Increasing Your Extract Efficiency
If you handed two identical sacks of ingredients to two all-grain brewers, and asked each to brew a 5-gallon (19-L) batch of beer, the resulting beers would likely differ in a variety of ways. Each brewer would be brewing with different water, different equipment and using different techniques. One potential difference between their beers would be a difference in the original gravities. If each sack contained, say, 10 lbs. (4.5 kg) of pale malt and 1.0 lb. (0.45 kg) of crystal malt, it’s possible that one brewer might yield 5.0 gallons (19 L) of wort at an original gravity of 1.048 (12 °Plato). The other might yield 5.0 gallons (19 L) at SG 1.060 (15 °Plato). This is because different homebrewers achieve different levels of extract efficiency. (In this case, the difference would be 60% vs. 75% efficiency.) Here are some ways to increase your extract efficiency and help you get the most from your malt.
Extract efficiency is essentially a measure of the amount of “stuff” you get out of your grains. This “stuff” is mostly carbohydrates. By dry weight, malt is 70–85% carbohydrate. Around 60% of the total dry weight of 2-row malts is starch. This starch is dissolved in the mash liquor and gets degraded into maltose and other sugars during the mash. However, there are other things present in malt that also end up in wort and contribute to its specific gravity. Malt contains proteins — between 9 and 12% for most 2-row malts — and mashing and lautering extracts some proteins, as well as polypeptides and amino acids resulting from the breakdown of these proteins. Other materials such as glucans, tannins and silicates are also extracted.
Brewers use the word “extract” to refer to all these various materials. “Extract” — the noun that refers to all the collective “stuff” that comes from your grains — should not be confused with malt extract (a condensed form of wort) or the verb “extract,” which means to take or draw out. Extract efficiency could thus be, somewhat confusingly, defined as, “the amount of extract you extract from your grains.”
If you rinsed all the materials that you possibly could from your malt, your extract efficiency would be 100%. In practice, however, brewers do not extract every last bit of soluble material. Comparing the actual amount of extract you get from your malt with the theoretical maximum gives you your extract efficiency. See the sidebar on page 48 for how to calculate this. Large commercial breweries typically achieve 90–98% efficiency. Any estimate of the average extract efficiency for homebrewers would just be a guess — but if I had to guess, I’d say 70–75%. (Brew Your Own recipes assume an extract efficiency of 65%.)
Achieving a high degree of extract efficiency is obviously a benefit — you’re getting more from your grain. And, there are many factors that influence extract efficiency. However, higher rates of extraction always come at a cost. These costs may be a longer brewday or lowered wort quality. Thus, brewers strive to achieve the best efficiency possible given the constraints of time and quality. In this article, I’ll describe how the average homebrewer can increase his or her extract efficiency without greatly extending their brewday or lowering their wort quality and what tools can help you reach your goal.
Crush
In order for malt to be successfully mashed, it needs to be crushed first. And for most homebrewers, the crush is the variable that they can most easily manipulate to increase their extract efficiency. Simply put, the finer the malt is crushed, the more extract can be yielded from it (assuming all other variables are equal.) However, overly fine crushes lead to a variety of problems.
As malt is crushed increasingly finely, lautering times will increase. The flow of liquid through the grain bed slows and may even stop. Below a certain size, husk particles will be too fine to provide a filter bed that is porous enough for the wort to be drained efficiently. Likewise, the more the husks are degraded, the more husk surface area is exposed to the mash and sparge water. As such, more tannins may be extracted from the husks.
So, in practice, a balance must be struck between the fineness of the crush and the ability to lauter the grain bed in a reasonable amount of time. And, of course, you also want your wort to be free of excessive tannins. As a rough guide, in well-crushed malt, the husks are usually broken into two or three pieces. The starchy interior of the malt should be reduced to roughly equal portions of flour, fine grits and coarse grits. A really good crush would consist of slightly more coarse grits and fine grits, and slightly flour than a strict 1⁄3 to 1⁄3 to 1⁄3 mix.
