1. An efficiency figure is based on taking a gravity reading and a volume reading of sweet liquor, wort or flat fermented beer. Gravity and volume measurements are affected by temperature and usually need to be physically or mathematically manged to get an accurate reading.
2. Efficiency figures based on a single gravity and volume reading are often very inaccurate and cannot be relied on.
3. The new brewer, as mentioned in the Master Guide, should initially concentrate on the taking and recording of readings for their first 5 to 10 brews.
4. Any statement like, "I changed this on my last brew and my efficiency improved by 5%," should be taken lightly." Any statement like, "My first 5 brews averaged x efficiency and my next 5 brews averaged y efficiency," is worth looking into.
5. Efficiency measurements are often wildly inaccurate for a lot of reasons. One major reason is simply through their interpretation. "Efficiency into fermenter," will be vastly lower than, "into boiler efficiency," for example. To keep things congruent, BIABrewers should be encouraged to report their, "post-boil," efficiency. Theoretically, this should be the same as, "into boiler efficiency," but often is not.
6. The term, "brewhouse efficiency," as reported from brewing software is not a good figure to quote to other brewers. It is often derived from incorrect use of software and, in some cases, even the software uses the term badly. It is very hard to find a definitive definition of, "brewhouse," efficiency so when it is used the new or experienced brewer really needs to find out what the source is referring to.
7. BIABrewers, when quoting their efficiency should describe their efficiency figure accurately. For example, "My pre-boil efficiency was..." or "My efficiency into the fermenter was.." New brewers who think they have an efficiency problem should go further still. They should say at what stage they took their reading as well as the gravity of the reading (at room temperature) and the volume of the sweet liquor or wort from which it was taken.
8. Post-boil efficiency is the best figure to work from as gravity of unfermented wort does not change until after pitching.
9. How to take gravity and volume measurements at various stages of the brew needs to be written somewhere but not sure which section to put it in. The importance of temperature on gravity readings and volume should be referred to. For example, if a hot reading is taken, it needs to be covered in plastic wrap and chilled. Hot volume measurements need to be calculated out.
10. Whilst the above discredits the importance of efficiency it is important that major efficiency failures can be identified early by the new brewer. So, this post also needs to give the new brewer a ball-park guide of how to interpretate their readings.
11.There could perhaps be an efficiency failure checklist in future. For now, more experienced brewers should be able to help. Usual failures are, inaccurate or non-calibrated hydrometers, inaccurate thermometers, bag doesn't line the pot, bag of wrong material or no stirring of mash. Never seen crush of grain as a problem. All others have been the causes to date. Whoops, there is another common one - incorrect weighing of grain bill by supplier or the brewer.
12. BIABrewer fears that this subject will take a long time to get right so, for now, when you quote an efficiency figure, please follow the guidelines above as best as you can.