Grist Bill Builder

Predicting Original Gravity

This is a calculator for predicting Original Gravity (OG) in a beer recipe. This is often done by using Brewhouse Efficiency, which can also be defined as “to the Fermenter” efficiency. A gravity measurement and volume of wort that made it (or will make it) to the Fermenter are needed for this calculation. 100% Brewhouse Efficiency means that all of the available extract from the grist has made it to the Fermenter. For home brewers, this does not happen. The range of your Brewhouse Efficiency will highly depend upon the equipment you are using and your familiarity with it. As an example, for traditional mash/sparge brewing, 75% is a number many use. For Brew-In-A-Bag (BIAB) brewing, 65% may be a good starting point.

Grist Input Numbers

Input numbers from lab analysis are available from the Maltster and may vary over time for the same malt. Also, a range or maximum number is often given, so you’ll have to pick a number within the range or between zero and the maximum.

The professional bodies that standardize these analyses are The Institute of Brewing (IoB) for the UK, The European Brewing Convention (EBC) for Continental Europe, and The American Society of Brewing Chemists (ASBC) in the US.

Here are some notes regarding the input numbers:

  • Points Per Pound Per Gallon (PPG) represents the gravity points contributed by one Pound of malt in one US Gallon of wort. This number is not given by a maltster, but is sometimes available in tables. Please consider the origin of this number before using it.
  • IoB – Hot Water Analysis (HWA) is used in the UK as a standard to measure available extract. The units used are Litre Degrees per Kilogram.
    • If As Is, no adjustment to the number is needed
    • If Dry, then Moisture Content (MC) will be need for a correction.
  • Dry Basis Coarse Grind (DBCG) is indicative of the degree of starch modification and closer to the grind the brewhouse would use, so the maximum extract would be similar. Since this is Dry, then the Moisture Content (MC) will be needed for a correction. If there is only one number (roughly between 60 and 80) which is not specified and MC is also listed, then it’s relatively safe to assume it’s DBCG.
  • Dry Basis Fine Grind (DBFG) is indicative of the maximum amount of solubility, for which a grind so fine would not be practical in a brewhouse. DBFG needs to be corrected for both Moisture Content (MC) and the Difference (FG/CG). Difference (FG/CG) is the difference in percent, not ratio, between the DBFG and DBCG.
  • As Is Coarse Grind (AICG) is like the dry, but no correction is required. If you don’t know what number to use and have no other information, select this and use 77%.
  • As Is Fine Grind (AIFG) is like the dry, and only the Difference (FC/CG) is needed for correction.

Note: This calculator is calibrated to 20°C for water volume to weight conversions.

Grist Bill Builder
Grist Bill Builder
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