When it comes to brewing, distilling, and winemaking, blending is crucial in order to achieve the desired flavor in each batch. The manufacturing process of these beverages is essentially done in batches, requiring repeatability.
Mixing involves controlled stirring of the ingredients, ensuring that the desired flavor is released without compromising the product. It is important for maintaining a consistent temperature profile and has a significant impact on process economics and profitability.
This article from ACE provides guidance on selecting the appropriate mixer for brewing, winemaking, and distillation processes. Although primarily aimed at readers in these industries, the guidelines are applicable to anyone who needs to mix ingredients, especially liquids.
The Importance of Choosing the Right Mixer
Mixing serves three main purposes, often combined together. The first purpose is to disperse one ingredient into another. The second is to ensure even distribution of temperature throughout the mixing tank. Third, agitation is sometimes necessary to prevent particles from settling at the bottom of the tank.
In beverage production, as well as other products, the goal is to achieve uniform blending of ingredients. Failing to do so will almost certainly result in variations in taste.
The tank contents should not have clumps or strings of material. When heating the tank contents, gentle agitation ensures even distribution of temperature. The objective is to counteract the natural convection effects within the fluid, where hotter liquid rises to the top.
The mixing blades and rotation speed determine the level of shear during mixing. Shear refers to the aggressiveness of the mixing process. High shear can damage fragile solid ingredients, although it can also be useful for pulverizing them into finer particles.
While most mixers eventually achieve a uniform distribution when left running long enough, excessive mixing can affect taste and reduce productivity. By selecting the right mixer for the tank and ingredients, the time required for complete dispersal can be minimized.
Types of Mixers
Mixers used in brewing, winemaking, and distilling typically utilize axial flow turbine impellers. In simpler terms, these mixers consist of propeller-like blades at the end of a shaft. The turbine, also known as the impeller, is lowered into the tank and positioned near the bottom. The motor and gearbox are located at the top of the turbine shaft.
There are three types of motors: totally enclosed fan cooled (TEFC), explosion-proof fan cooled (XPFC), and pressurized air motors. TEFC and XPFC motors usually operate at a single speed but can be equipped with a variable frequency drive (VFD) for multiple speed operation. Air motors can efficiently operate at a wide range of speeds but have limited torque and produce excessive noise.
Turbines or impellers have blades that either move or pump the fluid radially or axially. In high shear mixers, the blades are flat and tend to merge into a single disc. This type of “radial flow turbine” drags the fluid in the direction of rotation, with centrifugal force pushing it outward. Low shear mixers have a more conventional blade appearance.
Process Requirements for Brewing
Mixers and agitators are used at various stages of the brewing process, starting from cereal cooking and grain steeping in the mash tun, progressing through brewing, fermentation, and filtering. Consistency in taste across batches of beer requires careful attention to ingredient mixing and temperature control.
Cooking involves mixing cereal grains, such as barley, with enzymes and water before heating. The mixture is usually viscous, requiring a high-power motor for the mixer. Typically, 5 to 10 hp/1,000 gallons is suitable.
Simultaneously, grains are steeped to extract flavor. Initially, the mixer operates at a relatively high speed to ensure thorough wetting of the grains. The speed is then reduced for steeping. A power of 1 to 4 hp/1,000 gallons is usually sufficient. Low shear rates are important to avoid breaking the grain husks into smaller fragments, which could cause filtration problems later in the process.
The steeped and cooked grains are then transferred to the mash tun, where uniform temperature throughout the batch is maintained by agitation. The resulting mixture, called the mash, is filtered through a process known as lautering. The liquid, similar to water but containing beer precursor (wort), is obtained.
The wort is then moved to the brew kettle, where hops are added and the liquid is concentrated through heating. Agitation ensures even distribution of temperature.
After the kettle, the wort passes through a strainer before entering the fermentation tank. Traditionally, the wort would sit in this tank for two weeks or longer, depending on the brewing process. Gentle agitation is used in modern times to keep the yeast suspended instead of settling, which increases the fermentation rate and improves cash flow.
After fermentation, the beer typically undergoes filtration. Precise mixing is required to achieve a uniform slurry when using a filter aid.
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Process Requirements for Winemaking
Winemaking involves the use of mixers at two or sometimes three stages of the process.
The first stage is the mixing of the grape must, which consists of grape juice, seeds, and skin resulting from crushing. Axial flow turbine mixers with a power of 3 to 5 hp/1,000 gallons are typically used for this purpose.
The must is then filtered, and the resulting juice is chilled before entering a fermenter makeup tank. In this tank, yeast and sugar are added, and mixing ensures thorough blending with the juice. An axial flow turbine-style mixer with a power of 0.25 to 0.33 hp/1,000 gallons is usually sufficient.
From the makeup tank, the juice moves to the fermentation vessel. While US winemakers typically allow the juice to sit without agitation, gentle agitation is common in Europe. This is typically achieved with a small mixer of 0.125 to 0.25 hp/1,000 gallons.
Mixers may also be used at other points during winemaking for blending syrups, preparing filter aids, and more.
Process Requirements for Distilling
The process of distilling spirits is similar to beer production. Some form of carbohydrate is cooked and mixed with grains and hops, followed by fermentation and aging.
Similar to brewing, controlled mixing and agitation are required during cooking and steeping. Fermenters are often agitated to keep the yeast suspended. The mixers and agitators used in distilling are typically the same as those used in brewing.
