Compressed Air As Opposed To Co2

[Thirsty Boy]

. . . . . I think I agree with SJW here. My understanding is that it is the presence of sugars AND oxygen that will switch the yeast back to reproducing mode. The majority of oxygen will have been metabolised by the yeast within the first few hours after pitching for sterol synthesis. The most important sterol is ergosterol (can be over 90% of total sterol) and to quote Brewing Science & Technology, Brewers Yeast "the final reaction that produces ergosterol requires molecular oxygen". And from Briggs - Brewing Science and Practice - "In the yeast crop obtained at the end of fermentation, sterol and unsaturated fatty acid levels are reduced to growth-limiting concentrations, hence, the need for oxygenation of wort in the next fermentation". I think the important point here is not that more yeast is being created in the keg but that fermentation is kicked off again by the yeast still present in the beer. A final quote from Handbook of Brewing - Chpt 10 which may answer your question Mark "When a brewer's yesat is grown anaerobically, it accumulates sterols and unsaturated lipids within the cell in excess of the yeast's minimum requirements and the lipids can be "diluted" to a degree by subsequent growth without negative effects. As a result, cells preparad aerobically can grow to some extent anaerobically. However, if yeast is harvested at the end of fermentation and used to inocculate a second batch of wort, then oxygen is required because the new inoculum contains no reserves of the necessary lipids"

RDWHB

Unless they are terribly unhealthy and simply lack the internal resources, or the level of alcohol is too high for them, yeast will reproduce to sufficient levels to ferment available sugars. Regardless of the level of 02. They probably wouldn't have enough resources to go all the way through a batch from scratch without extra 02... but enough for bottle conditioning? Yes they can and do reproduce. I could quote theory, but I don't have too, I have a practical example.

I sometimes filter into bottles and then prime the bottles. The filter removes almost all the yeast, but a very few (probably newly budded and therefore small enough to slip through the filter pores) cells do get through. These reproduce sufficiently to carbonate the beer and leave a very minimal layer of sediment in the bottle. I know its not just the yeast that made it through the filter, because when I filter into a keg, force carbonate and CP fill bottles... there is no visible sediment at all.

Perhaps I get a little 02 into solution during the bottling phase... but certainly not a lot, I am pretty careful about it and I purge bottles with C02 etc. Definitely no more than the average brewer would get in transferring into a keg to be primed for carbonation. So you would certainly get an amount of sediment in a naturally primed keg, presumably at proportionally the same levels you would get in a bottle conditioned beer. Fine if the keg is going to stay undisturbed in your keggerator and can settle for a long time, couple of pints on the garden and it will run clear ... not so great if you need to move it about the place or take it to a party or something.

Probably worth maybe a teaspoon of sugar in even filtered & force carbed kegs... just so that any yeast present try to grow and scavenge up any O2 that would otherwise go towards staling the beer.

 

[masculator002]

I can't see how you would get any more yeast in the keg by priming the keg. There should be little o2 in the beer for yeast reproduction

how do you think you end up with yeast in the bottom of your bottles after a secondary fermentation?????

 

[Darren]

Not sure if this is mentioned or relevent to this discussion but, alcohol production is entirely reliant on anaerobic conditions (ie. no oxygen).

As for the cask ales, I agree with Post Modern, they are not force carbonating the cask so the only oxidation that would occur is at the surface.

Pumping any amount of O2 into beer is bad if you wish to hang on to it for a while. Oxygen causes oxidation (similar to rust of metal) once it starts it never stops.

cheers

Darren

 

[MHB]

masculator002 Posted Today, 07:21 PM
QUOTE (SJW @ Mar 19 2008, 10:23 AM)
I can't see how you would get any more yeast in the keg by priming the keg. There should be little o2 in the beer for yeast reproduction


how do you think you end up with yeast in the bottom of your bottles after a secondary fermentation?????

Thats yeast that was in suspension settling out; when beer is cask clear (i.e. appears clear to the naked eye) you still have 5-10 thousand yeast cell/millilitre of beer.

Thirsty Boy Posted Today, 01:19 PM
sometimes filter into bottles and then prime the bottles. The filter removes almost all the yeast, but a very few (probably newly budded and therefore small enough to slip through the filter pores) cells do get through. These reproduce sufficiently to carbonate the beer and leave a very minimal layer of sediment in the bottle. I know its not just the yeast that made it through the filter, because when I filter into a keg, force carbonate and CP fill bottles... there is no visible sediment at all.

