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All Grain Boil

There are several very important things which take place in the boiling kettle of an all-grain beer. The most obvious is perhaps simply that the wort gets sterilized with the high temperature. Along with this, however, are factors which directly and in some cases dramatically affect the final product : your beer.

Most home brewers have read that a vigorous rolling boil is paramount in the making of a good brew. The physical motion of a good rolling boil plays two key roll. First of all, it helps coagulate proteins, giving a good hot-break which will sediment out either in the kettle itself, or later in the fermenter (depending upon the chilling method employed), thus providing for a much clearer beer. This physical action is also required for the isomerisation of hop oils, so without it hop extraction efficiency would be greatly reduced.

Another thing most home brewers know is that the lid must be kept off the kettle during the boil. Well, this isn't entirely true, actually. It should be more properly stated that the lid should not be kept completely on during the boil. One reason for this is simply to allow for evaporation. In most cases you collect up to 50% more wort during the sparge than we actually want to go into the fermenter. Our volume is reduced to the desired level by evaporation during the boil. Another key reason for not having the lid on completely is to allow the evaporation of certain unwanted compounds, such as DMS (dimethyl sulfide), which can cause cooked-corn like flavors in high enough concentrations.

It may seem obvious at this point that keeping a good rolling boil is not always possible when the lid is off the pot. This is especially true if you use a lower-output heating element With our 85K BTU propane burner, with 5 gallon batches we can keep a good rolling boil with no trouble at all even when the lid is completely off the kettle. But when we do 10 gallon batches (which is most of the time), we have to leave the lid on 75% in order to maintain the same level of boil. This is perfectly fine, and will still allow DMS to evaporate. Just keep in mind that evaporation levels will vary dramatically from having the lid off completely, so your final volume will be a fair bit greater than it would if the lid were off. There's no real formula which can tell you how much liquid will evaporate during the boil, as it depends entirely on the equipment you use, the length of the boil, as well as the position of the lid, and even on the ambient temperature of the brew area (lower temperature gives higher evaporation). Over a standard 60 to 75 minute boil, you can expect a 20% to 50% reduction in volume. It should only take a couple of batches to figure out exactly what the rate will be for your individual system, and you'll be able to use this value for planning future batches.

During the first 10 to 15 minutes of the boil, a brown scummy skin may form over the surface of the boiling wort. This is the coagulated proteins of the hot-break, which we recommend you skim with a sieve or spoon, and discard. Many knowledgeable brewers actually recommend waiting until this is skimmed before making the first hop addition to the kettle. Firstly, it is easier to skim without the interference of hops. But more importantly, some theorize that waiting this amount of time can actually help you get a better extraction from your hops. Al Korzonas (Home brewing : Volume I, p76) believes that "since the hops help form the hot break, some of the hot break will coat the hops interfering with the extraction of their bitterness".

There are many different theories on exactly how long your boil should be, and we certainly aren't the ones to give you a definitive answer to that question. All of these theories agree, however, that once hops are added to the boil, you need to boil for at least 45 to 60 minutes in order to get a decent hop utilization ("decent" being in the neighborhood of 25% to 35%, depending upon your system, meaning that even in the best case, as much as 3/4 of your hops is going to waste. Sorry, but that can't be avoided). If you boil less than 45 minutes, hop utilization will decrease quite dramatically. Ourselves, we usually boil for 15 minutes before our first hop addition, then we skim the break, make our first hop addition, and boil for 60 minutes after that (possibly making further additions according to the recipe being used). The best advice here is to find a boiling schedule that you like, and then use it, and learn how it performs with your system. As with most aspects of brewing, we recommend sticking with a method at least long enough to come to understand how it works for you with your system. Flailing about with your techniques from one batch to the next may be fun, but it won't lead to as great an understanding of those techniques as could otherwise be the case.