Brewhouse operations consist of three main processes; mashing, lautering and boiling. Inefficiencies in these operations cannot be rectified later on in the brewing process, so it’s vital that equipment is designed and operated correctly to ensure optimum performance.
The brewing process forms the foundation for a quality beer and gives each product its particular characteristics. Brewhouse operations produce wort, a sweet liquid consisting of fermentable sugars and dextrins. The quality of the wort depends to a large extent on the efficiency of the mash mixing process.
The Biochemistry of Mashing
The primary aim of the mashing process is to convert carbohydrates in the grain into a mixture of fermentable and non-fermentable sugars. This is a biochemical process which is driven by the action of two main enzymes, alpha and beta amylase. These enzymes break down the carbohydrate chains into shorter saccharide chains, producing a mixture of simple and complex sugars.
Each enzyme has a temperature at which its activity is optimum. In order to maximize the efficiency of the mashing process, the mash must be heated in stages to correspond to the temperatures for optimal enzyme activity. The mash is held at each prescribed temperature for a length of time to allow the specific enzyme to do its work. At temperatures on either side of the optimal level, enzyme activity is greatly reduced. It is therefore essential that brewhouse operators achieve these temperatures to ensure mashing efficiency.
At the end of the mashing process, the temperature of the mash is raised to a level where the activity of both alpha and beta amylase is terminated. This sets a limit to the amount of fermentable sugars in the wort, and determines the amount of alcohol produced in the beer through the fermentation process.
The efficiency of mashing depends on the design and operation of the mash mixer. Two aspects play an important part:
- The design of the heating jacket
- The design of the agitator
Heating Jacket Design for Mash Mixers
In most commercial breweries, steam jackets are used for heating. Home brewers very rarely use steam as a heating medium and rely on electricity or gas to heat their mash.
Whatever heating medium is used, an important aspect to consider in process operation is the effect of thermal lag. When heat to the jacket is turned off, heating does not stop immediately and some residual heating will take place. Operators need training to turn off the heating to the vessel at the right time to ensure they don’t overshoot the desired temperature.
Steam jackets are located at the bottom of the mashing vessel. In many vessel designs, the side walls are also steam heated. Although this arrangement facilitates a natural convection flow of the mash, it is greatly improved by the use of an agitator or mixer.
The Importance of Agitator Design
Mash has a fairly thick consistency and natural convection cannot be relied on to conduct heat transfer effectively throughout the vessel. Without agitation, there is a very real risk of the mash being scorched when coming into contact with the heating surfaces.
The critical function of an agitator is to ensure uniform mixing and heating throughout the volume of the mash. This not only improves mixing efficiency, but also increases the conversion of carbohydrates and the yield of fermentable and non-fermentable sugars.
The agitator is designed to force the mash downward to move across the heating surface at the bottom, and then up the sides of the vessels. Of major concern for brewers is the amount of shear damage to the mash during this process. Today, most mixers use low shear impellers that run at relatively low speeds to limit the damage to the grain husks during mashing.
Mash agitators and mixers play a critical role in the mashing process. All large breweries use them, and many micro-breweries install them for the production of their craft beers.
Of the three main brewhouse operations, mash mixing plays the central role. A critical element of this process is efficient agitation of the mash. Brewers should not neglect the importance of agitators in mash mixing, and should engage a global supplier of agitators and blending systems to design and engineer this equipment for their brewing operation.