efficiency calculation - how to account for lactose

[scottsaxman]

I'm trying to figure efficiency by backing into the numbers, but I can't figure out how to (or if?) I need to adjust somehow for lactose addition in the boil.

I'm using BrewMate software, which tells me the OG on a Left Hand Milk Stout Clone should be 1.060 for a 5 gallon batch, assuming 75% efficiency. However, it has you add lactose in a miscellaneous spot with no potential gravity input. I've seen a couple of adjustments on the forums here - from .004 to .009 points - for 1 pound of lactose added in to the boil. Can anyone confirm the appropriate number?

Going into the fermenter, the adjusted gravity reading was 1.063, including the lactose.

 

[corax]

Lactose has the same molecular weight as sucrose, so I'd just use the same potential value as sucrose (1.046 per pound per gallon).

 

[dcp27]

just remove the addition of the lactose (~9pts in this case) to figure out the efficiency. looks like you got about 79%

Lactose has the same molecular weight as sucrose, so I'd just use the same potential value as sucrose (1.046 per pound per gallon).

molecular weight plays no role here

 

[scottsaxman]

https://www.homebrewtalk.com/f68/left-hand-milk-stout-clone-139820/

This is pretty much the recipe we used. It states OG 1.062. Is this including the lactose? If it is including lactose, I understand the 79% efficiency number.

Since I'm a noob, I assumed my efficiency would be less, so I was subtracting the 9 points from the OG (for 1.054) and backing into about 67% efficiency.