What efficiency measures, and why brewers argue about it
Efficiency is a fraction with a measured numerator and a theoretical denominator. The denominator is the most sugar the grain could possibly give: every malt has a laboratory extract figure, and multiplying weight by that figure and adding up the bill gives you the ceiling. The numerator is what you actually got, calculated from a gravity reading and a volume. Divide, and you have a number that summarises how well your mill, mash and lauter worked on that particular day.
Brewers work in gravity points for this, because points are conserved and gravity is not. A gravity of 1.048 in six gallons is 48 × 6 = 288 points. Boil it down to five gallons and the gravity rises to 1.0576, but the points are still 288 — you removed water, not sugar. That property is what makes points the right currency: they let you compare a measurement taken before the boil with one taken afterwards.
The arguing starts with which measurement point to use, and it is a real disagreement rather than a pedantic one. Mash efficiency uses the pre-boil reading. It measures the mash and the lauter, and nothing else. Brewhouse efficiency uses the wort that actually reached the fermenter, so it also charges you for every gallon of sweet wort abandoned under the hop bed and every drop lost in the transfer. Because boiling conserves extract while later steps only lose it, brewhouse efficiency comes out at or below mash efficiency on any honest set of measurements.
Recipe software normally scales grain bills using brewhouse efficiency, because that is the figure that predicts your original gravity. Mash efficiency is the diagnostic figure: it isolates the part of the process you can fix with a mill adjustment or a longer rest.
PPG, and where the number on the malt bag comes from
PPG stands for points per pound per gallon: the gravity points one pound of that malt yields when dissolved in one gallon of water, at perfect extraction. Pure sucrose, which dissolves completely, gives about 46 PPG, and that is the practical ceiling for any fermentable. Malt is a grain kernel, so part of its mass is husk, protein and moisture that never dissolves; well-modified pale malt reaches about 37, which is roughly 80% of sucrose's figure.
Maltsters do not publish PPG. They publish fine grind dry basis extract, a percentage from a standardised laboratory mash on flour-milled malt with the moisture subtracted out — typically 79 to 82% for base malt. Convert with PPG ≈ 46 × FGDB: a malt spec'd at 81% FGDB gives 46 × 0.81 = 37.3 PPG. If you want the as-is figure rather than dry basis, multiply again by (100 − moisture%)/100, which knocks off another 4% or so.
Two consequences matter on brew day. First, the laboratory number comes from a flour-fine grind that no homebrew mill produces, so 100% efficiency is unreachable by construction — the standard is deliberately an upper bound. Second, the figures move between harvests and between maltsters. If your efficiency drops three points when you switch suppliers, check their spec sheet before you rebuild your mill.
Sugars are the exception that flatters your numbers. Table sugar dissolves completely at 46 PPG regardless of what your mash does, so a recipe with a pound of candi sugar in it will always report a higher apparent efficiency than the same recipe without. When you compare efficiency across brews, compare the all-malt ones.
Worked example: an 11.5 lb grain bill
You mash 10 lb of 2-row pale (37 PPG), 1 lb of crystal 60 (34 PPG) and 0.5 lb of chocolate malt (28 PPG). You collect 7.0 US gallons at 1.044, boil for an hour, and transfer 5.5 gallons at 1.054 into the fermenter.
- Maximum points. (10 × 37) + (1 × 34) + (0.5 × 28) = 370 + 34 + 14 = 418 points.
- Weighted potential. 418 ÷ 11.5 lb = 36.3 PPG for the bill as a whole.
- Points collected pre-boil. (1.044 − 1.000) × 1000 × 7.0 = 44 × 7 = 308 points.
- Mash efficiency. 308 ÷ 418 = 73.7%.
- Points into the fermenter. 54 × 5.5 = 297 points.
- Brewhouse efficiency. 297 ÷ 418 = 71.1%.
- PPG achieved. 297 ÷ 11.5 = 25.8 PPG against the bill's 36.3 ceiling.
The 11 points of difference between the two efficiencies is not a mash problem at all — it is the 308 − 297 = 11 points of sweet wort you left in the kettle, about 0.2 gallons at that gravity. If you want brewhouse efficiency up, you can improve the mash or you can stop abandoning wort under the hops, and this arithmetic tells you which is worth more.
What number should you be hitting?
Typical homebrew brewhouse efficiency runs 65 to 75% on a cooler or kettle system with a moderate crush. Well-tuned systems with a tight mill gap, a mash-out and a proper fly sparge reach 80 to 85%. Brew-in-a-bag without sparging usually lands 60 to 70%, because you leave all the sugar held in the wet grain behind in one go. Commercial breweries with mash filters and fine milling routinely exceed 90%, using equipment that no homebrewer has.
The absolute number matters far less than its consistency. Efficiency's job in your process is to let you predict a gravity before you brew, and a system that reliably gives 68% is more useful than one that averages 76% and swings ten points either way. If yours is erratic, the first suspects are the volume measurements — a dipstick read at eye level in a wide kettle is easily out by half a gallon, which is worth six points of efficiency — and hot-versus-cold volume readings, since wort shrinks about 4% on cooling.
