levels.
Also at issue during this brewing stage is the question of “oversparging” which can impact the taste of the beer. Oversparging 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. A pH sensor placed in the sparge water will help maintain balance and eliminate this potential problem.
One of the principal reasons wort is boiled 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 and must be removed. Chill haze means the beer will appear clear at room temperature, but appear turbid when refrigerated. The formation of hot break is dependent on, among other things, the pH of the wort. The wort must be measured and adjusted to optimize break formation. In addition, 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. Much below 5.2 can result in a poor break. Wort pH is generally controlled with the addition of acids such as phosphoric acid.
Following the rolling boil wherein volatile compounds that can spoil the taste of beer are boiled off, the wort is quickly cooled in preparation for yeast pitching and fermentation. At this point, dissolved oxygen should be measured in the cooled wort to be certain the environment is appropriate for the yeast. To maximize yeast activity, sterile air or oxygen may need to be monitored.
Fermenting and Aging
Oxygen maximizes yeast activity causing conversion into alcohol, and also prevents unwanted byproducts such as higher alcohols, esters, diacetyl and sulfur dioxide. Oxygen is added 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. Excess oxygen is usually scrubbed out 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. Dissolved oxygen is best measured continuously during fermentation using FDA-compliant DO sensors sensitive enough to detect oxygen below 10 parts per billion.
Optimal pH levels must also be maintained during the fermentation process 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.
Turbidity measurement also plays a critical role in filtering and fermentation. During fermentation, if turbidity is high, the wort can be recirculated until it meets turbidity specifications. The turbidity sensor is installed directly in the mainline, making the piping arrangement easier, saving costs and assuring the quality of the beer.
After fermentation and cooling, the yeast settles either to the bottom of the fermentation tank or rises to the top and needs to be separated from what is now beer. As the tank is emptied, conductivity sensors can be used to detect the very slight change in conductivity that occurs between the beer and the yeast, allowing automation of the yeast harvest. Using on-line conductivity at this point lowers costs in that it reduces loss of both bright beer and reusable yeast.
Monitoring pH, dissolved oxygen, turbidity and conductivity — clearly, the informed use of liquid analysis helps produce optimal beer quality at the highest efficiency and lowest production cost. A scientific answer to an age old art.
About the Author
Dave Anderson is the industry marketing director at Emerson Process Management, Rosemount Analytical. He has more than 20 years experience in various process industries. For more information, please visit www.RosemountAnalytical.com.