Why is it important? Brew house efficiency will directly affect your recipe formulation and how many pounds of malt will be required to reach a specific OG at a specific volume in the fermenter. Efficiency is determined by calculating the potential amount of sugars in the wort versus the actual amount extract. Calculating number of gravity points: Each grain has a potential gravity – determined by a Congress mash in a laboratory where the grain is milled into a powder and all sugars are extracted. Most pale malts will be around 1.036 to 1.037. The more highly the malt is kilned the lower the potential: Crystal 40 is 1.033 and Roasted Barley being 1.025. 10 lbs of 1.037 malt in a 5 gallon recipe, the overall potential would be (37 * 10 / 5) = 74 points Only applies to All-Grain Brewing! Extracts are always 100%. Mash efficiency: percentage of “potential” sugars that are extracted from the grains during the mash. Should be measured before the boil. Brewhouse efficiency: 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. 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.

Improving your efficiency:

1. Improve the Milling of your Grains The crush of your grains makes a significant difference in the efficiency of your mash and sparge. Grains should be finely crushed, but the milling should leave the hulls largely intact to act as a filter bed. Note that if you crush your grains too finely you will plug up your filter bed resulting in a “stuck mash”. If you get a stuck mash, your filter bed will clog up and the wort will stop flowing. Too fine a crush can also cause tannin extraction. What you want to see is few or no uncrushed kernels, plenty of kernels broken into two to four pieces and a minimal amount of flour. Most mills come pre-set to 37 mil (~0.9mm) – decreasing to 14 mil (0.35mm) can increase yield by ~10%.
2. Mash Out or Sparge with Hot Water Hot water during the mash out and sparge helps the sticky wort flow more freely. Ideally you would like to raise the mash temperature to about 168F and then use 168F water to sparge. A mash out infusion addition can be used to help raise the temperature of your mash as you sparge. Over 170F can cause tannin extraction if the pH starts to increase. Tannin extraction is not an issue during batch sparging or BIAB.
3. Sparge Slowly Most beginners attempt to sparge their mash much too fast. Sparging too quickly leaves insufficient time for the hot water to extract the sugars in the grain bed. Limit the flow out of your mash tun to just above a trickle. It should take 30-50 minutes to fully sparge a 5 gallon all grain batch (about 6 gallons of wort).
4. Minimize Losses in your System Losses anywhere in your brewing system, including deadspace in the mash tun, transfer lines, pumps, and trub at the end of the mash result in lost wort. The lost wort takes sugars with it, reducing your overall brewhouse efficiency. Use a properly sized mash tun, and work to eliminate deadspace in the system.
5. Properly Designed Mash Tun For continuous sparging: The design of your mash tun and false bottom or screen can have a huge effect on the efficiency of the mash process. A round, cylindrical mash tun is generally considered best, as it leaves the depth of the grain bed about equal to its width. This is one reason cylindrical water coolers are popular. The false bottom ideally will cover the entire bottom of the mash tun but have minimal deadspace underneath it. This will provide an even flow across the entire grain bed giving better efficiency. Too fast of a flow can create water channels. Too slow can compact the grain bed and also create water channels to form. The goal is to rinse the grain column evenly. For Batch sparging it really doesn’t matter…as your goal is to drain the entire volume.
6. Mash Thickness The thickness of the mash doesn't seem to effect the fermentability of the wort that is produced but thinner mashes can significantly improve the conversion efficiency. As a result brewers who see low efficiency from their mashing may try to use a thinner mash (1.5 - 2 qt/lb) as they are shown to convert more starches. While thick mashes help to stabilize the enzymes which makes them active for a longer time, they also inhibit their activity (substrate inhibition) and make it more difficult for the starch to gelatenize. As a result in thinner mashes the conversion processes occur faster.
7. Sparge more wort Having a larger preboil volume (which will require a larger boil-off to get to the desired post boil extract/gravity) increases the lauter efficiency by increasing the dividend in aforementioned equation. In simple terms, the more water that is available for rinsing out the extract, the higher the lauter efficiency will be. But the boil-off should only be changed within a limited range. Excessively long boil times or excessively strong boils (hourly boil-off of 15% or more) can be detrimental to the beer quality.

For batch sparging each additional sparge step (run-off) will bring more of the extract from the mash into the boil kettle and thus increase the efficiency, it should be taken into account that, in order to keep the pre boil volume the same, the size of the run-offs has to get smaller as their number is increased. That reduces the efficiency of the sparge steps and as a result a diminishing return is achieved by adding more run-offs. As a result there is a limit to the batch sparging lauter efficiency which is set by the amount of grain and the targeted pre-boil volume. Going from a no-sparge (1 run-off) to a single batch sparge (2 run-offs) gains about 8% lauter efficiency, while going from a single batch sparge to a double batch sparge (3 run-offs) gains only about 2-3%.