If your efficiency is consistently low, work through the causes in order of size. Crush is nearly always first: kernels that come through whole cannot give up their starch, and closing a mill from 0.045 in to 0.035 in commonly moves efficiency five points or more. Mash temperature is second — a mash that landed at 145 °F instead of 152 °F converts more slowly and may not finish in an hour, which the strike water temperature calculator prevents. Sparge technique is third: a fast, hot runoff channels through the bed and rinses badly, and skipping the sparge entirely costs the most of all. pH is fourth; a mash outside roughly 5.2 to 5.6 converts less completely.
Watch for the phantom efficiency gain, too. If your figure jumps after you change the recipe rather than the process, check whether you added sugar, which extracts at 100% by definition and drags the average up without any improvement in your brewing.
Extract potential of common fermentables
| Fermentable | PPG | Approx. FGDB | Notes |
|---|---|---|---|
| 2-row pale malt | 37 | 80% | The reference base malt |
| Maris Otter / UK pale | 38 | 83% | Slightly higher extract than US 2-row |
| Pilsner malt | 37 | 80% | Needs a longer rest or a step mash in some lots |
| Munich malt | 37 | 80% | Enough diastatic power to convert itself |
| Vienna malt | 36 | 78% | |
| Wheat malt | 39 | 85% | No husk; blend with barley to keep the bed loose |
| Flaked oats | 33 | 72% | Pre-gelatinised, contributes body more than extract |
| Flaked maize | 39 | 85% | |
| Crystal / caramel 40L | 34 | 74% | Already converted; needs no enzymes |
| Crystal / caramel 120L | 33 | 72% | |
| Chocolate malt | 28 | 61% | Much of the mass is roasted, not extractable |
| Roasted barley | 25 | 54% | Unmalted and heavily roasted |
| Dry malt extract | 44 | — | Dissolves fully; no mash efficiency applies |
| Liquid malt extract | 36 | — | Roughly 20% water by weight |
| Table sugar (sucrose) | 46 | — | The practical ceiling for any fermentable |
| Corn sugar (dextrose) | 42 | — | Sold as the monohydrate, which carries water |
The FGDB column is the laboratory figure the PPG is derived from, using PPG ≈ 46 × FGDB. Extracts and sugars dissolve completely, so including them in a grain bill raises apparent efficiency without your process having improved.
Measure volume cold, or correct for shrinkage
Wort contracts about 4% between boiling and room temperature. A kettle marked at 5.5 gallons of boiling wort holds about 5.28 gallons once cooled, and if you calculate efficiency using the hot figure against a cold gravity reading you will overstate it by roughly four percent of itself — three points on a 70% system. Pick one convention and hold to it: either mark your dipstick with cold water and correct hot readings down, or measure everything hot and be consistent. Mismatched hot and cold volumes are the most common reason a brewer's efficiency wanders without explanation.
What actually moves the number
- Mill gap. The biggest single lever. Aim for kernels crushed open with the husks left largely intact; whole kernels passing through are wasted money.
- Sparging at all. A no-sparge or full-volume BIAB mash leaves the sugar held in the wet grain behind, typically costing 8 to 12 points of efficiency against a batch sparge.
- Mash temperature and time. A mash that missed low, or a sixty-minute rest cut to thirty, may not have finished converting. Iodine still turning black means starch is left.
- Runoff speed. A fast runoff channels through the grain bed instead of rinsing it evenly. Forty-five minutes of fly sparging is not fussiness.
- Kettle and transfer losses. These affect brewhouse efficiency only, and are fixed with a hop spider, a whirlpool and a pickup tube, not with a better mash.
- Volume accounting. Half a gallon of error on a five-gallon batch is ten percent of the answer. Work your volumes out ahead of time with the mash and sparge water volume calculator.
Using efficiency to design recipes
Once your efficiency is stable, run the calculation backwards to size a grain bill. If you want 5.5 gallons at 1.055, you need 55 × 5.5 = 302.5 points into the fermenter. At 72% brewhouse efficiency you need 302.5 ÷ 0.72 = 420 points of maximum extract, and at a weighted 36 PPG that is 11.7 lb of grain. Every published recipe carries an implied efficiency, usually stated in the header; if yours differs, scale the whole grain bill by the ratio of the two rather than adding a pound and hoping.
Efficiency also interacts with bitterness in a way that catches people out. A batch that overshoots its gravity has a denser boil than planned, so hop utilization drops and the beer comes out under-bittered as well as stronger — check the effect with the Tinseth IBU calculator before you decide the recipe was wrong. It interacts with yeast too: a wort that lands five points high needs a proportionally larger pitch, which the yeast pitching rate calculator will size for you.
Finally, keep efficiency in proportion. Chasing the last five points is worth a few dollars of malt per batch, and the effort is usually better spent on fermentation temperature control, which changes how the beer tastes rather than how much of it you get. Efficiency's real value is predictability: knowing what gravity you will hit means the beer you designed is the beer you brew, and you can confirm that afterwards with the ABV and attenuation calculator.