The first job of the wort kettle is to prevent the sweet nectar that was the result of mashing from spilling all over the brewhouse floor. After all, we need somewhere to put the run- off and a proper wort kettle is excellent at preventing this. Wort kettles are equipped with some kind of heat source. They vary in design from direct fired to steam jacketed as a means of applying heat energy to the wort. In some brewhouses a device known as an external calandria is utilized. In this situation a pump moves the wort through an external tube equipped with heating coils and the wort is boiled in this manner. More modern brewhouses use an internal calandria. The heating column is located inside the kettle and convection rather than a pump is used to continually supply wort to the heating tube.
One of the main reasons for wort boiling is the sterilization of the wort. This conveniently establishes a point in the process when the wort is devoid of unwanted wild yeast, fungi and bacteria. Brewer’s refer to all steps before post boil cooling as “hot side”. After this we must take great care to ensure sanitary conditions are maintained through a series of cleaning and chemical sanitizing procedures. As you recall from the mashing discussion enzymes are optimally activated by temperature to maximize starch and protein degradation. The boiling wort assures that all enzymes are denatured and the scarification process stops.
Hops are added into the wort kettle at various stages depending upon what their purpose is in the beer. Alpha acid is the bittering agent in hops. The alpha acid must be extracted and dissolved into the wort. One hour of boiling is long enough to isomerize the alpha acid and render it soluble. Boiling also extracts the essential oils from the hops. These are responsible for hop flavor and aroma. These are added later in the boil because extended boiling will send these volatile compounds out the kettle stack and therefore not impart there aroma and flavors to the beer. In addition to this undesirable hop oils, ketones, sulfur compounds and esters are evaporated.
The formation of what is referred to as hot break is another major benefit of the wort boil. During the boiling process, albumin and polyphenols collide in the convective boiling movement. When the boil is done, these precipitate from the mixture and the wort is subsequently removed leaving behind harsh tasting tannins and undesirable proteins that result in haze formation in the finished beer. They are removed by pumping the boiled wort to a whirlpool vessel. The wort is pumped into the tank at a tangent and this results in a spinning mass of liquid in the whirlpool. Particulates including the precipitated proteins and tannins are collected at the bottom center of the whirlpool along with hop material and other solids. This is called the trub (pronounced troob). From here the wort can be rapidly cooled through a heat exchanger and sent on to the unitank for fermentation.
So there you have it, another essential part of beer making. Boiling the wort is responsible for many things from hop oil extraction, sanitization to clarification through protein coagulation. Now my stolen catch phrase from that all too famous credit card company, “The wort boil…drink no beer without it.” Unless of course it’s a Berliner Weiss!
- Joe Schiraldi (VP Brewing Operations)
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