Learning what properly-crushed malt looks like takes a little experience, but this can easily be gained by examining your crush every brew and keeping track of your extract efficiency. However, even an inexperienced brewer can detect major problems. If you see uncrushed kernels and little or no flour, your mill gap is too wide. Conversely, if your crushed malt looks like it is half flour, all the husk particles are tiny and you experience slow (or stuck) lautering, your mill gap is too small.
The best way to take control of your crush is to adjust the gap on your malt mill. For homebrew two-roller malt mills, a gap of 0.045 inches (1.1 mm) is a common “all-purpose” setting that yields a good crush with most 2-row malts.
You can check the size of your mill gap by using a feeler gauge — available at most auto supply stores. The feeler gauge consists of a series of “plates,” each with a different thickness. To measure your mill gap, you see how many of these “plates” will fit in the gap, then total their thicknesses.
However, the look of your crushed malt is more important than the size of your mill gap. When milling your grain on brewday, run a pound or so of malt through, then examine the crush. If necessary, adjust the mill and crush another pound or two. Repeat until your crush looks good, then crush the rest of your malt. Many homebrewers, myself included, rely on a mill gap that works well in most situations and only adjust the mill if they see an obvious problem — for example, when milling wheat malt or thinner
6-row malts.
If you have a fixed gap mill or you get your malt crushed at your local homebrew shop, and it appears to be undercrushed, you can run the grains through the mill a second time. “Double milling” will reduce the average particle size in your crush, although it is not as effective as adjusting the mill gap appropriately. Homebrew shops don’t adjust their mill gap for every crush. Their mills should be set to a gap that will yield a good crush for most malts. However, with heavy use, this gap adjustment may change. If you get your grains milled at your local shop, check the crush before you leave the store.
Using uncrushed malt, you can get at least 35% extract efficiency. (Don’t ask me how I know this.) If you move from moderately undercrushed grain to an appropriately fine crush, your extract efficiency can easily increase by 10% or more.
Sparge Length
Once the crushed grains have been mashed and the first wort has been run off, the grain bed is rinsed with water (called sparge water) to recover extract that did not flow out with the first wort. The more sparge water is applied, the more extract will be rinsed from the grains. However, brewers quit sparging and collecting wort when recoverable extract is still present. There are a couple reasons for this.
For starters, the amount of extract recovered per unit of sparge water declines as more sparge water is used. Put more simply, the first gallon of sparge water is going to rinse out more extract than the second gallon and so on. In and of itself, this isn’t a drawback. However, excess water needs to be boiled away in order to hit your target volume and gravity and most brewers do not want to extend their boil time significantly to gain only one or two gravity points.
More importantly, the character of wort being run off changes as more sparge water is applied. As the runnings from the grain bed decrease in specific gravity, the pH of the wort rises. And, at higher pH values, tannins are extracted at higher rates. In excess, they cause astringency in beer. So, it is recommended that sparging be stopped when the pH of the final runnings rises to 5.8–6.0. (This usually corresponds with a specific gravity of 1.008–1.010, but can vary somewhat depending on the minerals dissolved in your water.)
The easiest way to measure the gravity of the wort as you run it off is to use a refractometer. With a refractometer, you only need a drop of wort and you can get a reading in a couple seconds. When using a hydrometer, you need to take a larger sample (at least 200 mL for most homebrew hydrometers) and cool it before you can take a reading. Alternately, you can take the reading hot and consult a temperature compensation chart.
Another way of looking at this is, for every unit of grain added to your mash tun, a certain volume of wort can be collected. If for example, you brewed two beers — one with 10 lbs. (4.5 kg) of grain and the other with 16 lbs. (7.3 kg) — the one with more grain would require more sparge water to be completely sparged (i.e. sparged to the point that only low-quality wort could be run off). On my system, 10 lbs. (4.5 kg) of grain would yield about 6.5 gallons (25 L) of wort while 16 lbs. (7.3 kg) would yield over 10 gallons (4.5 L). (I’m more concerned with astringency than efficiency, however, and you may be able to collect more.)
