Originally Posted by rawlus
Read the beersmith guide. They go into how to determine those figures, most of he software programs have the efficiency built into their software, many grains will also list their potential on packaging, and there is a chart here http://www.beersmith.com/grain-list/
That's great, thanks!!
So, when you create a grain bill, you generally use a variety of different grains, each of which I imagine would have different potential SGs. So, how do you work out the overall potential SG of your wort? Do you just add them together and make an average or something?
Also, it seems strange that in that chart you linked, none of them have a potential SG of 1.050 or higher. So, how is it possible to obtain an OG of 1.050 or higher? I'm obviously missing something basic here....
EDIT: Here is the information required to make those calculations;
"Lets look first at how to calculate the total potential of the grain for a batch of beer:
(potential_pts) = (grain_pts) * (weight lbs) / volume_gals
Each grain has a dry grain potential, which you can find from our grain listing or from the malter’s web site. The grain_pts is calculated from the grain potential by subtracting 1.000 and multiplying by 1000. For example, a grain with a potential of 1.035 becomes simply 35 points. 5 pounds of this grain in a 5 gallon batch would add 35*5/5 = 35 potential points to the beer. If we sum all of the potential points from the various grain additions we can get the overall potential. If we had no losses in the system, the 35 points above would give an ideal starting gravity for our beer of 1.035.
I mentioned that the potential points represents the gravity under ideal conditions. In practice one gets much less than this, usually around 70-80% for brewhouse efficiency overall. Therefore the actual original gravity is determined by the potential points times the gravity:
(batch_pts) = (potential_pts) * (brewhouse efficiency)
So if we consider a recipe with 40 potential points, and a 75% brewhouse efficiency we get 30 batch points or an original gravity of 1.030. This is how original gravity is estimated.
Reversing the calculation we can calculate the efficiency from an ideal recipe potential estimate (potential_pts) and actual measurement (measured_pts).
(efficiency) = (measured_pts) / (potential_pts)
So for example if we had a recipe with potential_pts of 80 and measured the wort into the fermenter 1.050 we get an efficiency of 50/80 = 62.5%. Note that this assumes we hit our target volume. If we don’t, we need to consider the target and actual volume as follows:
(efficiency) = (measured_pts * target_vol) / (potential_pts * actual_vol)
The formulas above give us the overall brewhouse efficiency, but can also be used to calculate the mash efficiency into the boiler. For efficiency into the boiler we simply use the boiler volume and measured boil specific gravity into the boiler as opposed to the fermenter. In BeerSmith you can click on the “brewhouse efficiency” button in any open recipe to perform more detailed mash or overall efficiency calculations."