I think in this case the yeast has settled out in the keg, and you arent transferring it to the bottles.
Good enough observation but not a causal argument.

MHB

 

[SJW]

I once thought this too, but yeast can apparently reproduce anaerobically. I understand it extracts the oxygen it needs from other molecules using energy stored from conventional fermentation.

Well have u primed a keg with sugar? and what was the results?

Thats yeast that was in suspension settling out; when beer is cask clear (i.e. appears clear to the naked eye) you still have 5-10 thousand yeast cell/millilitre of beer.

Thanks Mark. We was only talking about this the other day.

Steve

 

[kook]

It will never carbonate at all which leads to another problem the huge amount of sediment you will get if you are priming a keg like a bottle. save yourself a lot of heartache time and money which would be wasted by cahsing a pipe dream and get what you know is right from the word go, after all you will end up doing it anyway and at the end of the day you know it is safe for use with food stuffs and beverages.

I've done this with english beers (highly flocculative yeast) and you only have a cloudy pour for the first pint or so. After that the remaining yeast clings to the round base of the keg, and won't shift till you pour the final pint (or stir up the keg).

I use a fire extinguisher without any issues. There is no "fire retardant" in a CO2 extinguisher. So long as you buy a new one and it is properly cleaned, there is no issue whatsoever. It's a hell of a lot cheaper, and the CO2 is supposedly filled from the same bulk tank as the food grade CO2.

 

[Thirsty Boy]

Thats yeast that was in suspension settling out; when beer is cask clear (i.e. appears clear to the naked eye) you still have 5-10 thousand yeast cell/millilitre of beer.



I think in this case the yeast has settled out in the keg, and you arent transferring it to the bottles.
Good enough observation but not a causal argument.

MHB

well, except for the fact that its usually all happening about 5 minutes after I've spent half an hour shaking the bejeezus out of the keg. No, I'm talking about diamond bright, just been through a 1 micron absolute filter, very very clear beer. You can leave that keg standing there for a month and there still isn't sediment on the bottom of it, same for CP filled bottles from the freshly shaken keg. BUT - put beer through the same filter into a bottle and add some priming sugar, and there is a very light, but present layer of yeast. Which either appeared by magic... or reproduced from the minuscule quantities that made it through the filter.

I don't believe in magic.. but I do believe that was a causal argument. Or near enough to one for government work at any rate

TB

 

[MHB]

TB

Rather than shoot from the lip I went and did a bit of digging, from what I can find looks like we are both partly right and wrong.

Yes some yeasts can reproduce anaerobically, but this summed up the situation best:-

Brewing yeasts do not develop respiratory competence under the conditions encountered in fermentation. Thus, in the aerobic phase of fermentation, respiratory pathways are repressed because of the presence of sugars. In late fermentation when the sugars have disappeared and their repressing effects are relieved, anaerobiosis prevents the induction of the respiratory enzymes.

The majority of yeasts require oxygen for growth. In a study of type species from 75 genera, it was noted that only 23% could grow under anaerobic conditions on a complex medium supplemented with ergosterol and a source of unsaturated fatty acids (Visser et al., 1990). Of these, S. cerevisiae was exceptional in that it was capable of rapid growth at low oxygen tension. Nevertheless, none of these yeasts, including S. cerevisiae, can grow under totally anaerobic conditions unless the medium is supplemented with a source of unsaturated fatty acids and sterols (Andreason and Stier, 1953 ab). These essential metabolites can be assimilated from the medium or synthesized de novo from carbohydrates. Synthesis requires the presence of molecular oxygen. Both of these are present in wort at the start of fermentation.

Brewing Science and Practice; Dennis E. Briggs, Chris A. Boulton, Peter A. Brookes and
Roger Stevens P 457

If you filter to 1um obviously as you observed you are removing all the mature yeast. I suspect that when you force carbonate, pressure prevents the yeast from further development; so the cells remain small and invisible to the naked eye.

When you bottle condition the low initial pressure and the presence of food (priming sugar) allows the yeast to mature.

My best guess is that there is the same population but in one case the yeast is just bigger.

This has always been one of those questions that bugs me - if you have further information I would like to look at it, please e-mail (address in footer).

