Low oxygen/fermentation

[bbksv]

I have about 6 brews under my belt and the last couple I switched over to an O2 stone with oxygen to aerate. The last couple batches have had issues getting under 1.020 fg and I think it is due to me not running the oxygen long enough...20-30 seconds. So with my last batch..it is still in the fermentor and sitting at 1.020 ( OG Was 1.054)...is there anything I can do to push it down a little more if it was due to low oxygen? It is a milk stout so I know the lactose would keep it a little high and the final temp was about 74 so cant raise the temp any more

 

[mredge73]

Do not add oxygen at this point, oxygen should be avoided at all costs.
You should have plenty of yeast, gentle stirring will rouse them back into solution and may drop it a few more points. Be careful not to splash.

I don't think you have a O2 problem, you have something else going on. You will have to share more about your process if you want help getting to the bottom of the problem.

 

[bbksv]

well the first of 2 batches I used liquid yeast..made a starter and pitched the whole 2L starter. It was fermenting within 2 hours and was banging away for 2 days then stopped. My OG was low on that one..I am assuming since I pitched the whole 2L starter. I will decant for future batches. For the second batch it was 1.054 OG and I pitched S-04..fermented for about 3 days. 10 days later it is sitting at 1.020 and hasn't moved. Neither batch was too hot or cold..had plenty of yeast. The only thing in common was that I started using the O2 stone...but now that I read in to it they all recommend aerating for atleast 40 seconds stirring around. I just stuck the stick in and ran it for 20-30 seconds which I think isn't adequate.

I am about to brew another stout so I will aerate for 45 seconds while stirring the stick and see how it goes.

 

[McKnuckle]

The lactose is probably adding more gravity than you thought it would. How much lactose in how much of a batch size? I also highly doubt the O2 treatment or lack thereof is a significant factor. I never use an O2 stone. I either shake my primary for 10 seconds, or rack carelessly (splashing) to the fermenter. But I never use pure O2, and my FGs are always in a normal range.

 

[bbksv]

I added 1 ob of lactose in a 5 gallon batch but that was during the boil so my OG was including the lactose...so while I would expect lactose to keep the FG up a little I would think I can attenuate to lower than 4.4% abv. The first batch was only like 3.8%.

 

[Gnomebrewer]

A few things.....

Not having enough oxygen won't stop the yeast from fermenting, it just makes the ferment slower and more sluggish (which can cause pH issues and off-flavours from gases that aren't blown off). You might finish a point or two higher, but not much more than that.

S-04 is a dry yeast, which (according to the manufacturer) doesn't need oxygen anyway.

Adding oxygen later in the ferment will (apart from oxidising the beer) cause the yeast to respire instead of ferment. They prefer to breathe like we do when there's oxygen available (and subsequently not make ethanol)!

A pound of lactose adds about 7 points of gravity to a 5 gal batch. It is completely non fermentable, so also adds 7 points to the final gravity! So, without the lactose, that was 1.047OG to 1.013FG which is quite reasonable.

 

[JoeNavy]

I have about 6 brews under my belt and the last couple I switched over to an O2 stone with oxygen to aerate. The last couple batches have had issues getting under 1.020 fg and I think it is due to me not running the oxygen long enough...20-30 seconds. So with my last batch..it is still in the fermentor and sitting at 1.020 ( OG Was 1.054)...is there anything I can do to push it down a little more if it was due to low oxygen? It is a milk stout so I know the lactose would keep it a little high and the final temp was about 74 so cant raise the temp any more

Typically this is a yeast issue. As you said in your post, the yeast starter yielded a more efficient fermentation. Obviously, starters can be great helps in terms of vigorous fermentation and getting it started early (as implied by the name). However, there are a lot of things that go into your process. What do you ferment with? Are there any leaks? What type of yeast did you use? Are you using temp control? Each yeast in its own has the appropriate range for gravity depending on the batch. For example, 1 package of WLP001 is meant for beers with a 1.048 gravity and below. Anything greater and you run the risk of missing your FG on the high side. If you have adequate yeast, it must be 100% healthy for 100% attenuation. If you are dry hopping, ensure you have done so in the appropriate range (typically within 12 days of brewing) to allow for the presence of a CO2 blanket to avoid adding oxygen to the mix.

Anyways, fill in more details and we can see what exactly is your issue!

 

[Cavpilot2000]

I know it's well past relevant for this particular batch, but you could also add a secondary yeast that is more attenuative, even going into wine or champagne yeast territory. They MIGHT chew away a few more points.

 

[Shrimp]

I know it's well past relevant for this particular batch, but you could also add a secondary yeast that is more attenuative, even going into wine or champagne yeast territory. They MIGHT chew away a few more points.

Champagne yeast goes for simple sugars, which are probably long gone. It can't metabolize more complex sugars, which is what's likely left.

A 1.020 on a beer with a pound of lactose with that yeast doesn't seem out of the ballpark.

I've never heard about dry yeast not needing oxygen - probably something I would ignore.