The Brewing Process
Milling: Whole malted barley is milled in a specially designed roller mill. Such a mill will keep the husk of the kernel in one piece as much as possible while the inner starchy endosperm is crushed to form grits. The milled malt is called "grist". The milling of malt for one brew will take about one hour and may incorporate a few different types of malt depending on the beer style desired. The grist is recovered into a grist hopper. Consideration is given when milling and transporting grist as to not fragment the husks which causes astringent flavors and stability problems.
Mashing: The grist is evenly mixed with brewing water and led to the mash tun. The mashing process involves the chemical degradation of malt components by enzymes. The extent of this process is controlled by the mash program which is a timed schedule of temperature changes and rests. This process can take 1 to 3 hours depending on the type of beer desired and the malts used. Design parameters for mashing equipment include accurate and complete control of the mash program, minimize oxygen pick up, reduce shear stress from mash mixer and/or pump.
Lautering: This is traditionally how the sweet malt extract (wort) is separated from the grain. The mash is allowed to settle which creates a grain filter bed (~10 min.). The wort is recovered from below and recirculated to the top of the lauter tun until it runs clear (~10 min.). Once clear, the wort is led to the brew kettle. Hot water (sparge) is sprayed on top of the mash to leach out the sweet wort from within the grain. Separation of wort from grain can take 2 hours or more. At the end of this process the spent grains can be discharged from the lauter tun. Proper lauter tun design and operation will efficiently yield the best sweet extract and less of the unwanted malt constituents.
Boiling: The wort is boiled during which time hops are added. Boiling the wort isomerize the hop oils, drives off unwanted volatile substances, coagulates and precipitates other unwanted substances and sterilizes the wort among other things. Many complex chemical changes take place during the boil. An evaporation of 7 to 10% of the total volume is desirable. 90 to 120 minutes boiling is normal to achieve this. Kettle design considerations have these goals and energy efficiency in mind. Evaporation rate, convectional movement and hot break formation among other things are important kettle attributes.
Whirl pooling: After the boil, the wort is pumped through a tangential inlet to whirlpool (15 min.). The wort is allowed to settle until it is still and clear (30 min.). This process will leave the substances which were coagulated and precipitated during the boil into a compact mound at the bottom and center of the whirlpool. The clear wort can then be separated from the unwanted "trub or hot break". Design parameters for the whirlpool allow 100% removal of the trub from the wort. Tank design and dimensions, tangential inlet proximity, inlet velocity are among the considerations of a well functioning whirlpool.
Casting out: The clear wort is pumped from the whirlpool through a heat exchanger to quickly chill it to fermentation temperature. Pure yeast and pure oxygen are introduced as the wort is recovered into the fermentation vessel (50 min.). As soon as the wort is chilled, all equipment coming in contact with the product must be aseptically cleanable. Hot water at or above sparge water temperature (180°F) at a 1 : 1.11 wort to water ratio should be recovered from the chilling of wort.
Fermentation: Cooling the wort causes another, different fraction of the wort to precipitate. This is separated from the wort either before fermentation or before conditioning the beer. During this time the yeast uses up the available oxygen and increases in numbers by cell division. The yeast then begins fermentation where it metabolizes the available nutrient and chemically changes the wort into beer. Fermentation can take up to several weeks depending on the style of beer to be produced.
Conditioning/Maturation: After fermentation the yeast will further metabolize some of the by-products which it produced earlier. The beer is chilled to near freezing and held there for several days to several weeks depending on the desired beer. Many chemical processes take place during this time which make a clean, good tasting, homogeneous beer. Extended conditioning time naturally clarifies the beer.
Clarification: The beer is clarified by means of a centrifuge and/or filter. The clarified beer is recovered into the brite beer tank from where it is pumped to a packaging line. Beer is filtered to various extents to give shelf stability and/or to give a brilliant color. Sterile filtration is one way to ensure microbiological stability. This process strips the beer to remove bacteria which may have inadvertently been introduced during the process. Filtration to below one micron also strips some flavor and mouth feel components of the beer.
Pasteurization: Pasteurization is another way of making the product microbiological stable and thus can increase shelf life. It is the heating of the product to kill any bacteria which it may contain. A flash pasteurizer (heat exchanger) is employed between a filter or centrifuge and the brite beer tank. A tunnel pasteurizer is employed after the product has been filled into containers.
Potential pitfalls in the brewing process:
There are many ways to introduce off flavors in the process of brewing. Everything from the choice of the raw ingredients to how the beer is served will affect the product quality. The following are some considerations when trying to make good beer.
The brewer should choose barley and wheat malt by the malt analysis provided by the supplier and whenever possible double check these values in house. If the malt consistency is changing, then the brewer needs to know this and how to deal with it in the brew house. Likewise for hops, changing alpha acid content and kettle cast out volumes will necessitate the brewer to vary the amount of hops added per brew to give the same bitterness quality. Malt and hops can also deteriorate in storage.
The water chemistry in most areas is changing throughout the seasons. A brewer needs to understand the chemistry of water, brewing and fermentation in order to have some control over these processes. Detailed record keeping will make for better quality control, comparisons and trouble shooting before a problem arises.
The management of yeast and fermentation is critical to consistent beer quality. Yeast should not be re-pitched to many times. The number of generations is related to the yeast, the process and the equipment employed. Fermentation temperature control and yeast viability is important to keep the amounts of fermentative byproducts at consistent levels.
Regimented cleaning programs will keep the beer spoiling micro organisms in check. Proper equipment design will allow cleaning in place (CIP) systems to be effective in combating infections.
Oxidation chemically ruins the flavor of beer over time, therefore oxygen
pick up must be avoided throughout the process and packaging. Oxygen levels
below 0.2ml per 12 ounce bottle should be achieved for a shelf life of
several months, providing the product is microbiological stable. Oxidation
is slowed down with lower temperatures, so cold storage from brewery to
customer is preferred.
4018 US Hwy 93 N., Stevensville, MT 59870 U.S.A.