Calculating Brewhouse Efficiency
To put it crudely, brewhouse efficiency is a measure of what you get instead of what you could get from your grain. And we are talking about grain mashing here, since if you use malt extract the mashing bit has been done for you. For example, most pale malts will give an extract yield of about 80% (see later) of their weight, the remainder being husk material and protein. But this is only under ideal conditions in the laboratory; that is using a very fine grind of the malt and using an excess of sparge water to ensure all the extract is recovered. In practice, craft and homebrewers use a coarser grind and limit the amount of sparge water so as to avoid extraction of unwanted materials such as tannins. So nobody gets all that 80% and what they actually get as a ratio of what they could get is called brewhouse efficiency.
What brewers will get is anywhere from 80-95% of the theoretical yield. Does that matter to the homebrewer so long as he or she is still brewing good beer? Yes it does, because if you are designing a recipe you have to be able to make it so that you hit your target gravity. If you are using someone else’s recipe you need to know the basis on which the recipe was designed and adjust it to your own brewhouse efficiency. For example, BYO uses a standard of 65% efficiency in published recipes; if you want to brew your version and your extract efficiency is, say, 70% then you would need less malt than is given in the BYO recipe. So let’s see how you work out what your extract efficiency is.
Calculating Extract Efficiency
Perhaps the best and most scientifically proper way to do this is to use the metric system, with gravities measured in degrees Plato, as was demonstrated in the October 2003 column of “Mr. Wizard.” But, I am going to assume that not all Americans are familiar with the metric system, so I will work with specific gravity, pounds, and gallons. The first thing we need to know is the maximum yield that can be obtained with the grains we are going to use. Homebrew suppliers rarely give this figure, but you could go to the maltster’s website for it. An easier way is to go to the BYO website where there is a grains and adjuncts chart that gives these numbers (www.byo.com/resources/grains).
So let’s start with a simple example — a pale ale brew using only 2-row pale malt as base. The BYO chart says this should give a gravity of 1.037 for 1 lb. (0.45 kg) in 1 gallon (4 L) of wort. So let’s say you used 10 lbs. (4.5 kg) of this malt in a 5-gallon (19 L) brew and got an original gravity (OG) of 1.050, so the total gravity points (GP) you got was 5 x 50 = 250 (volume x OG). Now, what you could have got at a maximum was 10 x 37 = 370 GP (weight x gravity). And your extract efficiency was = (250/370) x 100 = 68%.
Once you have done this you can then go the other way and say how much malt do I need to brew 5 gallons (19 L) of beer at an OG of 1.056 when my efficiency is 68%? Then we want
5 x 56 = 280 GP. The maximum yield we can get from W lbs. of malt is W x 37 GP. Then:
(280 x 100)/(W x 37) = 68, and W = (280 x 100)/37 x 68 = 11.1 lbs. malt
Note that the chart gives a range of 1.037-1.038 and I have taken the lower figure simply because I had to choose one. If I had taken the higher figure the efficiency would have come down to 66%, and the amount of malt required in the second example would have been 11.2 lbs., a relatively trivial difference.
Now, I gave a simple example with only one malt, so what happens when other malts go to make up the grist? Well the calculation does become a little more complicated because specialty malts have maximum yields different from those of base malts, as you can see from the BYO chart. So let’s say we brewed 5 gallons (19 L) of porter as follows:
8 lbs. 2-row pale malt (max. yield 1.037/lb./gallon)
1 lb. crystal malt (60 °L) (max. yield 1.033/lb./gallon)
0.5 lb. Victory® malt (max. yield 1.034/lb./gallon)
0.25 lb. chocolate malt (max. yield 1.034lb./gallon)
Then our maximum yield would be:
(8 x 37) + (1 x 33) + (0.5 x 34) + (0.25 x 34) = 355 GP
Say we got an OG of 1.048, giving a total of 48 x 5 = 240 GP
So our efficiency = (240/355) x 100 = 68%
Once you have calculated your efficiency you can, as I showed earlier, use this number to work out other recipes. However, there are some limitations and this number can change according to a number of factors, such as milling, changing mash systems, radically altering mash temperatures, or even if you go to a much higher amount of grain to brew a beer of significantly higher OG. For these reasons and as a troubleshooting guide it is a good idea to calculate brewing efficiency on a regular basis.
Improving Brewing Efficiency
Milling — So you listened to me, calculated the number and you found that you had a low efficiency and want to improve it. The first question is where are you losing out on yield? The answer is mostly in mashing and sparging. The only other likely loss is with the trub after boiling, but this is generally fairly trivial. If you suspect it, then “whirlpooling” by rapid stirring before wort separation will help, as will using high alpha acid hops for bittering, so as to limit the trub.
The potential problems in mashing start with the grind, which is “myspeak” for milling. If the milled grain is too fine and floury you may lose extract through clogging of the mash, which causes poor drainage and results in the hold up and loss of wort. In the extreme the result will be the dreaded stuck mash, which is about as inefficient of a situation as you can get. A lesser problem is the formation of channels through the bed, which reduces the ability of the sparge water to leach out wort.
