Our way of calculating efficiency has changed, and this is noticed on the Recipe Builder page. You can choose your boil size, and the amount of wort at the end by choosing the volume going into the fermenter, or the volume at the end of the boil. Those choices do NOT impact your efficiency calculation, but are there to assist you in ensuring your volumes are correct for your brewing. To understand the efficiency calculation, an example is best. Let’s say your boil starts at 6 gallons. You have 120 points of fermentables (e.g. 5 pounds of 30 ppg at 80% efficiency). You boil down to 5 gallons. In this example, your system may lose 1 gallon to kettle dead space, hop absorption, losses to the way you transfer wort, wort left in the chiller, and so on. In this case, you up with 4 gallons in the fermenter. In the old method: You’d select the fermenter target, and enter 6 gallons as your boil size. Four gallons would be your batch size, since that is the volume going into the fermenter. The software assumed that the difference from the 6 gallons at the beginning reducing to 4 gallons as the batch size was all boil-off. As a result, the OG was calculated as: 1 + ( 120 / 4 ) * 0.001 = 1.030 That is clearly wrong because it indicates that all fermentable sugar was condensed into 4 gallons of wort. The reality is that it was condensed into 5 gallons of wort, and some of that was simply thrown away. The loss of wort does not increase specific gravity of the remaining wort, of course. The loss would have the same SG as the wort going into the fermenter. So in our updated calculation, you would select the batch size of 4 gallons as the target into the fermenter, enter 6 gallons as pre-boil size, and 5 gallons as post-boil size. You can also let the system calculate from your equipment profile’s boil-off rate. Now the OG can be calculated correctly: 1 + ( 120 / 5 ) * 0.001 = 1.024 You will notice that it is a 20% difference. That seems small to some, but we wanted to give the most accurate OG predictions possible for our users, both homebrewers and professionals.