Efficiency is an important number to understand for all grain beer brewing. Your system efficiency determines the original gravity of the beer as well as how much grain is required to develop a given recipe. Understanding the difference between mash and brewhouse efficiency is also important – as it also drives the grains required.
Efficiency in Brewing
Lets start with a discussion of the basic idea of brewing efficiency. When we add grains to our all grain beer, each grain has a potential associated with it. The potential is a measure of how much sugar a given pound of grain can contribute. A pale malt might have a potential of 1.037 for example. Typically to estimate original gravity we take the potential of a grain (1.037 for example) and convert that to points by dropping the 1 and multiplying by 1000. So a pale malt with a 1.037 potential contributes 37 points per pound of grain.
We use these point contributions to directly calculate the potential sugars for the entire recipe. By taking the number of pounds of malt and multiplying by the potential points for each malt we get a contribution for a given malt addition. We then can sum these up for all grains in the recipe to give an overall potential number of points. If we then divide by the volume of the recipe in gallons, we can directly estimate the recipe’s overall potential gravity points for ideal conditions.
For example, if we had 10 lbs of 1.037 malt in a 5 gallon recipe, the overall potential would be (37 * 10 / 5) = 74 points, which would under perfect laboratory conditions give us a beer with an original gravity of 1.074. This is what would be produced if a brewery were 100% efficient.
However, in the real world, no brewing system is 100% efficient. Losses in each step of the brewing process occur, and the difference between the “ideal” gravity and “real” gravity represents the efficiency of the system.
Now that we understand how to calculate the “ideal” potential points for a recipe, we can talk about the difference between mash and brewhouse efficiency. Mash efficiency is simply the percentage of “potential” sugars that are extracted from the grains during the mash. It is typically a percentage in the 80% range. If we take the “potential” points of the grains, and multiply it by this percentage we get the points extracted from the mash.
Using the example above, 74 points * 80% gives us 59.2 points or a gravity of 1.059 going into the boil. However, since the mash efficiency only includes losses occurring during the mash and lauter process, it will give us an estimate of only the boil gravity and not the original gravity of the beer.
A real world brewing system has additional losses after the mash process is complete. These includes boil off, deadspace during the boil and transfer and trub losses (the gunk left after the boil). Each of these will further reduce your original gravity into the fermenter. The number that captures all of these losses plus the mash efficiency is called the brewhouse efficiency. Brewhouse efficiency is typically a number in the range of 72% for most home brewing size systems.
Since brewhouse efficiency includes mash, boil, transfer and trub losses, it can be applied directly to the “ideal” number we discussed earlier. So again using the example from above, our 10 lbs of malt gives us 74 points under “ideal” conditions. Using a system with 72% brewhouse efficiency we come up with a potential of (74* 72%) = 53.2 points which is an original gravity of 1.053.
So brewhouse efficiency is simply a measure of the overall efficiency of the brewing system encompassing both the efficiency of the mash and lauter process as well as losses in the system during boil, transfer and volume lost to trub.
Practical Applications of Brewhouse Efficiency
Brewhouse efficiency generally remains constant from batch to batch when brewing on the same system, so once you dial in your brewhouse efficiency you can use it to build future recipes. To “dial in” your brewhouse efficiency you simply bump it up a bit if your original gravity from a batch comes in high, or lower it a bit if your original gravity comes in lower than expected. Ideally, you should also meausure your volume into the fermenter, as small variations in volume can throw off your estimates.
The one exception is when brewing a “high gravity” beer. Brewhouse efficiency generally goes down when brewing “big” beers, largely because the mash efficiency declines. This is due to the fact that you are brewing with a much higher proportion of grains to total water used. You won’t extract as much sugar as you normally would when brewing a high gravity beer. As a result, you should lower both the brewhouse and mash efficiency when building a high gravity recipe.