[Kaiser]

I just posted a write-up on comparing a bottle of Doppelbock that was bottles w/o yeast and one that was bottled with yeast:

The effect of yeast on the flavor development of Doppelbocks

The idea for this experiment came from an online discussion that we had either here or on the NB forum.

Here is the conclusion:

Conclusion:
The result of this tasting did surprise me yet supports my thinking that the hallmark flavor of German Bocks and Doppelbocks is in fact the product of oxidation and staling of the beer. It is assumed that the yeasted beer sample did not exhibit that flavor as strongly since the yeast was able to scavenge the oxygen that had been introduced during the bottling process.

The added yeast did not affect the head retention negatively in this case. One way it can do this is by releasing excessive amounts of Proteinase A into the beer which can break down foam proteins.

The pH was not negatively affected either which is a sign that there was not an excessive amount of yeast autolysis or not enough yeast to make a difference.

The idea that big dark beers benefit from small amounts of post fermentation oxygenation has also been brought up by fellow home brewer Fred Bonjour and warrants further investigation into optimal oxygenation rates ad well as aging times.

[a10t2]

Thanks for writing this up, Kai. The first doppelbock I brewed (and kegged) was fantastic, but the next year's batch (identical recipe, but bottled) just didn't have quite the same "pop". I'd wondered if some aspect of yeast metabolism could explain the difference, and this would seem to confirm that.

It would be really interesting to see what the difference was on, say, five one-gallon batches that had different amounts of oxygen added before force-carbonating. If I could get some blind tasters to evaluate them I'd be willing to brew those beers, although I'd have to get an oxygenation setup first. Do you have any idea what sort of oxygen concentrations would be needed?

[Kaiser]

I think the amount of oxygen we are talking about here is very small. Too small to be measured with the O2 meters some of us have. Varying amount of headspace or various levels of bottle purging could be one approach.

Fo the Dopprlbocks that you mentioned, could there have been a difference in O2 uptake post fermentation? Were they bottle conditioned?

Kai

[a10t2]

I think the amount of oxygen we are talking about here is very small. Too small to be measured with the O2 meters some of us have. Varying amount of headspace or various levels of bottle purging could be one approach.

That's what I was worried about. I was thinking that maybe a reasonably accurate regulator on an O2 tank might be enough. 5, 10, 15 mL/L, etc. Rather than relying on a DO meter.

Fo the Dopprlbocks that you mentioned, could there have been a difference in O2 uptake post fermentation? Were they bottle conditioned?

The second was bottle conditioned, with added yeast after about three months lagering. The first was kegged right out of the secondary/lagering carboy. Otherwise the beers were as identical as I could make them.

The whole reason for bottling the second batch was that everyone loved the first. Most people I distributed the bottles to didn't say anything, but there were several experienced brewers/tasters who said the bottle-conditioned batch was missing "something" the first had had. Granted, no one tasted them side by side, but these are people whose opinions I trust.

[pyrite]

Kai, Interesting experiment, I always wondered about these specifics. I have a few questions.

1.Attenuation delta.  Is this the attenuation that took place after bottling?
2. Which beer do you prefer for smoothness or are you looking for Hallmark flavors, non-yeasted or yeasted?  
3. If other people have done a side-by-side comparison which do they favor?
 

[MDixon]

Interesting, but I believe your experiment needs to run much longer. I'm doubtful as to the amount of oxidation which would occur in a short time frame. Also might want to do a triangle test to see if you really can tell a difference (probably can, due to the difference in attenuation if nothing else).

Some doppelbocks seem to last much better than others. I once aged a bottle of Paulaner Salvator and it was stale, lifeless and a drain pour a few years later and at the same time a bottle of Ayinger Celebrator showed no ill affects of aging. Some interesting research would be to see why Salvator bites it when aged and Celebrator does not

[Kaiser]

That's what I was worried about. I was thinking that maybe a reasonably accurate regulator on an O2 tank might be enough. 5, 10, 15 mL/L, etc. Rather than relying on a DO meter.

The good and bad thing about this experiment is that it can be done at bottling time and you don’t need to brew multiple batches. This also means that you have to measure very small amounts of O2 and add them to the beer w/o them being pushed out by escaping CO2. What I may try next time is purging some bottles with CO2 and in addition to that add yeast to some of the beers bottled in purged and to beer bottled in unpurged bottles.

The second was bottle conditioned, with added yeast after about three months lagering. The first was kegged right out of the secondary/lagering carboy. Otherwise the beers were as identical as I could make them.

This could very likely be a case where you saw the same effect. You may want to brew this beer again and, if you have the means, repeat the experiment  I did. With means I mean being able to bottle carbonated beer, even if it is just with the picnic tap beer gun from a cold conditioning keg.

Kai, Interesting experiment, I always wondered about these specifics. I have a few questions.
1.Attenuation delta.  Is this the attenuation that took place after bottling?

I should make a note of this. The attenuation delta is the difference between attenuation limit (wort fermentability) and attenuation of the final beer. This difference indicates the amount of residual fermentable sugar and plays a big role in the character of the beer. More so than the actual attenuation number. At least that has been my experience.

2. Which beer do you prefer for smoothness or are you looking for Hallmark flavors, non-yeasted or yeasted?  

Another point I missed. I did prefer the non-yeasted sample because of its better flavor profile. However, the yeasted sample was a bit drier and one complaint I have about this Doppelbock is that its FG was a bit high and I’d like it to be a bit drier.  Next time I brew it I’ll fix this.

 

Interesting, but I believe your experiment needs to run much longer. I'm doubtful as to the amount of oxidation which would occur in a short time frame.

I think sufficient oxidation can occur within that time. I don’t have a way to prove that it is oxidation that causes these flavors but I also got similar flavors from a Pils that I oxidized on purpose (adding pure O2 to the head space) and force aged at 70C for a few weeks.

Also might want to do a triangle test to see if you really can tell a difference (probably can, due to the difference in attenuation if nothing else).

The problem here is that I did not prepare enough yeasted bottles for this experiment. I only made 3. One pair I may bring to a home brew club meeting and the last pair I plan to have next year when I do my Doppelbock vertical tasting in March. But I also did not expect these results and will prepare more yeasted samples next time.

Based on comparative tastings I have done in the past this difference seems to be large enough that I could pick it out in a triangle test. I did not have to look for it.

I doubt that it is the attenuation. Though I noted that one sample was drier than the other the difference was not all that great it was something I had to look for.

Some doppelbocks seem to last much better than others. I once aged a bottle of Paulaner Salvator and it was stale, lifeless and a drain pour a few years later and at the same time a bottle of Ayinger Celebrator showed no ill affects of aging. Some interesting research would be to see why Salvator bites it when aged and Celebrator does not

This is very much possible. Salvator seems to be a dark Munich only beer while Celebrator has a more complex grist. My grist should be closer to Celebrator than Salvator.

I do think that this technique may work for some beers and will ruin others. In addition to that I have not shown if the addition of yeast simply pushes out the flavor peak of the beer.  I.e. in 6 months the non-yeasted sample may be past its prime while the yeasted sample is starting to peak and may even become the better beer.

All-in-all, definitely worth some closer observation. Fred has a similar story about oxidation that he was very happy to share with me at the HNC.

Kai