Lager Fermentation Trouble

[gluepot]

Hi everybody. I'm hoping that someone can help me figure out what I'm doing wrong with my lager fermentations. This is my third failed attempt. Here's what happened on my most recent batch (a munich helles from Brewing Classic Styles).

The hot side of the batch was good: 75% efficiency(all grain), 90 min boil, good cold and hot break. The only possible bad thing that happened was I ended up transferring some trub over to the fermentor, although most of it was left in the pot (using Jamil's whirlpool chiller). (I don't think this is the cause of my problems) I chilled down to about 45 and pitched yeast from a decanted 2.5 Liter starter on a stir plate (estimated to be around 350 billion cells), after oxygenating the wort

I oxygenated with pure O2 at 1.5 Liters/min for 120 sec. (I think the 120 sec may be the culprit, more on that later)

Fermentation started within 12 hours, and was very healthy as far as I could tell. Gradually over the course of a week, I brought the temp up to about 55. Bubbling was infrequent at the one week mark. At two and a half weeks it was well done with bubbling and was quite clear, so I racked into a keg and tested the beer. It attenuated fully (1.048->1.011) and was already almost crystal clear. However, It tasted quite bad!

It had a rubbery and perhaps buttery flavor, leading me to think of diacetyl. However, the beer spent a good week at around 55 and I started the fermentation quite cool all with the aim of minimal diacetyl production. To me the beer tasted exactly like my starters do coming off the stir plate, leading me to believe that I over did the O2.

I'm still trying to dial in my O2: going at 60 sec at 1L/m gave me attenuation problems in previous batches, and 90 sec at 1.5L/m seems to do well for my Ales. I figured sense I had a lot more yeast in my lager ferment, I would need more O2, however, I forgot to account for the fact that O2 dissolves more easily at the low temps of the lager. At least this is my guess as to what went wrong. What do you guys think? Does this seem like a reasonable evaluation? I can't think of anything else.

For now I will lager the beer for a month or so and see what happens.

 

[StoneHands]

Helles is a little more water dependent, have you looked at that?
Butter I'd be thinking diacetyl too though. I wouldn't think it's the O2, but I could be wrong. I would think if you supersaturated with O2, not only would it be used by the yeast, a lot would come out of solution early in fermentation.
This is a bit tough to pin down, I'd give it time to lager and taste it again. Lagering has always had a huge effect on the final taste of mine, but they've never truly tasted bad going into lagering either.

 

[AmandaK]

Diacetyl is my bet.

It can present as a buttery taste or a slick, oily palate. Fermenting at low temperatures increases this natural product of fermentation because higher temperatures (67*-70*, not 55*) allow the yeast to clean up their own nasties.

Adding too much O2 is not your problem. There have been several studies that show an upper limit to how much O2 you can actually get into wort. Also, O2 would usually only be a problem if you oxygenate AFTER fermentation begins.

If I were you, I would to a PROPER diacetyl rest, at 67*-70* for 2-3 days and then transfer to lager. Remember that diacetyl is produced by all yeasts (in varying amounts, of course) and the best way to get rid of it is to keep it on the yeast and warm it up to ale temps to allow the yeast to clean it up.

 

[Yooper]

Agreed. While you may not always need a diacetyl rest, doing one as a matter of course is good practice if you've had any diacetyl issues. Some yeast strains produce more diacetyl than others. If you're not expert at recognizing diacetyl in small amounts (it presents as a "slick" or oily feeling on the tongue in small amounts), then doing a diacetyl rest at the end of primary would be a good practice.

With time, a tiny bit of diacetyl before lagering will get worse and can turn into a butter bomb after lagering and it's tough to fix. Sometimes krausening can help, but it's better to prevent the problem in the first place.

The 02 is NOT the cause. The cause is simply the yeast didn't get a chance to clean up the diactyl.

 

[gluepot]

What I've read is that low temps initially in the ferment reduce the precursors of diacetyl, sometimes even rendering a diacetyl rest unnecessary. However, maybe for some reason I do just have diacetyl in abundance in my batch, and I needed a higher temp D rest. I will try this next time. Thanks for the suggestion.

I'm still not convinced that the o2 is not part of my problem. I'm sure there is an upper limit to o2 absorption in wort, it is just a matter of how high that limit is(especially in cold wort). Over oxygenating with just air is tough if not impossible, but with pure o2, I expect it is quite possible. The thing that makes me suspect this so much is that my beer tasted exactly like starter wort off a stir plate. Very rubbery is the only descriptor I can think of.

My water is pretty low in minerals and I filter and dechlorinate. I add some calcium for yeast health, and treat my mash with lactic acid to adjust ph. I think my water should be pretty good for a helles.

Thanks for the comments.

 

[gluepot]

Or maybe it's just diacetyl I'm used to tasting in my starters? I will definitely try a warmer D rest next batch.