flbrewer, if it helps, you can bypass efficiency percentages and work directly in points per pound per gallon. I prefer to use extraction rates in points per pound per gallon because it is a directly applicable value. Extraction efficiency is an indirect value that requires an additional weighted computation to be performed.
total_gravity_points = 6.25 * 60 (1.060 in gravity points) = 375
points_per_pound_per_gallon = total_gravity_points / grist_weight
points_per_pound_per_gallon = 375 / 16 = 23.44
What this value means in layman's terms is that the original recipe was formulated to achieve an extraction rate of 23.44 gravity points per pound of grain, that is, the extract from one pound grain dissolved in a one gallon solution has a specific gravity of 1.02344 That's a value that can be easily applied in one brew house. Working the other way yields:
original_gravity = points_per_pound_per_gallon * grist_weight / batch_volume / 1000 + 1.0
original_gravity = 23.44 * 16 / 6.25 / 1000 + 1.0 = 1.060
The way to determine one's brew house extraction rate in points per pound per gallon is to simply track the original gravity and total final boil volume minus the break and hops for each batch. For each batch in the sample, calculate a batch extraction rate using the following formula:
batch_extraction_rate = original_gravity_in_points * batch_total_volume / grist_weight
I calculate this value when I take my original gravity reading. After a few batches have been brewed, it's time to calculate an average batch extraction by summing the batch extraction rates and dividing by the number of batch extraction rates.
Batch Extraction Rates
Batch #1 - 28 points per pound per gallon
Batch #2 - 27 points per pound per gallon
Batch #3 - 29 points per pound per gallon
Batch #4 - 30 points per pound per gallon
Batch #5 - 29 points per pound per gallon
average_batch_extraction_rate = 28 + 27 + 29 + 30 + 29 / 5 = 28.6
Now, we can convert the recipe to our brew house by calculating a grist scaling factor. Our extraction rate is higher than the original extraction rate; therefore, this value will be less than one.
grist_scaling_factor = 23.44 / 28.6 = 0.82
All we need to do from this point forward is to multiply every quantity in the grist by 0.88 to scale the grist to our brew house. We do not need to adjust the hop bill because the bitterness unit to gravity unit ratio will remain the same.
While what I just wrote seems like a lot of work, what you will find over time is that these calculations become automatic, and you will no longer have to compute an average batch extraction rate because your extraction rates will converge within a close enough range that you can ball park it without actually performing the calculation. When that happens, you will be able to look at a recipe for 6.25 gallons 1.060 wort, and think I need to use 60 / 28.6 = 2.1 pounds of malt per gallon to hit that gravity. At that point, you will prefer to look at recipes as percentages, which is the way that professional brewers state recipes. For example, we are making a bigger version of SNPA, which is often quoted as having a grist that is 95% 2-Row and 5% C60.
total_grist_weight = 2.1 * 6.25 = 13.125 pounds
pounds_of_2Row = 13.125 * 0.95 = ~12.5
pounds_of_C60 = 13.125 * 0.05 = ~0.65
As you have more than likely already ascertained, the values add up to more than 13.125 pounds. I rounded to make measuring a little easier.
With the above said, why should anyone learn how to perform these calculations when brewing software will shield one from having to learn this information? Well, learning how to brew using brewing software is not the same thing as learning how to brew. Learning how to brew means mastering all of the brewing fundamentals that are encapsulated in brewing software.
I hand calculate my recipes. I use points but my formula is different. I do batch points the same. Final volume x gravity points. But that's where it ends. I determine the percentages of each grain in the bill. Let's say 80% two row. We'll just use your example. 80% x 375 = 300. Now I need to know the potential extract of the malt. With two row, it's 38. And I need to know the brewhouse efficiency. In my case, it's 75%. So, I divide my points by potential extract x brewhouse efficiency.
300/(38x.75) = 10.53
So, This recipes calls for 10.5 lbs of two row. I'll do the same process for the rest of the malts.
This method is from Daniels "Designing Great Beers"
It's simple and works for me. It's pretty automatic for me at this point.
I guess we'll both be drinking with the zombies