10 replies to this topic

[earthtone]

do yeast use ergosterols like "higher" multicellular fungi? Do they also use long/short chain fatty acids and differing concentrations of phospholipids in cis formation to maintain membrane integrity like mammals or even bacteria do? And lastly is there a preferential adjustments made depending on whether it is osmotic pressure rather than say temperature and fluidity of the bilayer being combatted by the yeasties??I always here about the importance of sterols, understandably but if yeast also use phospholipids in this way then the main bilayer constituents must also be taken into account (that is phospholipids...)thanks. just curious

[davelew]

The main sterol that yeast use is, in fact, ergosterol.I find it useful to remember how yeast evolved, and then most of the biochemical pathways make more sense. Wild yeast evolved to metabolize drops of fruit juice from rotting fruit. Since drops have such a high surface area-to-volume ratio, oxygen was widely available, so many pathways evolved that required oxygen. At the same time, competing organisms were often around, so to claim the drop of fruit juice for saccharomyces, yeast evolved the ability to lower the pH and produce alcohol, as well as the ability to withstand lower pHs and higher alcohol concentrations than other microbes. Since there's not much fat in fruit juice, yeast never evolved the ability to metabolize fats.I would guess that, since yeast use their ability to withstand osmotic pressure as a survival skill against other microbes, they have the ability to preferentially add robustness to osmotic pressure to their membranes.As for phospholipids, I believe barley has enough phosphates in it that the building blocks for phospholipids are rarely an issue. You hear about sterols becasue sterols are so often an issue; yeast didn't evolve to grow in 5 gallon vats with so little surface area, and we have to trick yeast into thinking they're in a small drop of fruit juice with plenty of dissolved oxygen. The downside to not tricking the yeast is insufficient O2 to synthesize sterols.

do yeast use ergosterols like "higher" multicellular fungi? Do they also use long/short chain fatty acids and differing concentrations of phospholipids in cis formation to maintain membrane integrity like mammals or even bacteria do? And lastly is there a preferential adjustments made depending on whether it is osmotic pressure rather than say temperature and fluidity of the bilayer being combatted by the yeasties??I always here about the importance of sterols, understandably but if yeast also use phospholipids in this way then the main bilayer constituents must also be taken into account (that is phospholipids...)thanks. just curious

[Jimmy James]

A lot of questions earthtone but I am not sure where you are going with this. There is a body of research showing that S. cervisiae utilize sterols as a sort of oxygen sensor. S. cervisiae will also degrade sterol and engage in multiple pathways of oxygen utilization during sterol synthesis with excess oxygen present. From what I've read on the subject sterols are important but just one factor. I think sterols and "oxygenation" are way overblown but that's just my opinion and there's a whole slew of companies selling oxygenation and brewers who've invested in it that will readily disagree.

[denny]

Wow, youse guys are smart! While we're on the subject of yeast, a discussion arose on another board I frequent about the optimal number of reproductive cycles and why. What I've always heard cited is that you want 3 cycles as optimal, but I've never heard why or what happens if that number is exceeded. Thanks for any help you can provide.

[Jimmy James]

Denny, this is one of the more informative papers I've found on the effects of pitching rate and oxygenation. httpss://lirias.kuleuven.be/bitstream/123456...t+al.+2009b.pdfI don't know if you are asking about reproductive cycles during fermentation or prior, so it's hard to speculate.

[denny]

Denny, this is one of the more informative papers I've found on the effects of pitching rate and oxygenation. httpss://lirias.kuleuven.be/bitstream/123456...t+al.+2009b.pdfI don't know if you are asking about reproductive cycles during fermentation or prior, so it's hard to speculate.

Both, really, but the conversation I was referencing was about yeast in starters. Thanks for the link....I'm about to start a long, boring rehearsal so maybe I can look through it then.

[earthtone]

Denny, I'm not sure about the best number of cycles but I will look into it.Jimmy James, I am just curious and understand enough at a cellular level to try and get some more insight if I can. I think you are dead on that sterols are only one component - really a minor constituent of bilayers in general. The question in regard to the phospholipids is linked to my curiosity about other methods of ensuring membrane integrity such as adding olive oil - which contains lipids that can be incorporated directly into a membrane and whether there is a way to provide a maximum potential for the yeast to incorporate (via feeding like with olive oil or something) or synthesize the proper phospholipids for the bucket conditions of fresh wort - as davelew said we are really tricking the yeast and using an evolved trait in a specified and refined way.Since phospholipids make up most of the membranes, and we are worried about membrane health from a viability and especially high gravity brewing POV, I thought perhaps they were being neglected in all this focus on sterol production...kinda the point you were making Jimmy.The reason I am asking these q's is that it may very well be that the yeasties make all the correct phospholipids they need and self-regulate to a point where they only need help with the sterols, but I don't know so I ask!

[dagomike]

I think sterols and "oxygenation" are way overblown but that's just my opinion and there's a whole slew of companies selling oxygenation and brewers who've invested in it that will readily disagree.

Without growth, you're going to have negative flavor issues and lack positive flavors. Yeast growth is good.

What I've always heard cited is that you want 3 cycles as optimal, but I've never heard why or what happens if that number is exceeded. Thanks for any help you can provide.

Intuitively, I'd think with each generation the cells will have more budding scars. I would imagine to the point there would be respiration problems. And of course not able to produce any more yeast.

[dagomike]

The reason I am asking these q's is that it may very well be that the yeasties make all the correct phospholipids they need and self-regulate to a point where they only need help with the sterols, but I don't know so I ask!

I'm not really following what the heck you're saying, but one thought is that yeast can do all sorts of things. The trick is getting them to do what we want for the desired results.

[davelew]

I've been told that after each generation, half the cells only have one budding scar.

Intuitively, I'd think with each generation the cells will have more budding scars. I would imagine to the point there would be respiration problems. And of course not able to produce any more yeast.

[BrewerGeorge]

I've been told that after each generation, half the cells only have one budding scar.

That has to be the case, because otherwise, yeast wouldn't be immortal. (The strain, that is.)