Worts of Wisdom meeting, February 29, 1996 Hopping This is a brief overview of hopping, concentrating on knowing how much to add when to get the bitterness you desire. As we all know hops provide a number of important characteristics to beer. The short list of these is bitterness, hop flavor and aroma, and anti-microbial action. Hop flavor and aroma are classically considered by homebrewers to be contributed by hops added late in the boil, with the idea that the compounds responsible are driven off by boiling. This idea, while largely correct, is given the lie by a number of findings. One, mentioned last month by me in the alt style talk was that very large amounts of early hops (i.e. boiled 60') contribute to a significant hop flavor and even some aroma. This idea is echoed by those who are repulsed by beers that use bittering hops that they don't favor, e.g. Chinook. Another line of evidence is emerging in the homebrewers' arena courtesy, once again, of George Fix. He has written of an old German practice called first wort hopping. Here hoppy styles are made in an unusual way. One third or a similar proportion of the hops are added to the sweet wort as it comes out of the lauter tun. The wort is warm but this is before the boil. No hops are added late. The hop flavor for Pilsners is preferred over all other methods (dry hopping was not tested). This is an area ripe for experiment and I'm sure we'll see more in his new book if it ever comes out. I think what most wanted out of this talk was a discussion of hop bittering. Here the issue is easier to understand than above, but the details are still hotly contested. Bitterness in beer is the result mainly of isoalpha acids derived by boiling hop resins which contain alpha acids. The latter are converted (isomerized) to the former by the heat and agitation of the boil. Beta acids are also a factor, especially in aged hops, but are usually ignored for various reasons. Beer bitterness is measured in the lab by a method that gives a rough measure of the concentration of isoalpha acids. The International Bitterness Unit, or IBU, is, again roughly, this measured in units of mg/L. Homebrewers talk about putting in a certain number of IBU's into their beers. This is a misuse of the concept, if a useful one, as IBU's are measured quantity and don't always reflect bitterness anyway. The way we misuse it is to assume that we know how many IBU's we want a beer to have and how to get that many in there. How many IBU's do I want? Well, that depends of course on the style you are brewing and your own preferences. The taste threshold is about 12-15 IBU's. This is also the level in cheaper megabrews. Most lager styles are in the low to mid 20's, Sierra Nevada Pale ale has about 30-32, an IPA can be twice this, and some barley wines have >100. Many factors, mainly the maltiness and sweetness of the beer, affect the perception of bitterness and go partway to explaining the size of these differences. Check out the AHA style guidelines for an idea of how much you might want for a given style. Ultimately it comes down to your own experience so keep good notes (see below). Now I know how many I want, how do I get them? It is easy to figure out how much alpha acid you have added to the boil, the difficulty comes in figuring the isoalpha acid level. The isomerization takes time so the longer you boil, the more you get. The most isoalpha acids you will ever get is about a third of the alpha acids that you put in. This relationship of time of boil to amount isomerized is called the utilization. Here is the source of argument. Everybody has a different curve that they like showing this relationship. One reason for this is probably that it is different for different people with different equipment. I will not argue this here, only show what I think is a good set of numbers derived through experiment (!) with homebrewing setups. Russ also has some experimentally derived numbers. I have converted the utilization numbers to what I call a time factor. I will explain below how this works, but it simplifies your calculations. For those keeping track, the time factor is 74.9 times the utilization. For a given addition of hops you read the time factor from the graph, based on the wort gravity (in the boil, not the desired final gravity-- those doing partial volume boils will be using higher gravities) and time the hops are boiled. The total "amount" of bitterness added from one addition is the product of the ounces of hops, their % alpha acid (not expressed as a decimal, i.e. 5% is 5, not 0.05), and the time factor. All these "amounts" when summed and divided by the final boil volume, in gallons, give the estimated number of IBU's. To formulate a recipe, decide on the IBU level you want and multiply by the number of gallons you expect to have at the end of the boil for the total bitterness. Set your late additions based on flavor considerations and calculate the bitterness they offer as discussed above. Subtract this from the total to get the bitterness that must be offered by the early addition. Divide this amount by the appropriate time factor and alpha acid percentage to get the ounces of hops. Total hop bitterness [IBU Gallons]=(ounces of hops) x (% a acid) x (Time factor) Oz of bittering hops = (IBU Gallons needed after early hops considered) (Time factor) x (% a acid) Time factor [(IBU gallons)/(oz % a acid)] = 74.9 x utilization Utilization = .397 x 0.000125^(SG - 1.000) x (1-e^(-0.04 x time [min])) Thanks to Glenn Tinseth (gtinseth@teleport.com) for this utilization function. See his hop page: http://www.teleport.com/~gtinseth/