[narcout]

The better question is why would anyone rack to a secondary after cold crashing?

After primary fermentation is complete, I cold crash for a few days and then rack into the serving keg which goes into the kegerator for cold conditioning and carbonating.

What I was wondering was whether the yeast would still scrub any oxygen that was introduced at that point.  I rack under pressure into CO2 purged kegs so it isn't much of an issue for me.  I was just curious.

[Joe Sr.]

One of the big reasons why I still use a secondary is that it allows me to crop higher quality yeast.  The yeast cells that are still in suspension at racking time are the least flocculent cells, some of which may be petite mutants.  Carrying these cells over to the next fermentation can have a negative effect on fermentation.

I have experienced exactly this problem with the least flocculent cells.  I have found that after a few generations of harvested yeast, I sometimes wind up with batches that will not clear.

My SOP on harvesting is to swirl up the yeast from the primary and pour into sanitized containers.

No big deal, as they clear with time and gelatin, but sort of PITA.  It lets me know when to get some fresh yeast.

[S. cerevisiae]

I have experienced exactly this problem with the least flocculent cells.  I have found that after a few generations of harvested yeast, I sometimes wind up with batches that will not clear.

That's a major drawback of not being able to draw from the middle layer from a conical when repitching.

Racking can be used to select for flocculaton characteristics.  For example, one can end up with a crop that is more flocculent on average than the original yeast culture by racking early.  If one keeps racking early and cropping from the primary, one can often make the culture progressively more flocculent.  The transformation may not happen in a batch or two, but it will happen because one is cropping the most flocculent cells when one racks early and crops from the primary.

If you have the opportunity to watch a top-cropping brewery in action, you will see that they usually skim and discard the first head, which is known as the "brown head."  The second yeast head is skimmed and used to pitch the next batch. 

[Joe Sr.]

I have experienced exactly this problem with the least flocculent cells.  I have found that after a few generations of harvested yeast, I sometimes wind up with batches that will not clear.

That's a major drawback of not being able to draw from the middle layer from a conical when repitching.

Racking can be used to select for flocculaton characteristics.  For example, one can end up with a crop that is more flocculent on average than the original yeast culture by racking early.  If one keeps racking early and cropping from the primary, one can often make the culture progressively more flocculent.  The transformation may not happen in a batch or two, but it will happen because one is cropping the most flocculent cells when one racks early and crops from the primary.

If you have the opportunity to watch a top-cropping brewery in action, you will see that they usually skim and discard the first head, which is known as the "brown head."  The second yeast head is skimmed and used to pitch the next batch.

Yes.  AFter some serious non-flocculant selection after sequential cropping I've changed to taking one big crop (2nd gen) and using that to build starters for subsequent batches.  So far, better luck.

[majorvices]

But, if you collect yeast in mason jars and shake the jar you should be able to scrape the top layer and get to the middle. Maybe this isn't perfect but it is what I have used in the past with great success. And I usually cold crash on the yeast cake and I can't say I have ever had any problems with this method. That said, I have never gone more than 3 or 4 gens with carboy/bucket yeast harvesting.

Using conicals, it is very nice to be able to select yeast from the middle layer with racking arm.

Mark: If oxidation is not a problem on un filtered beers why is it that on our bottling line at YHB the beers that come off the line mis-capped are set aside and hand capped later and reserved for brewery consumption. And after about 2 weeks there is a definite flavor loss in the mis-capped ones as opposed to the capped ones. I can't understand why this would have any other explanation except that is is oxidation. And this is on a wheat beer with plenty of live yeast in suspension. If having live yeast in suspension was a silver bullet as you assert, you would think that those beers would be just as fresh as the others that are capped on foam a half second later.

All that said, I used to rack my homebrew into unpurged corny kegs before I "knew better" and back then I can't really say I experienced any major problems. I would be really careful on the racking though and purge the head space immediately afterward. If you have a lot of co2 still dissolved in the beer and you rack really careful the co2 coming out of solution should displace the o2 in the head space. But, still, I think it is far better to just purge. After handling hundreds of kegs and thousands of gallons of beer at a working brewing I can truly attest to how important it is to minimize o2 pick up post fermentation at every level. Because, infection aside, oxidation is the number one factor in beer freshness - hands down - even on unfiltered beer. I do believe that yeast in suspension helps to mitigate oxidation, but I do not believe that is is a magic bullet.

[S. cerevisiae]

Mark: If oxidation is not a problem on un filtered beers why is it that on our bottling line at YHB the beers that come off the line mis-capped are set aside and hand capped later and reserved for brewery consumption. And after about 2 weeks there is a definite flavor loss in the mis-capped ones as opposed to the capped ones. I can't understand why this would have any other explanation except that is is oxidation. And this is on a wheat beer with plenty of live yeast in suspension. If having live yeast in suspension was a silver bullet as you assert, you would think that those beers would be just as fresh as the others that are capped on foam a half second later.

I never said that one could go crazy with O2 infiltration after primary fermentation is complete.   What I said is that the amount of O2 that is introduced by racking is insignificant, and the yeast cells that are in suspension will rapidly consume any O2 that is introduced.  There are plenty of reasons not to use a secondary fermentation, but oxidation is not one of these reasons while yeast cells are in suspension.

Without seeing your process and tasting the phenomenon to which you are referring, I do not have a clue as to why you are experiencing a loss of flavor in the mis-capped beers..  Part of the flavor loss could be due to a partial loss of carbonation while the bottle is mis-capped.  If you let samples from mis-capped and properly capped bottles go flat, do they still taste different?

