Attenuation question

[Thile]

Hi Y'all. New Brewer here - just a few batches in so far.

I haven't had many problems such as some of the other new brewers have mentioned, really enjoying it so far - labor of love.

I do have a question regarding the attenuation of a couple of stouts that I've brewed. I meant to look at my numbers last night, but I know what they are ball park.

The second batch I did was a Milk Chocolate Stout kit from Norther Brewer. My OG was pretty much right on target (1051). However, the FG was 1.020. I checked it a couple times as I went and it was steady from secondary on so that was a pretty stable number. I searched some on google but wasn't really sure if it was due to the non-fermentables in that kit or just a poor attenuation? I used the WYeast 1332 NW Ale with a starter.

The latest brew I did was the peace coffee stout porter (also from NB). I did add a pound of brown sugar and ended up with an OG of 1052. It had a 'weird' fermentation - did not notice much krausen nor did it 'bubble' out of the air lock for very long. I wanted to make sure it was going, so checked the SG and got 1.020. I haven't had a chance to check it again.
WYeast London ESB 1968, again with a starter, for this one.

While it may be too early to tell on the second, I guess my question is: Is this normal attenuation for the darker beers - stouts and porters? I was expecting my FG to be closer to 1.015 in both cases. I haven't had this same issue with the other kits I've done.

Thanks,

 

[Bensiff]

Assuming you are extract brewing you are going to have higher FG than if you were doing all grain batches. 1968 also attenuates less than something like 1056, so I would consider using a higher attenuating yeast for your extract batches.

 

[smizak]

I've used S-04 and 1968, both similar strains, and those beers always stopped around 1.020. That strain is meant to leave some residual sweetness and floc out real fast. You're all good.

 

[Bru]

If you added lactose it would raise gravity. So would certain malts such as crystal, munich etc - but not by much.
If you're doing all-grain a high mash temp will decrease fermentility (increase FG).
Also - temperature of your sample will affect the reading. For example if you're checking gravity while the wort is hot and then re-checking when its cooled your reading will be out. You either need to cool the sample or adjust for temperature.
You're getting a low +-60% attentuation. Ive recently made an Oktoberfest which went from 1.055 to 1.018 - mashed at 155.

 

[Thile]

Thanks.

I am doing extract. Thought that was inferred but yes those are extract kits from NB. I didn't realize that also made a difference with respect to all-grain.

The Milk Chocolate kit does add 1 lb of lactose and has some of the darker malts.

No worries.

Oh, I take my SG readings at room temperature so haven't really bothered to adjust for incremental temperature readings for the most part. It didn't seem like that was too important for what I was doing.

 

[Hex23]

I've just recently used 1968 and with pretty similar results. I didn't see any info about when you took the measurement. I measured 1 week into primary and got 1.022 (OG 1.059)... then later found that my hydrometer is off by 4 points! After 3 weeks in primary it got down to 1.015, which is 71% AA - as predicted. Seems like a reasonable rule of thumb would be to add 1 point if you're measuring at room temp.

 

[Thile]

I'll check it again, but I first checked the Coffee stout after 5 days because I was not sure if it had fermented (as mentioned on here the only way to be sure is via hydrometer, but I had not seen a fermentation like this before #newbie).

I have to add the coffee this weekend so will either rack it to secondary or keep it on there (usually rack to secondary for space issues; just have the one primary).