After John got his new mill he began to wonder what other advantages having a mill would deliver, aside from crushing grain. That leads us to a discussion on mash efficiency, what it is and roughly how you calculate it.
Every grain has a theoretical maximum amount of sugar (post a saccharin conversion from starch) that it will yield. Brewing chemists and maltsters have devised a test that involves completely crushing malt into powder and seeing how much sugar it will yield. For the homebrewer, the expectation of that level of yield is unrealistic. Primarily because we don’t crush our grain into super fine powder and get 100% access to the starch and enzymes. We need to retain some structure to the malt in order to create a filtering mash bed in the form of good husk material. A good mill attempts to deliver great starch access while preserving malt kernel structures that assist in lautering.
There in we have the loss of 100% sugar recovery from the “ideal” lab standard. The difference between what the lab gets and what you get from your mash tun post lauter is often converted to a ratio, and expressed as a percent. On average 70-75% is a very good mash efficiency. More efficiency in your system means you need less grain to get the same OG from a recipe written with a lower efficiency. Often magazine articles are written with a lower efficiency than what we call ‘average’. I am not sure why this is, perhaps its historical.
Why do you want to care about efficiency? Well primarily its necessary for us as brewers to communicate recipes back and forth. If your process yields a much higher efficiency than mine your recipe will be out of balance. This becomes big issue when a recipe must be balanced against the IBUs. Think of producing an IPA at 1.065OG with 65IBUs. That balance between bitterness and gravity will be way off if you end up only getting an OG of 1.045 and still use enough hops for 65 IBUs.
There are some cost savings as well. Large commercial breweries strive for very high efficiency because when hundreds of pounds of grain are being mashed every little bit helps the bottom line of the batch. 10% of that size a batch can mean a lot of cost savings. On the homebrew scale if you were to jump from 70% efficiency to 80% efficiency its like saving 10% in grain.
Lastly, efficiency gets a lot of attention sometimes in this male dominated hobby. Bettering each other in efficiency is like a pissing match of maleness sometimes. The important thing is that increase efficiencies often come at a price. Some brewers report a loss in overall richness or fullness from a malt bill when the efficiency gets close to 85% or more. This isn’t well understood quantitatively but from a qualitative side is seems right to me. Higher efficiency often means more water in the sparge, which means more tannin and other flavors. An interesting way to see what I mean is to do a batch sparge. Save a little first runnings and take the gravity. Then measure the gravity of your second runnings. Dilute your first runnings down to match the gravity of the second and do a side by side taste test. The first runnings do taste more maltier despite being at the same gravity. There is something about the desirable malt flavors that we like that seem to concentrate in those early runnings. The same holds ups with fly sparging.
We don’t talk about how to adjust your efficiency here perhaps that best for a second post. But if you want help on how to work with gravity points and scaling the sugars in your recipes check out this old post of ours on working with malt PPG.