Lactose additions and calculating gravity and ABV

[hoppyscotty]

Brewed a NEIPIA last weekend. The recipe called for 200g of lactose to be added into the whirlpool stage then another 200g added in the fermenter at the same time as the dry hop addition. The recipe OG was 1.059. We achieved about 1.047 before adding the lactose and once the lactose was added we achieved the 1.057 OG.

The recipe is not specific in terms of the OG including the lactose or excluding it. If I run the headline recipe numbers through an ABV calculator I can get the ABV to match up with the recipe so the OG and FG of the recipe ties up with ABV. So on the fact of it, it seems the recipe OG and FG and resulting ABV include the lactose additions and that lactose is fermentable?

Is my understanding that lactose is not fermentable incorrect? Otherwise I have no idea how to calculate ABV. If I back out the impact of the lactose additions my ABV falls way short of the recipe ABV - about 3.8% or so.

Thanks.

 

[Hazelwood Brewery]

Lactose is not fermentable. It will add sweetness and body to the beer but will not contribute to the ABV.

If your gravity was 1047 before adding lactose (and assuming a typical FG of around 1010) you would get an ABV around 4.8%.

Adding the lactose is giving you a higher OG and will also result in a higher FG but the difference between the two should be the same - around 35-40 points depending on mash temperature and yeast selection.

A 10-point difference from 200g is quite a lot, is this a 10-litre batch?

 

[hoppyscotty]

Thanks, what I was thinking. It was a 18 litre batch - was supposed to be 19 litres but extended boil to bump up gravity a bit and sacrificed some. I'm sure I Messed up in the mash and undershot the extraction from the mash altos...maybe by as much as 10 points, but struggling to work out by how much and how to work out what final ABV will be with 400g of lactose in there. Ultimately doesn't matter so long as it tastes OK, but always like to know if I've hit my numbers and the intent of the recipe.

 

[Hazelwood Brewery]

Did you take the OG, including 200g of lactose, when you put the wort into your fermenter? Is this the 1057 you noted?

What were the OG, FG, and ABV published for this recipe?

 

[hoppyscotty]

According to Brewfather the pre-boil gravity was 1.048 (no corresponding figure for this included in the recipe) and before adding the 200g of lactose in the whirlpool we were short...I think we were around 1.035. We then added the lactose and that brought us upto about 1.042.

We boiled for an hour as per recipe, and after that the gravity was short of the recipe 1.057 so we extended for another 20 mins or so boiling off an additional litre to bring gravity in and by the time we chilled and pitched into the fermenter we were at 1.056 so only point off...but including the lactose.

Recipe called for dry hop and another 200g of lactose 'towards the end of fermentation'. It was Kveik so was fermenting like a rocket so I dry hopped and added the lactose as the initial crazy phase of fermentation was starting to subside, as I didn't want to go to bed and miss it, and a gravity reading at this point was 1.028...before adding the 200g of lactose. I didn't take another gravity reading after adding the lactose. Fermentation then quickly slowed down but has been creeping down over the last couple of days but think I'm nearing the end. I have an iSpindel so tracking fermentation but I know the gravity numbers are out as I cocked up the calibration so just tracking the trend and difference in gravity numbers.

Strangely enough the iSpindle registered an increase in gravity when I added the lactose, but after 24hrs this 'bump' had reduced and the trend caught upto where it would have been if I'd have not added the lactose. I can't trust the iSpindel until I re-calbrate it.

I think I'll hit the recipe FG of 1.017 but including the lactose....but if I subtract an assumption for the lactose addition I'm a good couple of % down - from 5.5 to about 3.8/4%.

I'm convinced I have been about 10 points down on gravity throughout the process so expect a drop in ABV.No problem really just struggling to understand how to account for lactose additions to back track them out of the gravity calculations.

 

[Hazelwood Brewery]

If you want to know how many points have been contributed by the lactose we can start with your OG of 1056 (including lactose) and volume of 18 litres…

Lactose contributes 35 points-per-pound-per-gallon(US). 200g is 0.441 lbs so would contribute 35x0.441=15.44 points per gallon(US). You had 18 litres which is 4.76 gallons. The 200g of lactose therefore added 15.44/4.76=3.24 points.

You then added another 200g so will have added another 3.24 points. Approx 7.5 points in total.

The 3.24 points added in fermentation would not have been included in the OG. Adding this back in to the OG will give you 1056+3.24=1059(ish), FG of 1017, points fermented = 42 and ABV of 5.5%.

…probably! Anyone check my maths?

 

[hoppyscotty]

Thanks, I'll check your maths later and see if I can backtrack and back out the lactose impact from both the first and second addition.

 

[Hazelwood Brewery]

Thanks, I'll check your maths later and see if I can backtrack and back out the lactose impact from both the first and second addition.

I think you’re fine. If it’s easier, forget about adding the points from the fermenter addition to the OG, just remove 3.24 points from the FG

1056 - 1014 = 42
42 x 0.13125 = 5.51%

 

[moto748]

I had a go at a milk stout a while back. After reading up, and still struggling with similar to the above, I thought... d'you know what, I don't really like milk stout that much anyway!

 

[Hazelwood Brewery]

I had a go at a milk stout a while back. After reading up, and still struggling with similar to the above, I thought... d'you know what, I don't really like milk stout that much anyway!

It’s only odd because of the lactose addition during fermentation. I don’t remember ever having seen that before.

 

[hoppyscotty]

Yeah sounded odd but that’s the recipe. Not sure how adding it to fermentation modifies the flavour.
I’m not actually keen on lactose in beer either. If I want a malty, milky beverage I’d have a mug of Horlicks. But a mate chose the recipe.