Of course, some homebrewers collect the same amount of wort for every grain bill — enough to yield the full wort volume after their boil. For example, the brewer may collect 6 to 7 gallons (23 to 26 kg) of wort and boil 60 to 90 minutes to hit a 5.0-gallon (19-L) target. This works well with average-strength beers, but extraction efficiency gets progressively worse for bigger and bigger beers. If, for example, I brewed a beer with 16 lbs. (7.3 kg) of grain, but stopped collecting wort at 7.0 gallons (26 kg), I would be leaving behind the extract that would have come with the final 3.0 gallons (11 L) of sparge water.
When brewing bigger beers, you need to decide if you want to maximize your efficiency by fully sparging your grain bed, or accept a lower efficiency. If you fully sparge the grain bed, your efficiency for your big beers will be the same as it is for your normal-strength beers. However, you will have to boil your wort longer to condense it. Conversely, if you collect only the amount needed for a 60–90 minute boil, you will be lowering your efficiency, but keeping your boil time down. To compensate for lower efficiency, you can add more malt to the grain bill or add malt extract to your boil.
The flip side of this argument is that you can easily oversparge your grain bed when brewing lower gravity beers. For example, when I brew 5.0 gallons (19 L) of bitter, my grain bill is usually around 7.0 lbs. (3.2 kg) with a target original gravity around 1.036. At 7.0 lbs. (3.2 kg), I can collect 4.5 gallons (17 L) of wort before I need to stop sparging. Thus, in order to reach my target pre-boil volume, I need to add water. If I collected 7.0 gallons (26 L), my efficiency would increase beyond what I normally get, but the beer would be excessively astringent. So, if you have been collecting enough wort for a full-wort boil on your weakest beers, and you have been encountering astringency, this may be the reason.
If you are a batch sparger, your kettle volume is determined by how much sparge water you add for the two (or three) sparges. Larger grain bills are going to force you to scale up the amount of sparge water (assuming you aim to equalize the volume of wort obtained in the first and second wort). You should experiment to find a total-liquor to grist ratio that works best with the beers you usually brew. For beers brewed with more or less grain, keep this ratio the same to preserve your rate of extract efficiency.
After the crush, completely sparging your grain bed is the variable that will be most helpful to most homebrewers looking to increase their efficiency. For brewers of big beers, it may be the most important variable if they are already getting a good crush.
Temperature
If you heat a thick sugar solution, it becomes less viscous. Heating the wort in your grain bed will likewise lower its viscosity and let it flow more freely. As such, the hotter your grain bed and sparge water are, the higher your extract efficiency. Once again, however, there are opposing considerations.
At some point during the mash, the temperature needs to be in a certain range (roughly 148–162 °F/64–72 °C) for starch conversion to occur. Afterwards, however, you could heat the grain bed to boiling temperatures and sparge with boiling water. If you did so, your extract efficiency would almost certainly exceed its present value (assuming everything else was the same). However, your beer would also be awful.
Heat not only lowers the viscosity of the wort, it increases the solubility of solids in it. Excess heat can leach undesirable compounds from the malt husks. This is especially true near the end of wort collection when the specific gravity of the runnings is low and the pH is high (relative to mash pH). Brewing scientists have determined that, at the end of wort collection, the temperature of the grain bed should not exceed 170 °F (77 °C).
For the homebrewer looking to increase his or her extract efficiency, there are a couple options for managing temperature during lautering. The standard recommendation is to perform a mash-out — heating the mash to 170 °F (77 °C) after starch conversion is complete — then sparge with water hot enough to maintain that temperature in the grain bed throughout wort collection. The key here is that it’s the temperature of the grain bed that matters, not the sparge water itself. When sparging, use a temperature probe to check a few places at the top of the grain bed every 5 minutes or so. Adjust the temperature of your sparge water so the top of the grain bed stays as close to 170 °F (77 °C) as you can manage, without going over.
Some homebrewers do not have the capability of heating their mash after conversion and do not have enough room in their mash tun to hold enough water to achieve a proper mash-out temperature. For example, if you are using a picnic cooler as a mash/lauter tun and it is almost full, you may not be able to do a mash-out. In that case, you still have one option. Heat your sparge water such that the grain bed temperature rises throughout wort collection. You will begin at mash temperatures — or whatever mash out temperature you can achieve. Sparge with water hot enough to raise the temperature of the mash progressively as you sparge, letting the grain bed temperature settle into 170 °F (77 °C) near the end of wort collection. Finding the proper sparge water temperature will take some experimentation on your part. The rate of heat loss from the lauter tun, the rate at which you add sparge water and amount of time you collect wort over will all play a role. (When I’ve done this, I’ve started with sparge water heated to about 190–195 °F/88–91 °C.) Note that, if the grain bed temperature quickly increases to 170 °F (77 °C), you can add room temperature water to your hot liquor tank to lower the temperature to 170 °F (77 °C). Then simply keep sparging to maintain the grain bed temperature at 170 °F (77 °C).
