In the previous installment of Techniques, I discussed aspects of the mash that you could tweak once you have learned the basic skills of mashing.

In this installment, I continue the discussion and look at lautering speed, mash thickness and mashing times. I’ll also discuss a finer point regarding extract efficiency.

Lautering speed

In a fly sparged (or continuously sparged) homebrew set-up, the speed of wort collection is inversely related to extract efficiency — the faster you go, the more inefficient you are. Excessively fast wort collection can also compact the grain bed, slowing or even stopping wort collection. This is the dreaded “stuck mash.”

In a commercial brewery, brewers want to rinse their grain bed (sparge) and extract as much from their grain as is practical. There is a point at which a slower runoff could yield more extract, but it would cost too much in terms of time spent. For homebrewers, a total wort collection time of around 60–90 minutes has two main benefits. First, you get a thorough rinsing of the grain bed. Second, at this speed, the chances of encountering a stuck mash are very slim, even when working with wheat or rye.

In no-sparge or batch sparge mashing, there is no connection between run-off speed and efficiency. When using these techniques, the wort you run off is all of the same specific gravity and you should drain your mash tun as fast as you can manage. Likewise, if you performed a thin mash, you may choose to run off a bit of first wort before you begin sparging. This first wort can be run off quickly without any loss of efficiency.

Mash thickness

In the previous article, I discussed how mash thickness affected temperature differences across the grain bed. In thicker mashes, grain solids can insulate “pockets” of hot or cold mash better. 

Mash thickness also affects fermentability. Worts produced from thinner mashes are more fermentable than worts from thicker mashes if all other variables are equal. Of course, the temperature of your saccharification rest primarily determines fermentability and most homebrewers choose a standard mash thickness, often based on how much liquid their mash tun can hold. In contrast, some commercial brewers vary their mash thickness according to beer style. For instance, in Germany, Munich-style lagers are typically made with a thick mash while Pilsners are made from a thinner mash.

When performing a step mash and using hot water to increase the temperature between rests, your mash gets thinner and thinner. While it is unusual for the mash to get too thin for conversion to take place, homebrewers frequently encounter problems with their mash volume. Many have ended up with a full mash vessel, yet are still several degrees below their target temperature. Two solutions to this problem are to mash in your kettle and use direct heat to change the mash temperature or to employ a decoction mash. In any step mash where hot water infusions are used, it pays to mash in thickly, so the mash doesn’t get too diluted by the time you are ready to mash out.

The overall range of usable mash thickness ranges from roughly 2:1 (kg water: kg grain) to 5:1. In the units homebrewers use most this is roughly 1 quart of water per pound of grain (qts./lb.) to 2.5 qts./lb.

Mashing times

The amount of time spent mashing has received little attention in the homebrew literature. Most recipes for single infusion mashed beers specify to mash for an hour. Step or ramped mashes may be longer.

As long as your mash temperature stays in the beta-amylase (or maltose-producing) range, increasing your mash time increases fermentability. For brewers of extremely fermentable beers, rests in or ramps through the 131–145 °F (55–63 °C) range may last for hours. Bud Light, for example, achieves its high fermentability not through the addition of enzymes, but through a 3.5-hour mash around 140 °F (60 °C). Once you move the temperature into the high alpha-amylase range, most enzyme activity will stop shortly and extending the mashing time at these temperatures has little effect.

The amount of time spent at a beta-amylase rest may need to be shortened, however, if enzyme right (or “hot”) malts are used. Some 6-row barley malts have so much enzymatic power that brewers of American Pilsners and light beers must shorten their mash times or face overly fermentable worts.

An underappreciated aspect of mashing times is that longer mashing times allow for more contact time with the husks, from which malty flavors — but also tannic and other off flavors —are derived. I spoke with one brewer,  who requested anonymity, who got rid of a hard-to-peg off-flavor in his Pilsner by getting rid of some low temperature rests and shortening his mash schedule. (His wort fermentability, incidentally, remain-ed unchanged.)

You can experiment with increasing your mashing time at “low” temperatures to increase fermentability, but some commercial brewers have gone the other way and tried very short hot mashes. One brewery has even gone to a short single infusion mash at 165 °F (74 °C)! For the adventurous homebrewer, experimenting with odd mashing schedules could yield interesting results.

