Recipe Calculation Clarification

[beerdrinker]

Another Sunday well spent out with the brew kettle, however my efficiency seems quite off for the recipe:

Amarillo Pale Ale
2.5 Gallon Batch

Grain Bill:
4.5 lb - 2 Row Malt
0.5 lb - Caramunich II Malt

Hops:
7 g Perle(60)
14 g Amarillo(10)

Yeast:
BRY-97 American West Coast Ale

I was expecting the OG to be around 1.054 SG, however it turned out to be only 1.040 which seems quite low, I rarely have efficiency issues. The only real change here to my style is that it was a 2.5 gallon batch versus 5 gallons usually. One thing that jumps out is that my kettle has about a gallon below the valve line and if that is added in it would be 3.5 gallons and 1.040 SG would have been 87% efficiency.

Needing to account for the trub/leftovers in the kettle would make sense as I thought I usually got about 75% efficiency at 5 gallons but if I adjust up to 6 gallons would have me at 85-90% efficiency on recent batches which would match the efficiency of the 2.5 gallon batch.

Would you guys use the final volume as what goes to the fermentor, or what is left in the kettle?

Either way the beer looks and smells great, I've just got more of a session beer than an American Pale Ale.

Cheers!

[mobrewer]

It may depend on your calculation method or software profile. I have my BrewToad account set for 1 gallon of mash tun loss.

[BDawg]

This is one of the reasons that efficiency is really only useful on your own system.
You need to calculate it the same way every time, then work on your processes so that what you enter is what you actually end up with.

In some systems, 70% is kicking ass (when there are lots of losses, etc).
In others 80% would be considered a crappy day.

Include your losses so you know how to calibrate volume. Measure what you end up with.
Next batch, use the same losses and efficiency, but tweak the base malt to hit what you desire.
Brew that, and measure to see exactly how you did, and re-tweak.
Eventually, you'll figure you exactly what you need to plug in and you will be able to nail it every time.