Pressurizable 50 hl Kettle		 There are many “opportunities” throughout the brewing process to make mistakes, some may be realized while proceeding with the process, some are recognized simply when the beer does not taste good. Mistakes can and do happen. They can be corrected either immediately during the same batch or in the next batch.
Boiling, as part of the brewing process, however, is different: it is more important than anything else. It isn’t only turning on the heat on the Kettle and running it for ninety minutes. It requires skills. It requires a properly designed equipment.  It is a process that has to be carried out properly in every single batch, to achieve the desired product: a stable, clear, great tasting beer of balanced character.
So what is really the significance of boiling? Recognizing that this space is hardly enough to even summarize the importance of the boiling, we will try to make a point to get you interested in studying the brewing process in greater depth.
Well, boiling stabilizes the composition of the wort, which is necessary to achieve “a stable, clear, great tasting beer of balanced character”.
This “stabilization” of  the wort happens by the following:
1. Boiling lowers the pH level in the wort, by which a proper environment will be created fot hops utilization.
2. Simple boiling sterilizes by the temperature, by the slightly acidic pH and by the extraction of antiseptic hop resins.
3. Boiling temperature destroys enzymes: if they would not be destroyed, they would continue to work during fermentation.
4. Boiling is the processing environment of the hops.
5. Vigorous and violent (rolling) boiling helps coagulate unstable proteins. This process is assisted by the tannins extracted from husks and hops.
All these (i.e. proper boiling), in turn, create a stable medium for fermentation.

So then, when should it start? What is really a proper boiling? Why is “rolling boil” important? How long should it go? What happens in different stages of boiling? How should hops be added and processed? 
The answers to these questions will be given below from the practical experience of  the co-workers at Bavarian Brewery Technologies, from our customers’ skilled brewmasters and from theoretical works of brewing literature.

STARTING THE BOIL

An old rule suggests not to start boiling before sparging is completed: instead, keep the wort just around or under 160 degrees (F) so any unconverted starch could still be saccharified. Our recommendation, in the light of today’s better quality malts, is to look at the efficiency of your mashing and lautering process (which is partly dependent on your methods, and partly on the quality of the malt), make a statistical observation by comparing final gravities of ten batches both ways, assuming the same malt schedule. Calculate the average gravity at both methods, and, if there is no difference in the results, then you may start heating the wort in the Kettle as soon as wort covers the bottom. Otherwise, wait about 15 minutes after sparging is finished, to complete the saccharification process.


Multi-chamber 10 bbl Kettle		 THE PROPER BOILING

Hopefully, it will not come as a surprise to any practicing brewer that there are different qualities in boiling: simmering, strong boiling, violent boiling, etc. The “violent boiling is also called vigorous or rolling boil. This is the kind of boiling, when the wort is quickly turning around in the Kettle, large by number and huge by size bubbles are created in the bottom of the vessel. The boil will get rolling, if the heated surface in the Kettle is uneven. It is also required that boiling should be strong enough to evaporate at least 5% of the wort in one hour. (Needless to say, Bavarian’s kettle design completely conforms to these requirements and rules.) Discussing proper boil, may we eliminate a Myth: direct fired kettles give more stable beer; the Fact: is that the more stable beer is not the result of the higher temperature, but the result of the violent, turbulent rolling boiling of the wort.

WHY ROLLING BOIL?

Rapid boiling drives out oxygen, which can become very harmful in the process: it can change the color to darker than desired, and it can help serious infections to develop in the beer. Even more important, however, is the break down of proteins. This can be achieved only if boiling is vigorous: it helps create surface tension of the so called “albumin fraction” of the protein. These particles then will concentrate on the wort-air-steam bubbles and because of the high concentration, they will aggregate into larger and larger masses. More scientifically, the micellae, denatured in the boiling process, are held in suspension only by their electric charges. When in turn, the force of affinity between the micellae exceeds the force of  electrostatic repulsion, as a result of  high concentration on the surface of the bubbles, the albumin will aggregate and precipitate. This process cannot be achieved without a rolling boil.

STAGES AND LENGTH OF BOILING

From practical point of view, boiling should not take less than 90 minutes. The specific length depends on the hop schedule. The minimum time is explained by the following. Sterilization requires about 5 minutes. An additional 10 minutes (total of 15 minutes) will kill the enzymes. Another 15 minutes are needed to eliminate tannin originating from malt husks. This first half hour, in case of infusion mash, is to decompose and precipitate some of the proteins. This should be accomplished before hops are added, because otherwise the sticky hop resins will combine with the coarse protein flocks and precipitate out of solution. When decoction mashing is used, excessive complex proteins are usually not a problem. After that, calculate the total time needed to evaporate the desired amount of wort. Subtract the above 30 minutes. The remaining time should include the hops schedule so that the hops should not be boiled longer than one hour. Except for high gravity beers, the total boiling time should not last longer than 2 hours. Boiling the hops longer than one hour will start generating sharp, undesirable and unpleasant flavors. During a long boil a greater percentage of the hops’ bittering and preservative qualities are carried into the finished beer.
Thus, the stages of boiling are characterized by the functions: sterilization, driving out oxygen, killing enzymes, protein break-down, evaporation of water and hops processing.
HOPS PROCESSING

Hops contain two kinds of aromatic material: bitter resins and essential oils. Bitter resins require vigorous boiling and relatively longer time for dissolution. During this, most of the essential oils leave the Kettle with the steam.
Another important requirement for hops processing is the pH level of the wort: it is supposed to be around 5.5 and 5.8 initially. Vigorous boiling will reduce this by 0.2-0.3 to the near minimum level of 5.2 under which no coagulation of proteins takes place. Although hop utilization increases at higher pH, a finer or less harsh bitterness can be achieved at lower pH. According to emp- irical data, the optimum pH level for hop utilization is between 5.2

As we know, tannin combines with proteins in the unoxidized state. These protein-tannin complexes formed with non-coagulable proteins cause chill-haze, because they are soluble in hot wort but precipitate in the cold, and since they are relatively light-weight, they will float and will not totally form sedimentation. Wort should be boiled well before adding hops, so tannins from the husks are eliminated in the hot break, thus reducing the chances of chill-haze development.
The oxidized tannin on the other hand, is called phlobaphene, and it combines with protein. Phlobaphene-protein complexes are insoluble in water, therefore precipitate in the hot break.
Since most of the essential oils of hops are lost in the boiling process, a beer with a good hop aroma requires additional hops after boiling. Finishing hops are usually added within the last minutes of boiling, or as the wort is struck from the Kettle. Often times is done dry hopping, which takes place during fermentation.

Recommended readings
George Fix: Principles of Brewing Science (ISBN 0-937581-17-9)
Lee W. Johnson: Brew Chem 101 (ISBN 0-88266-940-0)
Master Brewers Association of the Americas: The Practical Brewer 
GregoryJ. Noonan: Brewing Lager Beer (ISBN0-937381-01-2)

 
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Bavarian Brewery Technologies - Tel.: (310) 391-1091 - Fax: (310) 391-4530 email:info@bavarianbrewerytech.com