Time
The last of the major factors affecting extract efficiency is time. The longer your sparge water is in contact with the grain bed, the higher your efficiency (assuming all other things are equal). However, as with the amount of water you add, there are decreasing returns with longer and longer lautering times. In a commercial brewery, lautering generally takes about 120 minutes when a mash tun is used (as opposed to 60–90 minutes when a mash filter is used). The grain bed depth in most homebrew lauter tuns is less than that in most commercial breweries — 3–4 ft. (0.9–1.2 m) is common, but deeper vessels are not unheard of. Correspondingly, most homebrewers (who use continuous sparging) spend about 60–90 minutes lautering their grain bed.
At the homebrew scale, one problem with extending lauter times is heat loss. The relatively small volumes of grain we use means that the volume of the grain bed is fairly small, has a comparatively large surface to volume ratio and thus loses heat fairly quickly. Although many homebrew mash tuns can easily keep temperatures at 170 °F (77 °C) for 60–90 minutes (with the appropriately heated sparge water), extending this to two or more hours might be difficult. With a slow enough sparge, it might be possible for the top of the grain bed to be hot while the bottom is relatively cool. If this were the case, a faster, hotter runoff would likely yield better efficiency.
While mashing, you can calculate the total volume of wort you will collect. If you know how long you want your sparge to last, just divide the total volume (in gallons, quarts or liters) by the time of the sparge (in minutes). This will tell you how fast you should collect your wort (in those units per minute). If you collect wort at a constant rate, even for brews with different sized grain bills, you will take longer to collect the wort for big beers than for small. This isn’t wrong, but you might gain a couple of gravity points on your smallest session beers, and save a little time on your biggest barleywines, if you adjust your wort collection rate to keep your total lautering time constant.
Of all the variables presented so far, time spent lautering is going to mean the least. Anecdotal evidence suggests that quick lauters — with total times of 30–45 minutes — don’t cause extract efficiency to drop precipitously. If you’re trying to add a couple points to your beers, you’ll want to take the time here. If your time is more important than a half pound of malt, you might consider speeding up your wort collection.
When batch sparging, wort collection proceeds much more quickly because sparge water is actively stirred into the grain bed once or twice. And, once stirred, all the wort in the vessel is of a constant volume. Hence, the sparge water is not going to dissolve more extract with longer contact times. Standard batch sparge practice is to drain the mash/lauter tun as quickly as the grain bed and equipment will allow.
Minor Factors
Many other factors affect extract efficiency, including stirring the mash and the design of your lauter tun. (See the March-April 2007 issue for more on lauter tun design.) Stirring can help if your malt is undercrushed or your mash time is short. However, you may also lose a significant amount of heat when you open up your vessel to stir it. With a good crush and a 60–90 minute mash, stirring is not likely to cause much of a gain in efficiency.
Your mash temperature and water chemistry also matter, but the values for best efficiency — 149–154 °F (65-68 °C) at a pH of 5.2–5.4 — overlap the range required for the enzymes to do their work. (The basic connection here is that a maltose solution is less viscous than a starch solution at the same temperature.)
Finally, the German author Kunze states that the highest extract efficiency comes from adding your sparge water in three to four additions rather than continuously. To see a difference due to this, however, your extract efficiency would likely need to be very high already.
Calculating Extract Efficiency
What’s the easiest way to calculate your extract efficiency? Let someone else do it. Most homebrew recipe calculators will give you an extract efficiency based on your recipe, batch volume and actual original gravity (OG). (On some, you may have to enter the recipe and adjust the extract efficiency until the projected OG matches your actual OG.)
