SUMMARY
Knowing your brew house efficiency is important when creating recipes. Brew house efficiency takes into account all facets of the brewing process; mash, boil, transport to fermentor, etc). An incorrect efficiency will make it difficult to achieve the proper OG targets and can lead to inferior beer. So bust out your algebra shoes and dust of you calculator gloves, we've got math to solve.
EQUATIONS & VARIABLES
OG - Original Gravity (post-boil)
Wg - Weight of Grain (lbs)
Vb - Volume of Batch (gallons)
PPG - Actual Points per Pound per Gallon (efficiency)
PPG' - Theoretical PPG (represents 100% efficiency)
Eff - Brew House Efficiency
PPG = Vb * (OG-1) * 1000 / Wg
Eff = PPG / PPG' * 100%
In terms of PPG, 30 is the universal target. However, different malts provide different amounts of sugar, so PPG will vary from recipe to recipe. However, mash efficiency will remain the same (provided the same mashing technique and equipment). To actually calculate mashing efficiency, we need to compare actual PPG to the theoretical (or max) PPG for our given recipe. For quick calculations you can use 38ppg as a base (since 2-Row malt has a max PPG of 38). So if your system yields 30 PPG, then you have a rough efficiency of 79% (=30/38). For more detailed calculations you need to calculate the sugar contributions of each grain.
PPG' = (PPGa * Wa + PPGb * Wb + PPBc * Wc...) / Vb
where PPGa = Max PPG for Grain A (PPGb for Grain B, etc) & Wa = Weight of Grain A in recipe (Wb for Grain B, etc)
So using an example from my recipe list, we can calculate PPG' for Ember, a Smoked Amber. Max PPG values from beersmith (PPG = SG -1).
9.0lbs Pale Malt (38 = max PPG)
1.0lbs Smoked Malt (34 = max PPG)
1.0lbs Crystal 80 (33 = max PPG)
.50lbs Crystal 60 (33 = max PPG)
PPG for Ember = 6 * (1 - 1.058) * 1000 / 11.5 = 30.3
PPG' for Ember = (38 * 9.0 + 34 * 1.0 + 33 * 1.0 + 33 * 0.5) / 6 = 70.9
Eff for Ember = 30.3 / 70.9 * 100% = 42.7%
*Note: You can also use the above equations to calculate mash efficiency. To do so, use pre-boil values for OG and Vb. That way you can scrutinize your mash procedure, which is where a majority of efficiency losses take place.
IMPROVING EFFICIENCY
Yikes! That 42.7% was pretty low, but after some research I have identified several ways to rectify the issue.
- Mash Tun: Increase your water to grain ratio from the standard 1.25qt/lb and try 1.5 or even 2.0qt/lb. Some homebrewers have increased efficiency by 15% by this method alone
- Sparge Hot: Before you drain your mash tun, take some time to really boost the temperature. Adding hot water, or directly heating the mash tun, will help the sticky wort flow freely. 168°F is the ideal mash temp for lautering.
- Lauter Slow: When lautering, instead of letting the wort flow quickly out of the mash tun, restrict it a bit and allow your sparge water to properly extract the sugars in your grain bed. A good rate is about 1 gallon of wort every 5+ minutes.
USEFUL SITES
There are several homebrewers with more experience and knowledge that myself. For more information and useful tools check out their websites
How To Brew by John Palmer - Mash Efficiency: this book has everything a homebrewer would want, and luckily for us it available online for free
Brewer's Friend: this website can help you calculate your efficiency and then uses it to directly influence your recipes. Super useful recipe creation tool.
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