A note on extract efficiency

At some point, most advanced all-grain brewers attempt to calculate their extract efficiencies — the percentage of extract they get from their grains, compared to the theoretical maximum.  The numbers you need to plug into this calculation are your original gravity, weight of your ingredients, potential extract of your ingredients and wort volume. If you plug these numbers into your brewing software or spreadsheet, your computer will spit back a number, expressed to however many decimal points your display typically shows. For an example, let’s say the your calculated efficiency is 75.86439. What do these digits mean? An underappreciated fact is that, unless you made careful measurements of all the variables, all of the digits expressed in this extract efficiency — with the exception of the “7” and possibly the “5” — are meaningless. Let me explain.

When you perform a calculation using measured variables, the answer you get cannot be more precise than your measurements themselves. For example, let’s say you live in a town that is serviced by two highways — one runs exactly north/south and the other runs exactly east/west. Both highways meet in the center of town. Let’s further say that there are two homebrew shops outside of town. One is 5.2 kilometers (km) north of where the highways cross, as measured by your car’s odometer; the other is 3.7 km west. How far apart are these shops as the crow flies? If you remember the good old Pythagorean Theorem, you can quickly calculate that they are 6.382005 km apart. However, most of the digits expressed in this answer are useless. Your car’s odometer only measured the distance to the nearest tenth of a kilometer, yet the answer is expressed to a precision of a millimeter. In reality, the best answer is that the two shops are 6.4 km apart. And, given that the “4” is the last significant digit in this number, the best way to interpret this number is look at it as a range of numbers from 6.35 to 6.44 — all the numbers that would round to 6.4.

Before we take this highway all the way to Dorksylvania, let me explain what this has to do with extract efficiency. When calculating extract efficiency, you can only usefully express your answer to the precision that your measurements were taken. For example, if you want to express your extract efficiency to two digits — say 75% — all of your measurements have to be taken to two significant digits. To be specific, you’d need to take your OG to two “gravity points.” This is not a big problem; most homebrewers give their specific gravity as 1.0XX, where XX are two digits that they actually measure with their hydrometer.

Next, you’d need to have measured your weight to two significant digits. For a 5-gallon (19-L), batch this would most likely mean your grains measured to the nearest XX lbs. (or Y.Y kg) — in other words, to the nearest pound or tenth of a kilogram. Again, no sweat. Your potential extract value should likewise be expressed to two significant digits.

However, you’d also need to measure your volume to two significant digits. At a 5-gallon (19-L) scale, this would mean volume measured as X.X gallons (or YY L) — in other words, the volume measured to the nearest tenth of a gallon (about 13 fluid oz.) or to the nearest liter. (Note that the precision required varies with scale. For a 15-gallon (57 L) batch, you’d only need to measure to the nearest gallon to get two significant digits.) This is where the calculation may break down for many homebrewers. Unless you’ve actually calibrated your fermenter, you are just assuming you have 5 gallons (19 L) in it. Without actually measuring (and assuming you really are within a half gallon (1.9 L) of the 5-gallon (19-L) mark), you can only meaningfully express your extract efficiency to one significant digit. In our case a calculated 75.86439 would round to 80%. (This may sound like your efficiency went up, but it didn’t. In this example, the zero in “80” isn’t significant, so this single number really represents a range from 75–84, the range of numbers that would round to “80.”)

If you wanted to express your extract efficiency to 3 significant figures, notice that your job becomes a lot more difficult. You need to measure your gravity to 1.0XXX. In other words, you might have to estimate where, for example, you are between SG 1.048 and 1.049 on your hydrometer. Likewise, you’d need your weight measured as XX.X lbs. (or Y.YY kg), roughly to the nearest 2 oz. (or 10 g). This would be your easiest task in this case. For potential extract, you’d really need to get a malt specification sheet, as specs vary enough that the third significant digit would need to be measured. You couldn’t rely, for example, on the fact that the default in your brewing software was 38 p/p/g for wheat malt. You’d need the number measured as XX.X p/p/g (or whatever other units you use). For volume, you’d need to measure X.XX gallons (or Y.YY L) — i.e. roughly to the nearest fluid ounce or 10 mL).

The point here is not that you need to start measuring everything more precisely. That’s up to you. The point is to realize what the numbers your brewing software spits out really mean. For example, if your calculated efficiency jumps from 67.53 to 68.38%, should you be happy?

Chris Colby is 98.73% sure that he the editor of BYO.