Stout ABV too low. Any ideas?

[WarEagleBrewer]

I know it could be any number of things, but I would appreciate any opinion. Here's what we have:

Sweet Chocolate Oatmeal Stout

5lb Marris Otter
1lb Cara-Pils
1lb Oatmeal
13oz Caramel 60
12oz Chocolate Malt
11oz Pale Ale Malt
4oz Roasted Barley
1lb lactose @ 15 mins
1.5oz Kent Goldings
S-04 Dry English Ale yeast

I run all this thru BeerSmith. Single Infusion, Full Body Mash.
I mashed at 156 degrees for 90 mins, mash out for 10 mins, batch sparge till i got 7 gallons. Preboil gravity was 1.037. Added hops at boil, added lactose at 15 mins, boiled off 1.5 gallons. Post boil was 5.5 gals. OG was 1.053. Beersmith says my efficiency sucked....only 67.5%

So i let this sit for three weeks at 68 degrees in a swamp cooler. Airlock stopped bubbling vigorously after 2 days, totally after 3. i didn't take any gravity readings until last night (3 weeks) when i wanted to bottle...and found out the dissapointing results. FG was only down to 1.028. Sample didn't taste very much like beer....but was very malty. I may have wasted a batch, but I pitched another pack of S-04 right into the bottling bucket, gently stirred and popped on a lid and airlock to see what happens in about a week.

Does anybody have any ideas why this didn't get below 1.028? I'm thinking I may have mashed at too high a temp or had a stuck ferm. I always rehydrate my yeast before pitching and haven't had any problems with S-04 before. I'm just interested in theories....thanks!

 

[stpug]

Too high mash temp
Lactose (unfermentable) sugar
S-04 (high flocculating) yeast

S04 has a tendency to drop out before YOU are ready, and it's a notoriously fast fermenter. It can be encouraged to continue by rousing and warm temperatures, which might still work but is much more successful on days 3-7.

There's probably enough sugar that if you pitched a high attenuating belgian yeast you could get that FG lower - maybe 1.020. I don't think any belgian characteristics would come through but even if they did it might work with what you've already got going on.

 

[peterj]

Too high mash temp
Lactose (unfermentable) sugar
S-04 (high flocculating) yeast

Plus you have almost 2 pounds of crystal malt in there. I would second stpug's idea of throwing a highly attenuative belgian yeast in there. I don't think you'll get much if any belgian character from only a few points drop. I just don't know how well fresh yeast will react to already fermented beer. It's worth a shot though. I don't think the extra S-04 you pitched will do anything though. If nothing else you can just call it a session milk stout at about 3.3%.

 

[GuldTuborg]

Are you taking that 1.028 measurement with a hydrometer or refractometer?

I wouldn't say your efficiency "sucked," but it wasn't high, either. A little lower than average, but that happens. You have a very high percentage of specialty grains and unfermentables, plus a relatively high mash temp, so lower attenuation is to be expected. I still would have expected to get a lot more than more than ~25%.

Oh, nevermind. I mistook your preboil gravity for your OG. You're still under 50% AA, which is low, even if it is much better. I bet this would be good to mix with another, much drier, batch.

 

[WarEagleBrewer]

Ya know, I never thought about the recipe profile having too many specialty grains as opposed to my base malt. I was looking to do a sweet chocolate malt and put together things from a couple different recipes. It looked good in Beersmith..... but I guess that doesn't always mean much. Oh, and the measurements were taken using a hydrometer.

 

[tuskenraider]

Have you calibrated your thermometer lately? Maybe your mash temp was even higher than you thought. I typically get a 1.014 to 1.016 FG with English yeast mashing 154-6 and using lactose.