To calculate it by hand, you need to to know a few different values — the weight and extract potential of each grain, adjunct and sugar in your recipe, your wort volume and your original gravity. The formula is:
Extract Efficiency = OG * Volume Weight * Extract Potential
where OG is original gravity in “gravity points” or GP (i.e. a wort with a specific gravity of 1.052 has 52 GP); Volume is given in gallons; Weight is given in pounds and Extract Potential is given in GP per pound (for example, if a pound pale malt yields a wort with maximum OG of 1.037, its Extract Potential would be 37.
Note that, in order to get a meaningful value from this equation, the numbers you plug into the formula need to be meaningful. If you can’t accurately measure the weight of your grain or the volume or original gravity of your wort, the number you get from this formula will be useless. If you haven’t already calibrated your fermentation buckets or carboys, you should if you plan on trying to increase your extract efficiency.
Is My Efficiency OK?
Many homebrewers ask, is my efficiency OK? Here is my suggested test: go pour yourself one of your homebrews and taste it. Does it taste good? Did you have fun brewing it? Then your efficiency is probably OK.
Another way to look at the issue would be to ask, are there any beer styles that require a high efficiency to be brewed correctly and taste right? The short answer here is “no.” There is no readily identifiable flavor or aroma that comes with higher extract efficiencies. If you tasted two pale ales — one brewed with 70% extract efficiency and the other with 80% — it’s unlikely you could tell any difference, provided the amount of malt in the grain bill was adjusted so that the original gravities were the same (and all the other relevant variables were held to be the same).
I do think that some beer styles — especially lagers brewed mostly from malty base malts (such as Vienna and Munich malt) — taste best when they have a grainy/husky flavor that falls just short of astringent. This character comes from sparging right up to the point of disaster. As such, beers brewed this way tend to show fairly high efficiencies. But, it’s really the sparging, not the efficiency per se, that yields this character. (Water chemistry plays a role here, too.)
This is not to say that extract efficiency is irrelevant. Better extract efficiency leads to lower grain costs — although, at a homebrew scale, this difference may be trivial. More importantly for many homebrewers, better extract efficiency makes it easier to produce big beers. If you get a good extract efficiency, you can fill your mash tun to the brim and get a bigger beer than if your extract efficiency is poor. A big hint when making high-gravity beers is to keep your mash thickness relatively dense (about 1 qt/lb. or 2 L/kg), stir the mash frequently if you can do so without losing heat, then sparge as slowly as is feasible with water that keeps that grain bed at 170 °F (77 °C). Look for a point to cutoff sparging that represents a good tradeoff between efficiency and boil length for you. Also, if you are going to need an extended boil to bring your volume down, bring the wort to boil while wort collection is still proceeding. This will save time overall in the brewday.
Conclusions
So, if you are looking to maximize your extract efficiency, here is an approach that will likely be fruitful:
First, take a look at your crush. If you think you could crush a little more finely, try it. If you get better efficiency and have no problems lautering, try crushing a little finer next time. Keep adjusting your grain mill until you reach an acceptable tradeoff between extract efficiency and ease of lautering. (And keep some rice hulls on hand in case your mash does set up.)
Measure the temperature of your grain bed, not your sparge water, as you lauter. Check the bed in a few places every 5 minutes or so and boost the temperature of your sparge water if the grain bed temperature falls.
Add enough sparge water to fully rinse the grain bed. (Note: you can heat the wort in your kettle as you collect it, so that the boil can start as soon as the full volume had been collected.) Most homebrewers should yield at least 1 gallon of wort from every two pounds of grain (~4 L/kg), and probably more — up to perhaps 1.5 gallons per 2 lbs of grain (~6 L/kg), but you’ll need to determine this value for yourself in your own brewery. Collecting this wort over 60–90 minutes is a good compromise between time and efficiency, although cutting the time to 45 minutes will likely only drop your efficiency a little bit.
Achieving very high extract efficiency requires getting all of your “ducks in a row.” Conversely, if your efficiency is markedly low, it is most likely because of a single factor (rather than a conglomeration of many factors). The good news is, if you can identify that key factor, your efficiency can rise by fixing it. (The even better news may be that the variable is most often the crush.)