[majorvices]

I think that what a lot of us are saying is that it is best to avoid secondary because it is a chance to introduce o2. Leaky autosiphon sending bubbles down the line. Unintentional splashing. Airlock running dry. Large head space that can't be purged with co2 locked in solution.

I used a secondary all the time without purging with no problems, but that secondary was a keg and I purged the head space. I think at the very least you need to purge the head space.

Regardless, I guess we will have to agree to disagree. My strong feeling is to avoid oxygen pick up whenever possible. But I do agree that an unpurged secondary can be used, if used very carefully to avoid as much o2 pick up as possible.

[narcout]

I was reading the portion of Kaiser's website concerning fermenting lagers, and I came across the sentence below.

"Recent studies have shown that even active yeast may not be active enough to consume all the oxygen from the headspace before it can contribute to oxygenation of the beer [Hermann 2005], because of that the head space should be purged as well."

There's a link to source on Kaiser's wiki, but it doesn't seem to be working at the moment, and I wasn't able to pull it up with a Google search.  Also, I think it is probably in German.  Below is the reference from Kaiser's site:

M. Hermann, Entstehung und Beeinflussung qualitätsbestimmender Aromastoffe bei der Herstellung von Weißbier, Dissertation, Technical University Munich, 2005

[S. cerevisiae]

One of the problems that I see with a using a secondary is processed oriented.  When using a secondary, the secondary fermentation vessel volume has to be less than the primary fermentation vessel volume in order to minimize head space.  Anyone who is fermenting 5 gallons of wort in a 5-gallon carboy and racking to a 5-gallon carboy is more than likely going to end up with significant head space.  I have always fermented a third to half of a gallon more than will fit in my secondary fermentation vessels in order to ensure that the carboy or better bottle is filled at least up to the beginning of the neck as well as to have enough liquid to swirl my yeast crop.

The greatest opportunity for O₂ pickup is before the end of the tubing becomes submerged in green beer.  The air in the carboy is being purged as the carboy is filled via a combination of displacement and outgassing.  Anyone who has used a secondary has noticed that the airlock starts to bubble after it has been affixed. 

With that said, I concur with the use of CO₂ purging as an insurance policy if the use of a secondary fermentation vessel results in a significant amount of head space, especially with the modern tendency to allow a primary fermentation to go a week or more beyond the end of active fermentation. However, there are advantages to using a secondary fermentation vessel that cannot be ignored.  Cropped yeast is healthier.  Dry hopping is more effectively accomplished after the beer has been racked off of the lees.  Bulk aging is better performed in a secondary fermentation vessel or keg than in a primary fermentation vessel.  A secondary fermentation vessel allows for relatively rapid sedimentation of suspended yeast cells and organic matter without the need for cold storage.  This feature allows brewers with minimal investments in gear who are still in the bottling stage to bottle relatively clear beer without having to wait 3+ weeks for the beer to clear in the primary.

[Guenther]

A secondary fermentation vessel allows for relatively rapid sedimentation of suspended yeast cells and organic matter without the need for cold storage.

What's the reason it would make any difference on how fast yeast or anything else would get to the bottom since the beer density is the same?

Guenther

[S. cerevisiae]

What's the reason it would make any difference on how fast yeast or anything else would get to the bottom since the beer density is the same?

The difference in sedimentation has nothing to do with density.  It has to do with the propensity for yeast cells to remain in suspension while the beer is still sitting on the trub.  This phenomenon can be viewed by using transparent primary and secondary fermentation vessels.  For example, less flocculent strains such BRY 96 (a.k.a Ballantine "beer," "Chico," Wy1056, WLP001, US-05 ...) will often take several weeks to sediment after fermentation is complete if left on the trub.  However, most BRY 96 fermentations will clear in a few days if racked to a secondary fermentation vessel after fermentation is complete.

[Stevie]

What's the reason it would make any difference on how fast yeast or anything else would get to the bottom since the beer density is the same?

The difference in sedimentation has nothing to do with density.  It has to do with the propensity for yeast cells to remain in suspension while the beer is still sitting on the trub.  This phenomenon can be viewed by using transparent primary and secondary fermentation vessels.  For example, less flocculent strains such BRY 96 (a.k.a Ballantine "beer," "Chico," Wy1056, WLP001, US-05 ...) will often take several weeks to sediment after fermentation is complete if left on the trub.  However, most BRY 96 fermentations will clear in a few days if racked to a secondary fermentation vessel after fermentation is complete.

What causes this to happen? CO2 pulling up yeast from the cake?

[S. cerevisiae]

What causes this to happen? CO2 pulling up yeast from the cake?

Yes, the phenomenon is more than likely due to outgassing. 

[Frankenbrew]

What causes this to happen? CO2 pulling up yeast from the cake?

Yes, the phenomenon is more than likely due to outgassing.

Very interesting! But wouldn't this yeast will behave the same after packaging (kegging or bottling) as it would in a secondary fermenter?

[S. cerevisiae]

Very interesting! But wouldn't this yeast will behave the same after packaging (kegging or bottling) as it would in a secondary fermenter?

I believe the take away here is that racking off of the primary removes a lot of yeast from the equation, which allows a large percentage of the cells that are still in suspension to naturally settle out of suspension.  The result is fewer cells going into bottling, which, in turn, results in less sediment in one's bottles.  The same thing can be accomplished via forced sedimentation.  However, my experience shows that natural sedimentation tends to lead to a product that needs less aging to round off the harsh edges.