Your grandmother may be able to get away with estimating measurements for her famous marinara sauce, but when it comes time to bake a cake, you can almost guarantee that she measures everything out with some precision. That’s because baking is more sensitive to proportions and process than other forms of cooking.
And just as we standardize cake recipes using conventions such as tablespoons, cups, and kilograms, we also standardize beer recipes. Process is, however, not generally replicable, which means that each brewer has to make adjustments according to the strengths and limitations of his or her own system.
One of the parameters that’s different for every brewer is efficiency. Further complicating the matter is that there are several kinds of efficiency. At their core, all forms of efficiency quantify how much sugar you get out of your grain, relative to how much is actually there for the taking.
In a Perfect World
Before you can calculate any kind of efficiency, you need to know how much potential there is in your mash. This is the easiest part because most malts have published gravity potentials, usually expressed as points per pound per gallon (ppg). A typical base malt might come in at 1.035 to 1.038 ppg, which means that at 100 percent efficiency, one pound of that grain in a one gallon batch would yield wort with a specific gravity of 1.035 to 1.038.
For a homebrewer making five gallons at a time, those gravity points get spread out over the entire batch, which means that one pound of the grain above contributes (at 100 percent efficiency) 1.007 to 1.0076 gravity points to the entire batch. To estimate the maximum theoretical original gravity for a given recipe, then, you simply sum all of the individual contributions from each grain.
Once you know the theoretical maximum for 100 percent efficiency, than you can adjust the original gravity according to your brewery’s own performance.
Mash Efficiency
Mash efficiency, or extract efficiency, refers to how much of the available starch in the grist actually gets converted to sugar. This number is largely related to mash chemistry and is affected by many factors, including
- Grist-to-water ratio
- Grist composition
- Mash pH
- Mash water composition
- Mash schedule (temperatures and rest durations)
Calculating extract efficiency is complex and generally impractical for most of us, especially since each grist is going to be a little bit different. Instead, simply understanding the effects of each factor on starch conversion can help you diagnose efficiency issues.
Grist-to-water ratio: Thinner mashes tend to convert more readily than thicker ones.
Grist composition: Adjunct-rich mashes and those with lots of Vienna and Munich malts might not convert as readily as one based mostly on Pilsner or pale malt.
Mash pH: Starch conversion typically works best when the mash pH is roughly 5.4 or slightly higher.
Mash water composition: Very hard or very soft water may require some adjustments, depending upon the mash, to achieve the desired mash pH.
Mash schedule: Longer rests and higher temperatures promote faster conversion than shorter rests and lower temperatures. Decoction also tends to improve mash efficiency.
Once grain starches have been converted, the next step in the efficiency game is ensuring that as many sugars as possible end up in the boil kettle. Which brings us to…
Lautering Efficiency
Lautering efficiency quantifies what fraction of the available mash sugars make it into the boil kettle. You can have the most efficient mash in the world, but it’s of little use if most of the sugars remain stuck in the grain bed. Lautering efficiency, then, depends on your specific lauter tun geometry (false bottom, manifold, braid, etc.) and the manner in which you sparge, typically continuous sparging or batch sparging. Again, this is a number that can be difficult to compute.
Large grists can dramatically reduce your lautering efficiency because they need more mash water, leaving less available for sparging. One way around this is to sparge to a larger pre-boil volume and extend the boil to evaporate the extra water and concentrate the wort, but this risks darkening the wort and caramelizing sugars in the kettle. Fortunately, this is often desirable in big beers!
Total Efficiency
Total efficiency, or brewhouse efficiency, is a measure of your overall grain-to-fermentor performance, and it’s the most important number for homebrewers to know. Total efficiency includes all of the effects of mash and lauter efficiency, as well as such things as hops absorption, dead space in the kettle, losses to the wort chiller, and so on. It’s the final measure of how many of those available starches ultimately get converted to sugars and survive the journey to your fermentation vessel.
In the example above, in which one pound of grain yields one gallon of 1.035 wort at 100 percent efficiency, a brewhouse efficiency of 70 percent would instead yield one gallon of wort with a gravity of 1.0245 (70% of 35 is 24.5). It doesn’t matter whether the efficiency drop was in the mash, the sparge, or somewhere else, all you care about is that the final wort represents 70 percent of the original potential.
The total efficiency is the number you most commonly tweak when adjusting recipes. Most of our recipes at Craft Beer & Brewing are standardized to yield 5.25 gallons (19.9 liters) into the fermentor at 72 percent total efficiency (we assume that 0.25 gallons/0.95 liters are lost to yeast and trub after fermentation, so you end up with 5 gallons/19 liters actually bottled or kegged). If your system is_ reliably _more or less efficient than that, then you would want to adjust the recipe accordingly. In most cases, you need only adjust the base malts, as specialty malts supply comparatively fewer fermentable sugars than, say, Pils or pale.
Finally, remember that the most important thing about efficiency isn’t getting a high number. It’s about getting a reliable, predictable number. Fortunately, brewing software such as BeerSmith makes this a piece of cake, and investing in a good calculator is one of the best ways to build consistency into your brew day.