50% attenuation - Lactose the culprit?

Hi all. I have a Milk Chocolate Stout that's been in Primary for 10 days. It's OG was 1.082, and it has been at 1.034 for about 4 days now. This was an Extract recipe w/ partial mash of grains at about 150*F for 1 hour. Included was 1lb of Lactose, which I realize is largely non-fermentable sugar. Is this finished at 1.034, or should I worry about bottle bombs later? I can always toss some champagne yeast in there or something, but I have no problem twiddling my thumbs and waiting if that's the proper thing to do. Thanks for any input.

P.S. It smells great, looks like its becoming a little more translucent since the last hydro reading, and tastes like a flat, somewhat sweet, chocolaty stout.

I think that when I added lactose (on beersmith anyway) it raises the gravity by about 7 points in 5 gallons. So your FG is probably more like 1.027 giving you an attenuation of about 67%, which isn't bad. I'm would leave it longer definitely, because since you mashed so low I would expect your FG to get a little lower than that.

devilishprune said:

I think that when I added lactose (on beersmith anyway) it raises the gravity by about 7 points in 5 gallons. So your FG is probably more like 1.027 giving you an attenuation of about 67%, which isn't bad. I'm would leave it longer definitely, because since you mashed so low I would expect your FG to get a little lower than that.

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I think that lactose, a sugar, would factor into the actual OG and FG readings, so 1.034 should be accurate.

Lactose isn't 100% fermentable, so it could lead to a higher FG, but 1.034 sounds kinda high - even for a big beer like this.

It could just a coincidence that you have a stuck ferment while using lactose.

Yeah I forgot to ask when it was added. When I made a milk stout I forgot it until bottling, so I didn't have it in my OG. Good call though.

I dont have any problems with attenuation when I use lactose. What temp are you fermenting at? Maybe raise it up a bit to get it going again?

The lactose was added about 10 mins from the end of the boil, 1 pound. Fermentation was very active, it clogged my airlock and I had to rig a blow off tube. It is it my closet hovering around 68-72* F.

What was you yeast pitch / strain like? I'm guessing this is having more impact on you FG than the lactose.

Lactose is 100% NOT fermentable. All you add will be left after fermentation and increase your FG.
1lb in 5 gal adds about 10 points to both OG and FG, assuming you have a 5gal batch.
Crystal malt is also very un-fermentable. Usually only 5% gets attenuated, so depending if you used crystal and how much, you will also end with a higher FG.
Can you post your recipe?

Sure, here's exactly what I did:

Steeped for 1 hour: (temp fluctuated from 150-158, I had a crappy setup)
1# Chocolate Malt
1/2# Crystal 60L
1/2# Pale 2-row
1/4# Carapils
1/4# Black Patent
1/4# Roasted Barley

Extracts:
7# Light LME
1.25# Light DME

Hops: Total 3oz blend of Cascade, Centennial, Amarillo

Adjunct:
1# Lactose
5 oz. Cocoa Powder
(Both were added with 10 mins remaining in boil)

Yeast
WLP002 English Ale - 3Liter starter from stir plate.


I read that WLP002 is highly flocculant, so I agitated the bucket a couple days into fermentation to keep it in suspension. My OG was 1.082, right on the money with BeerSmith's estimate. They estimated my FG at 1.026, but Yooper told me BeerSmith is useless at determining the FG. Still, 50% attenuation seems shady.

From your recipe, into my brewing tool, assuming average mash temp of 155F:

Mashing temperature (F) 155.000
Expected Efficiency% 75.000 (made it 75% to match your OG)
Expected OG 1.082
Expected non-fermentables 1.018
Expected Attenuation% 0.750 (take into account mash temp and use of extract)
Expected FG 1.034
ABV% 6.230

I would say you have reach your FG. Basically, your yeast attenuated 75% of what can be attenuated. The rest is not processed by the yeast.
Although it seems scary a FG of 1.034, let it age for a month or two and you may find it not too sweet as lactose may not add much stweetness but just body to your stout.

I agree with nilo, most of your grains deliver high levels of non-fermentables, plus lactose, plus extract. It's done.

Thank you guys for all the input! This is making a lot more sense to me. I will rack to a secondary with my vanilla bean and as planned, and age it there for at least a month before bottling.

Nilo, that brewing software seems much more efficient than BeerSmith at calculating FG estimates. What do you use? I think I would pay for that before I'd pay $21.95 to register BeerSmith.

I use my own excel tool, where I can assign the level of fermentables for each ingredient.
I also make the yeast attenuation as a function of the mashing temperature.

Damn it. You're just amazing.