I scoured town looking for some fructose for my rib rub today. Didn’t find any, but I came across some trehalose, for about $2 per pound. Wondering if it has any practical applications in homebrewing. If not as a fermentable, maybe to add to starters for harvested yeast, or something along those lines?
The Internet at says S. cerevisiae can ferment trehalose. It’s a disaccharide of two glucose molecules.
Might it be useful if you’re starting fermentation with a yeast that does not have good stores of energy reserves? Those are made up by glycogen and trehalose, and are used - mainly the glycogen - for fueling the processes during the lag phase, especially the uptake of oxygen, and the synthesizing of sterols. Trehalose, I think, is more important for handling stress situations - and maybe it could be used instead of glycogen if glycogen is missing?
But this would suppose that the yeast in this situation could take it in, which is not the same, I guess, as mobilizing if from internal storage. I’m no biologist, and I really do not know. I only know that these processes are fairly complicated, involving producing the right enzymes.
Well, probably this would have been well known if it was possible:).
Thanks for the reply.
a yeast that does not have good stores of energy reserves
What kind of yeast would we be talking about here? A harvested yeast? A liquid yeast that’s past its expiration date? A kveik that’s been dried? A yeast that’s been repitched from a hard seltzer?
Whenever yeast is stored without access to nutrients, it will need to draw on it’s internal stores of energy to keep alive, and they consist mainly of glycogen. It’s also got trehalose stored, but as I understand it, that is mostly mobilized in stress situations.
Glycogen stores are built up when the yeast senses that nutrients in the environment are getting scarce, and it prepares for dormancy - much like a bear who is sensing the onset of winter and hibernation. So at the end of the fermentation of a brew, that is what occupies our yeast, and when fermentation is finished, the glycogen stores should be at their highest. But they will immediately start going down, like your bank account when you lose all income.
Lucky yeast will then find itself in a welfare state, i.e. your brewery, where it will be taken care of so that it won’t have to starve to death. Unlucky yeast dies after a while, when there is no more glycogen left.
Apart from keeping the yeast alive during starvation periods, the glycogen is needed when lucky yeast once again find itself immersed in a sugary solution, hopefully saturated with oxygen. It then needs the glycogen to fuel an intense period of synthesizing cell membrane raw materials, i.e. sterols. Lacking glycogen (and oxygen) it won’t be able to build full stores of sterols, and that means it will not be able to multiply efficiently, which again means it will have trouble fermenting your wort efficiently, and make good beer for you. Serves you well for maltreating your yeast.
If you use dried yeast, you don’t have to worry about anything at all. You just have to remember adding it to your wort. And if you use kveik - I have no idea why anybody would want to do that, but I guess it takes all sorts (I’m a Norwegian, by the way:)) - you need to worry even less, because nothing can kill kveik. You just scrape a 300 year old dried sample from a barn rafter, and you’re set to go.
Low glycogen stores becomes a problem mainly when you are reusing yeast, because they are reduced fairly quickly. At the same time the viability also is reduced, i.e. the percentage of living cells go down. Now you can make beer with yeast that is not at it’s best, but if you want to make the best beer you can make, you should adhere to best practices here, I think. And what all pro’s say, is that yeast should be reused within a few days from end of fermentation, not more than a week after, and definitely not after more than two weeks. (You should not count this from harvest date, as the yeast starts going down as soon as it’s entering dormancy, and you may harvest both days and perhaps even weeks after that.)
Liquid yeast after expiry date may still be OK. I think the yeast laboratories have developed methods that keep yeast fresh much longer now than what was possible only a few yeasr ago. But much depends on storage conditions, so I would make a starter anyway. (But if you do: Take care not to let it spin after the sugar has been consumed. Then you let it start depleting it’s stores again. Better take it off and let it sit quiet a little while before it has gone all the way.)
If you suspect the yeast has got low stores of glycogen, you should administer help in the form of a refreshing/revitalizing starter. Give it some 1.020’ish wort - say a quart/a liter - or so to what you would normally harvest from a 20-25 liter brew. Do not shake it; the less oxygen you get into it, the better. This should sort of mimick the conditions towards the end of fermentation when glycogen stores are built up. NB! This is not a “vitality starter”, which aims to give you yeast that’s alive and kicking and ready to start fermenting your wort right away without adding oxygen to the wort. You might want to make one of those after you’ve revitalized your yeast - or you might use your revitalized yeast in the ordinary way, which means you decant it and add it to a well oxygenated wort.
Yeast that’s been used to make hard seltzer should not, I think, be used to ferment beer. It will not be able to consume maltose and maltotriose, as it will have switched off the genes that code for producing the necessary enzymes. (Making beer is really all about enzymes!). As I understand it, it will eventually come 'round to it, but it will take time, and you’ll get a far from ideal fermentation. You might perhaps be able to “rehabilitate” it, but I really know nothing about that.
Great post, Finn.
Thanks :)!
I guess it was the kveik-part you liked ;).
I certainly liked that part