It is brew day again, and you have decided to make an old favorite, your Old Growth Lager. When you made this brew last summer, it was a real hit, so you figured a repeat performance was in order. Unfortunately, the hop supplier has run out of the German Hallertauer you used last year, and several of the malts are not available either. So you substitute some different malts and hops, but you are not quite clear on the proper proportions you should use for these different ingredients.
There is a solution, of course, and that is to use standard brewhouse calculations to create a beer as close as possible to the original using these different ingredients. Brewhouse calculations should be used every time that you brew a new recipe or change the formulation of an old one. They can help you determine the grist bill and hop bill, along with the strike water volume and temperature.
Brewing calculations are also essential when brewing for competition. One fundamental aspect of brewing for style is keeping your beer within guidelines for color, bitterness, and alcohol content. Predicting these aspects and controlling them when creating or experimenting with recipes is simply a factor of knowing the (simple) math.
Many of these brewing calculations are approximations, and there are more accurate ways to calculate your brew, but these calculations will do for most homebrewing applications.
All you need to get through these calculations is a basic understanding of algebra. Calculating your brew may seem dry and tedious, but it does give purpose to those years of mathematics you took way back when. Of course if you are an engineer, you actually like algebra, so grab your calculator and get your best pocket protector ready!
To effectively use these calculations you must have already determined several parameters of your formulation, which include:
Total bitterness (IBUs)
Hop alpha acid
Original gravity (°Plato and SG)
Brew volume (gallons)
Mash temperature (°F or °C)
Wort color (°Lovibond or SRM)
There are several other parameters that will be determined during the calculations. First convert your starting gravity (SG) to degrees Plato (you will need to use both of these measures to determine the grist bill). What is Plato? It is roughly the percentage of total solids (which are mainly sugars) in solution. Why do you need to know Plato? Because he was one of the most profound philosophers of all time.
°P = (SG-1) x 250
Now enter your numbers into the following formula:
lb. malt = (8.34)(gallons of wort)(SG)(°P) BE
The BE is the Brewery Efficiency, and it is a term for how much extract you get out of your malt in your brewery. (A BE of 69 means that you are extracting 69 percent of the available extract from the malt.) Typical numbers are:
Pale Malt 69
You may choose to use the same BE for specialty and pale malt if you wish (generally speaking, the extract you can get from specialty malt is less than from pale malt). Once you know the total malt weight, you can determine the percentage of each malt type that you wish to add.
With the total grist bill determined, you can calculate the color of the beer, which is relatively simple. You need to know the color specification for each malt (in degrees Lovibond) that you are using, and calculate the percentage of the total grist for each malt as well. Multiply the percent of the malt by the color of the malt, and add all the values to give an approximation of the beer color.
A result in the 2 to 4 range is a pale yellow beer (think Budweiser), 8 to 17 is amber (Anchor Liberty is 8° Lovibond, Michelob Classic Dark is 17°), 21 to 23 is brown (Henry Weinhard’s Dark), and much higher is black (Anchor porter is 58).
Wort Color = (% malt)(malt color)
You should keep in mind that the color of the beer is simply an estimate of the beer color and will vary from formulation to formulation. You can’t always achieve the same color by using a darker malt in smaller proportions because the shade of the color
may change even though the value does not. But this calculated value is a good way to estimate your overall beer color.
Strike Water Calculations
Now it’s time to examine the strike water, both for volume and temperature. We will use the standard measure found in most homebrewing texts to express the liquor-to-grist ratio, which is:
qt. of water : lb. of grist
Often the ratio is somewhere between 1:1 and 1.5:1, and the greater the ratio, the thinner your mash (which will affect enzymes in the mash). Once you decide on a liquor-to-grist ratio and a mash temperature, you measure the malt temperature with a thermometer and can calculate the strike water temperature with the following
Strike temperature = (0.19)(mash temp.-malt temp.) +mash temp.(liquor:grist)
The final part of your calculations will be hop bitterness. If you are like most homebrewers, you probably figure the more hops the better. But to really impress your drinking buddies with that 100 IBU (International Bittering Units) beer, you need to do the bitterness calculations.
You have to decide on the amount of IBU that you want in your style of beer and have to know the alpha-acid content of each of the hops you will be using. Normally this alpha-acid content
is listed on the hop package that you purchase.
You also need to determine the utilization rate of the hops you are adding, which depends on many
factors, including the form of hops you are using (such as whole hops, pellets, extract) and the length of time the hops are in the boil. In reality the hop utilization rate is actually a fudge factor that you determine with experience. For now you can use the following numbers for whole hops or pellets:
Once you have determined the utilization for each hop addition, you can find out how much of each hop you need to add to achieve the required bitterness.
You need to decide how much bitterness you want from each hop that you are adding, and you need to use this amount in the following calculation (don’t just use the total bitterness in this calculation). An important note: You should express the percentages in these calculations as a decimal (for example 5 percent = 0.05).
Ounces of hops =(gal. of wort)(IBU)(% alpha)(% utilization)(7,500)
You can calculate the bitterness contributed by the aroma hops by first deciding the number of ounces you want to add, and then calculating the bitterness they contribute:
IBU = (oz. hops)(% alpha)(% utilization)(7,500)(gal. of wort)
By adding the IBUs from each of the previous calculations you can find the total IBUs for your beer. How do you decide which calculation to use? It all depends on whether you want to add the hops by weight (for aroma) or by bitterness (for bittering). On the other hand if you’re like a lot of homebrewers, you just throw in a few pounds extra anyway.
By using these calculations consistently you can help in consistent brewing that allows you to deal with changes in your raw materials or brewing process. But keep in mind that just because two brews have the same specifications, they won’t be identical. Many of the differences in the qualities of raw materials are not expressed in the values you can calculate. And if you get bored or tired doing these calculations, you can always program them into a computer spreadsheet. Or just sit back and have a few more brews.
David Sohigian is lead instructor at the American Brewers Guild, Davis, Calif.