MHB

 

[Darren]

TB,

Seems to me you are once again being pedantic about a miniscule point but have missed the obvious. You DID add oxygen at bottling. Maybe you think it was "hardly any" but the fact remains your bottle contained ~21% oxygen before you added the beer. No matter how much you purged your bottle oxygen would have been included, let alone how much oxygen was dissolved in your priming sugar.

cheers

darren

 

[oldbugman]

Can I hook my kegs up to the tail pipe of my car and let the carbon emission fairies do the rest?

 

[Whistlingjack]

TB,

Seems to me you are once again being pedantic about a miniscule point but have missed the obvious. You DID add oxygen at bottling. Maybe you think it was "hardly any" but the fact remains your bottle contained ~21% oxygen before you added the beer. No matter how much you purged your bottle oxygen would have been included, let alone how much oxygen was dissolved in your priming sugar.

cheers

darren

The increase in temperature of the beer, even by a few tenths of a degree, during bottling will force CO2 out of solution. Any oxygen that is in the bottle will be driven to the top. Unless the bottle is disturbed during conditioning, it will remain there.

WJ

 

[Darren]

WJ,

Would be hard not to disturb a bottle at the HB level.

What about the priming sugar??

cheers

Darren

 

[milpod]

Unfortunately,when it comes to co2, they have us by the short and curleys.

Looked into every option,including 22kg lease and refill gear.

After a few hours reading,I decided I'd rather pay.My life is far more important then a few $.

Swap and go for co2 would be sweet,evetually it will happen.

Ok a population of 25 million,it wont.

 

[Whistlingjack]

WJ,

Would be hard not to disturb a bottle at the HB level.

What about the priming sugar??

cheers

Darren

I'm talking about the time after the bottle is filled. I added the sugar to the bottle, then the beer, then capped.

I inverted the bottle afew times then stored it upright. As O2 is the lightest gas, it will rise and occupy the top section of the headspace. Leave the bottle alone and there will be no mixing of gases.

WJ

 

[sathid]

I think diffusion would cause you some problems there mate.

You are saying that after the bottle has been capped, that you will have a layer of CO2 under a layer of O2 right?

Well the concentration difference in the two layers will mean that well before you open that bottle, you will have a pretty much heterogeneous mixture of O2 and CO2, and no layers.

 

[Stuster]

As O2 is the lightest gas, it will rise and occupy the top section of the headspace.

Not how it works, WJ. In a bottle headspace (or any space come to that) you'll get an even distribution of all gases occurring over time. Gases mix, despite any differences in their atomic mass. That's also true for the old chestnut of CO2 sitting blanket-like on top of your fermenting beer. <_<

 

[SJW]

I think diffusion would cause you some problems there mate.

You are saying that after the bottle has been capped, that you will have a layer of CO2 under a layer of O2 right?

Well the concentration difference in the two layers will mean that well before you open that bottle, you will have a pretty much heterogeneous mixture of O2 and CO2, and no layers.

Please! :angry:

 

[sathid]

please what?

 

[Thirsty Boy]

TB,

Seems to me you are once again being pedantic about a miniscule point but have missed the obvious. You DID add oxygen at bottling. Maybe you think it was "hardly any" but the fact remains your bottle contained ~21% oxygen before you added the beer. No matter how much you purged your bottle oxygen would have been included, let alone how much oxygen was dissolved in your priming sugar.

cheers

darren

Of course I get added 02 at bottling. Not much, because the bottles are carefully purged with C02 and the sugar is dissolved in water and boiled, thusly driving out the majority of the oxygen... but indeed, some 02 would be introduced.

Of course if you read my post carefully you would have noticed that I qualified the whole point by comparing it to the amount of 02 that would be taken up in process of transferring to a keg and said rather than that I get no 02 pick-up, but that its most likely to be less than the amount most homebrewers pick up in transferring to a keg. So the levels of oxygen in the containers I was observing would be less than or equal to a keg and inferences about yeast behavior in a low oxygen environment would be comparable in the two situations.

Strangely enough having worked in the brewing industry for 17 years... I actually do know some of the mechanics of controlling 02 pick-up in the brewing process and took them into account before I posted. But thats beside the point, I'm sure you'll notice something else obvious that I missed.

MHB - nice stuff there. I suspect once again that you are fairly close to the mark. The immature cells reaching maturity plus a limited amount of reproduction - both aerobically from the inevitable amount of o2 ingress that Darren pointed out and some limited anerobic growth from residual sterol levels within the cells and fatty acids etc in the beer. All of them adding up to the fine layer of yeast I observed.

Thanks Mark, I learned something from your post.

Thirsty

 

[SJW]

please what?

Please stop talking shit