If the grain is ground too coarsely, the reverse occurs and the sparge water will go through the bed too quickly without properly eluting wort from the grain bed. A coarse grind will often result in poor contact between the mash water and the interior of the grains, which again means loss of sugar and flavor extracted from the grains. This is especially true if there are a lot of unbroken kernels. In fact, this can actually be a worse problem in terms of efficiency than having the malt too fine.
So check your mill by taking a sample of the ground grains and looking to see that all of them are broken, but that a good part of the husks remain intact. If this gives unsatisfactory results in terms of your brewhouse efficiency just close the gap between the rollers a little for the next brew. The finer you can mill the grain without getting to the problems described earlier the better your extraction and the efficiency of your system will be.
A few other points about milling, the first being that specialty malts should be ground more coarsely than base malts. Since they are all roasted to one extent or another these malts can easily crumble and form very fine flour if your mill’s rollers are too tight. If you buy your grain pre-ground, don’t be afraid to speak to your supplier if you are unhappy with the results that you are getting. We buy pre-ground grain at BruRm@BAR in New Haven, Connecticut and had a yield problem with it that was only cured by visiting the supplier and standing over the mill operator as the grain was ground! And finally, if you buy malt this way do not see it as a saving to buy large amounts if much of that grain is going to sit around for more than 3-4 months. That’s a good way for the ground grain to pick up moisture and go “slack,” resulting in a loss of yield and a fall in efficiency.
Mashing — It is perhaps obvious, yet worth repeating that to be efficient you must mash under the proper conditions. Generally you should keep a mash at temperatures between 148–158 °F (64.4–70 °C), depending upon the degree of fermentability you want to achieve. Temperatures outside this range will result in a loss of extract through incomplete conversion. You should also check mash pH and ensure that it is between 5.2–5.4. If it is not then you need to treat your brewing water appropriately. And if you do not have a pH meter I advise you to buy one — remember you are trying to improve brewhouse efficiency so this small investment can pay big dividends!
Another point in achieving high extraction is that of mash consistency, that is the malt to water ratio. The ratio often recommended for homebrewers is one quart of water per pound (1 L/0.45 kg) of malt, which makes for a thick mash. This results in optimum conditions for enzymes, protecting them from denaturing and allowing alpha- and beta-amylase to work as a team and to produce a good balance between fermentable sugars and dextrins. However, a thick mash can reduce yield (which we are trying to improve!) because they can limit the amount of starch that can be solubilized due to the high concentration of starch breakdown products. Thick mashes can also inhibit the actions of other enzymes, such as proteases, and they can result in temperature differentials in the grain bed. This is particularly true in homebrewing where mixing of the grain and hot water in a thick mash is often inefficient. Mixing during mashing is a way out of this last problem, but I’ll discuss that later.
One obvious way out of these problems is to use a more dilute mash, and this is the way to go if you are dissatisfied with your yield and hence brewhouse efficiency. You do not want to dilute too much, since in thin mashes the starch-degrading enzymes rapidly denature, especially beta-amylase, and that will give a wort with low fermentability. What you want to do is to work in the range 1.2–1.6 qts water per lb. (1.1–1.5 L/0.45 kg) of grain. In a straight infusion mash this will be thick enough to keep the enzymes active long enough to do their job and will allow take-up and degradation of pretty much all of the starch in the grain. It will also help ensure good manual mixing and therefore full contact of grain and water in a simple homebrewing set up, and hence of a uniform temperature throughout the mash. This last point is also important if you are doing a multi-temperature step mash, where efficient mixing at every step is essential to achieve more or less uniform temperature in the mash. In either case you should find you have achieved an increase in brewhouse efficiency. For reference I usually work at 1.2 qt. per lb. (1.1 L/0.45 kg) of grain.
Mash Mixing — It would seem to be a good idea to use a mixer and continuously stir the mash. Many commercial brewers do exactly that for it ensures good heat transfer and uniform temperatures in the mash, and always results in an improvement in extract yield. If you are contemplating this you will need a low-shear mixer so you do not break up the grain, which will cause wort runoff problems. For instructions to build a mixer from an old ice-cream machine, check out “Build a Better Mash Tun” in the May-June 2013 BYO. Further, professional brewers who use a mash mixer regard it as essential to have a separate lauter tun for wort run off and sparging. The idea is that running off directly from the mash tun will be a slow and inefficient process. However, I do have a mash mixer and I do run off directly from the mash tun without any problem — for a 5-gallon (19-L) brew I can complete run and sparging in 30 minutes, with good extract yield. Note also that RIMS (recirculating immersion mash system) and HERMS (heat exchange recirculating mash system) effectively mix the mash by means of continuous recirculation of wort.
Finale
Calculating brewhouse efficiency is a relatively simple exercise but one that will help you to improve both the quality and the consistency of your beer. If you do not like “number crunching” use a spreadsheet; either devise your own, or buy one of the several brewing programs available. Either way, you want to know your brewhouse efficiency in order to be the best brewer you can be.
