Wyeast smackpack & yeast starter

[sjbeerman]

Yeah, I've gotten that far with my casual research, too...but how does it play out? Usually, we talk about stress factors as a bad thing. Why is trehalose good?

Ok MalFet, now you really got my wheels turning so early this morning.

Ok, we know that both glycogen and trehalose are important in brewer's yeast. However, here is where they differ and why it appears that trehalose becomes an important factor in yeast metabolism. Glycogen provides energy for cell maintenance during storage. Trehalose has two functions: a storage reserve and stress protectant (as previously mentioned). It's protective against osmostress and ethanol stress. So why is this needed or why is it good? A study was done where the trehalose concentration was measured after 24 h after pitching the yeast in a normal gravity, high gravity, and a very high gravity wort (> 22 P). They found that the amount of trehalose in the very high gravity wort was higher than the other two worts. Therefore, under conditions of stress (i.e., high ethanol content), the yeast metabolism is allowed to continue due to the built up trehalose concentration. This is basically my understanding of what is going on here...

Reference: Blieck, L. et. al., Isolation and Characterization of Brewer's Yeast Variants with Improved Fermentation Performance under High-Gravity Conditions, App. and Environ. Micro., 2007, 73(3), 815-824.

 

[MalFet]

Ok MalFet, now you really got my wheels turning so early this morning.

Ok, we know that both glycogen and trehalose are important in brewer's yeast. However, here is where they differ and why it appears that trehalose becomes an important factor in yeast metabolism. Glycogen provides energy for cell maintenance during storage. Trehalose has two functions: a storage reserve and stress protectant (as previously mentioned). It's protective against osmostress and ethanol stress. So why is this needed or why is it good? A study was done where the trehalose concentration was measured after 24 h after pitching the yeast in a normal gravity, high gravity, and a very high gravity wort (> 22 P). They found that the amount of trehalose in the very high gravity wort was higher than the other two worts. Therefore, under conditions of stress (i.e., high ethanol content), the yeast metabolism is allowed to continue due to the built up trehalose concentration. This is basically my understanding of what is going on here...

Reference: Blieck, L. et. al., Isolation and Characterization of Brewer's Yeast Variants with Improved Fermentation Performance under High-Gravity Conditions, App. and Environ. Micro., 2007, 73(3), 815-824.

Interesting, and thanks for posting that. In the course of reading about this today (when I should be working), I'm seeing more and more stuff about trehalose's role buffeting osmostress and abrupt temperature changes. It seems that trehalose not only acts as a quick energy reserve (which is of course important for dealing with environmental stress, but doesn't particularly distinguish it from glycogen), but also keeps stressed cells healthy in more specific ways.

Here's an interesting paper that explains better than I can. (It's behind the ScienceDirect paywall, but if anybody is interested it might be able to appear someplace inconspicuous on the internet.) Apparently trehalose is an anti-oxidant, which is of course useful for staying alive efficiently, also is able to protect cell organelles by mechanically bracing them in place during dehydration and freezing, and is an energy-cheap way of manipulating osmotic homeostasis.

This lab works a lot with trehalose. They claim that the only plant species that synthesize trehalose are desert resurrection plants, which also suggests that it plays a role in activity/dormancy cycles.

So why is pitching yeast into cold beer bad? Certainly doing this would convince the yeast that they're about to go dormant (as kanzimonson mentions), which is a bad idea, but where do the off-flavors that people mention come from? Is it perhaps some kind of threshold phenomena, where yeast will make (good) trehalose in response to being stuck in the fridge (big drop to 35F, but over a few hours), but (bad) protein when pitched into wort (smaller drop, but instantaneous)?