One thing that I would like to add to the discussion is that software generated efficiency percentages are only accurate if the actual hot water extract (HWE) or dry basis, fine grind (DBFG) values of the malted cereal grains used in a mash match the values used to perform the calculation. The HWE/DBFG values for different malted cereal grains change from year to year and malting to malting because the maltster is at the mercy of mother nature, which is one of the reasons why I switched to using a simple moving average points per pound per gallon-based system years ago. I have seen more than one amateur brewer beat him-/herself up over decreases in extraction efficiency when his/her efficiency did not change--the actual HWE/DBFG values of the malted cereal grains used in the mash changed!
With that said, I posted my system a while back in a thread that turned ugly. I do not wish to have this thread go in that direction. If my system works for you, I am happy to see others adopt it. However, I know that most people will continue to use the system that works for them.
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Here's a strategy for incorporating points per pound per gallon into one's brew house:
First, one needs to calculate the points per pound per gallon extraction rates for one’s brew house.
points_per_pound_per_gallon = (batch_original_gravity - 1.0) x 1,000 x batch_volume_in_gallons / batch_grist_mass_in_pounds
In practice, the (batch_original_gravity - 1.0) x 1,000 portion of the equation can be simplified by taking the original gravity reading lopping off the "1" and converting the number to the right of the decimal point to a whole number (e.g., 1.056 becomes 56), as that's all this part of the equation accomplishes.
Using a 5.5-gallon batch of 1.056 wort that was made with 11 pounds of grist to put the equation into practice yields:
batch_original_gravity = 1.056
batch_volume_in_gallons = 5.5
batch_grist_mass_in_pounds = 11
points_per_pound_per_gallon = (1.056 - 1.0) x 1,000 x 5.5 / 11 = 28
Now, if we perform this calculation for several batches, sum the points per pound per gallon values, and divide by the number of batches that were summed, we will arrive at our average brew house extraction rate in points per pound per gallon.
Example
Batch #1 = 26.5 points per pound per gallon
Batch #2 = 27 points per pound per gallon
Batch #3 = 30.5 points per pound per gallon
Batch #4 = 28 points per pound per gallon
Batch #5 = 29 points per pound per gallon
average_points_per_pound_per_gallon = (26.5 + 27 + 30.5 + 28 + 29) / 5 = 28.2
With experience, the variance in the points per pound per gallon values from batch to batch will narrow, and one will have a solid metric with which to use in recipe formulation.
Now that we have found our average brew house extraction rate, let's put it into practice using a hypothetical 11-gallon recipe that we would like to adjust for our 5.5 gallon brew house.
Simple Pale Ale
batch_original_gravity = 1.064
batch_volume_in_gallons = 11
batch_mass_in_pounds = 23
Grist Composition
British Pale Malt: 20.75 pounds
60L Crystal Malt: 2.25 pounds
Calculating the recipe points per pound per gallon extraction rate yields :
recipe_points_per_pound_per_gallon = (1.064 - 1.0) x 1,000 x 11 / 23 = 30.6
If we compare the recipe’s extraction rate to ours, we will clearly see that we cannot just cut the recipe in half; therefore, we need to scale the grist to fit our brew house extraction rate. We can handle scaling two different ways. The easiest and most logical way is to calculate the amount of grist that that we will need to hit the recipe’s O.G. in our brew house and divide this mass into malt percentages that are proportional to those found in the original recipe.
Calculating how many pounds of grist that we need to hit 1.064 yields:
batch_grist_mass_in_pounds = (batch_original_gravity - 1.0) x 1,000 x batch_volume_in_gallons / average_points_per_pound_per_gallon
batch_grist_mass_in_pounds = (1.064 - 1.0) x 1,000 x 5.5 / 28.2 ~= 12.5lbs
With that calculation complete, we need to calculate grist percentages from the original recipe.
recipe_total_grist_mass = 23lbs
recipe_british_pale_ale_percentage = 20.75 / 23 x 100 ~= 90%
recipe_60L_crystal_percentage = 2.25 / 23 x 100 ~= 10%
With these numbers, we can now formulate our grist.
Our Simple Pale Ale
batch_original_gravity = 1.064
batch_volume_in_gallons = 5.5
batch_grist_mass_in_pounds = 12.5
British Pale Malt: 12.5 x 0.9 = 11.25lbs (11.25 is 90% of 12.5)
60L Crystal Malt: 12.5 x 0.1 = 1.25lbs (1.25 is 10% of 12.5)
The second way to adjust a recipe based on one’s brew house extraction rate is to calculate a grist scaling factor that takes into account the differences in brew house extraction rates and a batch volume divisor that takes into account the difference in batch volumes.
grist_scaling_factor = recipe_extraction_rate / our_average_extraction_rate
grist_scaling_factor = 30.6 / 28.2 ~= 1.085
batch_volume_divisor = recipe_batch_volume / our_batch_volume
batch_volume_divisor = 11 / 5.5 = 2
batch_grist_mass_in_pounds = recipe_grist_mass_in_pounds x grist_scaling_factor / batch_volume_divisor
Our Simple Pale Ale
batch_original_gravity = 1.064
batch_volume_in_gallons = 5.5
batch_grist_mass_in_pounds = 23 x 1.085 / 2 ~= 12.5
British Pale Malt: 20.75 x 1.085 x 0.5 ~= 11.25
60L Crystal Malt: 2.25 x 1.085 x 0.5 ~= 1.25
(note: the symbol “~=” denotes approximately equal to)
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