Brewhouse Efficiency

Malt contains a fixed amount of starch, and mashing converts as much of it as it can into dissolved sugar that leaves with the wort. Brewhouse efficiency is the fraction of that available extract which actually reaches the kettle — recovered over available, a plain ratio of two masses with no fitted constant and no unit trap. Most well-run homebrew systems land between 70 and 80%; commercial breweries with lauter tuns and proper sparge control reach the high eighties.

The number is really two numbers wearing one name, and confusing them is the classic error in this corner of brewing. CONVERSION efficiency asks whether the starch became sugar in the mash tun at all, and on a properly crushed grain bill at a sensible pH it should be well above 95% — if it is not, the mash is the problem. LAUTER efficiency asks how much of that converted sugar you then managed to rinse out of the grain bed, and it is where most losses actually live, because a certain volume of sweet wort is always left absorbed in the spent grain. Brewhouse efficiency is the product of the two. A brewer chasing a low number should measure them separately, because the fixes are entirely different: crush finer and correct the mash pH for one, sparge more patiently and slowly for the other.

What moves the number, roughly in order of leverage: the crush, which should tear the husk open while leaving it intact enough to filter, and which is the single most common cause of a disappointing efficiency; the sparge, where channelling lets water take the path of least resistance and rinse almost nothing; mash pH, which should sit between 5.2 and 5.6 at mash temperature for the amylases to work properly; and mash time, though a mash that has not converted in ninety minutes usually has a crush or a pH problem rather than a patience problem. Batch size matters too, and in an unintuitive direction — the wort left behind in the grain is roughly fixed per kilogram of malt, so it is a larger fraction of a small batch than a large one.

An efficiency above 100% is arithmetically possible and physically not, so treat it as a measurement fault rather than a triumph. The usual causes are a volume read hot and not corrected for thermal contraction, a hydrometer that has never been checked against distilled water, or a potential figure taken from a malt analysis on a different moisture basis than the one you assumed. The last one catches people out regularly: a fine-grind dry-basis extract figure is not the same as a coarse-grind as-is figure, and the gap between them is several percentage points.