Wyeast smackpack & yeast starter

[ASantiago]

"Smacking" a wyeast package doesn't actually activate anything. It's just a nutrient broth with a small amount of wort. The wort gets fermented by the yeast, which causes it to swell. It's a nice indication that the yeast is healthy, but it doesn't actually do anything to "turn on" the yeast. They're already ready to go.

Maybe I'm misunderstanding, but doesn't leaving the yeast in the included nutrient inside the packet cause a mini-reproductive cycle? If you pitch the packet yeast into the starter immediately after smacking the packet, aren't you forgoing the mini-repro cycle and therefore pitching less yeast cells than you could be?

 

[MalFet]

Similar to glycogen, trehalose is also synthesized from glucose-6-phosphate. It is thought to be associated with conditions of stress (i.e., starvation, heat shock, etc.). Therefore, it is considered to be a stress protectant rather than a food reserve. The amount of trehalose in a yeast cell can be used to measure its vitality and viability.

Reference: "Brewing" by Ian Spencer Hornsey

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?

 

[MalFet]

Maybe I'm misunderstanding, but doesn't leaving the yeast in the included nutrient inside the packet cause a mini-reproductive cycle? If you pitch the packet yeast into the starter immediately after smacking the packet, aren't you forgoing the mini-repro cycle and therefore pitching less yeast cells than you could be?

It's a pretty trivial amount of sugar. I don't know this for certain, but I suspect that the yeast does not undergo significant amounts of reproduction in order to metabolize it. It'd be like pitching yeast into a two tablespoon starter.

 

[kanzimonson]

The way I've heard it explained is anytime yeast sense a decrease in temp, they prepare to go dormant - building up and storing glycogen, and creating a protein coat to protect them while hibernating. An increase in temp just means their metabolic processes work faster.

I always take a cold smack pack from the fridge, activate it, and then immediately pour it into a room temp starter.

 

[ASantiago]

The way I've heard it explained is anytime yeast sense a decrease in temp, they prepare to go dormant - building up and storing glycogen, and creating a protein coat to protect them while hibernating. An increase in temp just means their metabolic processes work faster.

I always take a cold smack pack from the fridge, activate it, and then immediately pour it into a room temp starter.

Well, if this works then it's good news for me. I won't have to wait a couple of days to pitch into the starter, 'cause that's what I'm doing now (like, right now today).

 

[wildwest450]

I always cold pitch yeast. My lag times have decreased since i've started this practice. There's an article somewhere on a brewery that does it. Sorry so vague, but it does work.

Scientific mumbo jumbo, you could stop wasting the internet space and just listened to me a page ago.


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[MalFet]

Scientific mumbo jumbo, you could stop wasting the internet space and just listened to me a page ago.

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I've found that sacrificing a chicken to the goddess Ninkasi each morning has improved my brewing considerably

 

[wildwest450]

Sarcasm noted, but that's not a brewing technique.



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[MalFet]

Sarcasm noted, but that's not a brewing technique.

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That wasn't meant to be snarky, so apologies if it came off that way. I just mean to say that there's plenty of superstition in brewing, and it's tough to know what's what. There's plenty of stuff that I do just because it has worked well for me in the past, but I still think it's worth understanding what's happening.

 

[kanzimonson]

What temp should I perform my chicken sacrifice at?

 

[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)?