How to read and improve mash efficiency
What gravity points and PPG mean, why the same batch can show two efficiency numbers, and practical ways to lift your yield.
Points, PPG and where efficiency comes from
Efficiency compares the sugar you collected to the sugar the grain could give. The grain side is simple: each pound of base malt can contribute about 37 gravity points in one gallon, so ten pounds offer 370 potential points. The wort side is your reading: subtract one from the gravity, multiply by 1000, then by gallons, so 1.050 in five gallons is 250 actual points. Dividing actual by potential and multiplying by 100 gives the percentage this tool reports. Everything hinges on accurate gravity, volume and PPG figures.
Mash versus brewhouse efficiency
The same brew can honestly show two different efficiency numbers depending on where you measure. Measured from the pre-boil wort, you get mash or lauter efficiency, which reflects how well you converted and rinsed the grain. Measured from the cooled wort going into the fermenter, you get brewhouse efficiency, which is always lower because it also absorbs boil-off, kettle deadspace and trub loss. Decide which one you care about and always measure at the same point so your numbers are comparable brew to brew.
Common reasons the number is low
A low figure usually traces to conversion or lautering rather than the grain itself. A coarse crush leaves starch locked inside husks, so tightening the mill gap often adds several points. Channeling during the sparge lets water rush past the grain bed instead of rinsing it evenly, and a mash that is too thick or too cool converts less starch to sugar. Skipping a mash-out or vorlauf, or sparging too fast, all leave sugar behind that shows up as a smaller actual points total.
Using the figure to plan a recipe
Once you know your system's typical efficiency, you can size a grain bill to hit a target gravity instead of guessing. Rearrange the math: needed potential points equal target actual points divided by your efficiency as a decimal, and grain weight equals potential points divided by PPG. Brewers who track this over several batches get a stable number they can trust, which makes original gravity predictable and keeps alcohol and bitterness balanced from one brew to the next.