I am reading the brewhouse yield section of "a Handbook of Basic Brewing Calculations" and it states in order to know your brewhouse yield one piece of information needed is your brewhouse efficiency. In the book it seems to me they guess at an efficiency but how does one calculate this number?
There are several efficiency calculations that are good to know from your brewhouse and every operation will be different depending on the process and materials used. However the calculations for everyone are basically the same. Let’s start with your mash yield which is a measurement of how much of the available starch you are converting and extracting from your mashing/lautering process per the amount of material used.
Mash yield = Lbs of extract collected/lbs of malt (or other material) used.
To get lbs of extract you need to accurately measure the volume of wort collected in your brewkettle (remember to multiply this number by 0.96 to account for thermal expansion) and the degrees Plato. You can get the lbs extract/bbl from extract tables (MBAA Practical Handbook for the Specialty Brewer Table 5.2) or using the equation:
[(259 + deg P)deg P]/100
Normally the mash yields will be about 65% for malt, 75% for corn grits and 82% for syrups. This is a useful ratio used to calculate recipe grist weights.
Brewhouse efficiency is simply a ratio of what is recovered vs what was put in: Lbs of extract collected divided by lbs of extract potential from the grist. Although this efficiency ratio can be used at any step in the process, ie lauter to kettle, kettle to whirlpool tank, etc, ultimately brewhouse efficiency uses this ratio of outputs to inputs to measure just how efficiently the brewhouse has used the malt and other materials to produce a given volume of wort at a particular Original Extract (OE). The higher the number, the less waste and loss.
To determine your brewhouse efficiency you will need to know how much extract is in each ingredient in the grist. The malt house will supply a Certificate of Analysis and on the COA are numbers for % extract. The listed extracts will normally include a “Fine Grind dry basis” which is the ultimate available amount of extract in complete extraction and does not include the weight of moisture. The more practical “Coarse Extract as is” (moisture included) will give you a more realistic limit of how much your brewhouse could yield from the malt and is the number to use when making efficiency calculations.
The brewhouse efficiency then will be a ratio between what you could possibly expect to yield and what you actually yield. To determine efficiency first multiply the coarse grind as is extract % by the weight of the grist for each component, ie lbs pale male x X% coarse extract to get lbs extract possible from pale malt, same with crystal malt, wheat malt, etc. Total up the weight from each and this will give you total lbs of extract potential in the grist.
Your final yield from the brewhouse can be defined as the amount of extract actually recovered as cold wort in the fermenter compared to what you started with in the mash tun. To get that number you will accurately measure the volume of cooled wort collected in the FV tank and its gravity in degrees Plato. From the extract tables or extract equation determine the lbs of extract/bbl. Multiply the lbs extract/bbl by the bbls of wort collected to get lbs of extract in the FV. This is your realized lbs of extract from the grist.
Total up the lbs of potential extract from your grist and then divide into the lbs of extract collected in your fermenter and this will give you the brewhouse efficiency. You can use this same ratio at each step in the brewhouse process to determine efficiencies and find sources of losses. Brewhouse efficiencies of 90-93% for single infusion mash tuns are possible with a good mill, grind control and good lautering practices as well as minimal losses through to the FV tank. Automated brewhouses with a lauter tun or mash filter will see brewhouse efficiencies of 96-98%.