Do I Need to Aerate if Pitching on to Yeast Cake?

[alcibiades]

The yeast only need oxygen in the reproduction phase, so that they can fully ferment the sugar into alcohol in the alcohol production phase.

...so....

is it necessary to aerate if we pitch on top of a previous yeast cake, which as I understand, has more than enough yeast for anaerobic respiration/alcohol production?

It might be important to note that during aerobic respiration, the yeast are more likely to release by-product and off-flavors, so it might not even be desirable to aerate in a yeast cake situation.

talk amongst yourselves...

 

[mb2696]

in some styles, the by-products of yeast growth are necessary to get certain flavors. if you are brewing one of those styles, i would say you certainly should

 

[Bob]

Generally speaking, it is not necessary to aerate when you knock out onto a yeast cake.

Aeration/oxygenation is necessary to provide nutrients required for cell-wall production during the growth phase. As the growth phase is more often than not skipped when you knock out onto a yeast cake, you needn't go through that step. The colony won't really go into the reproductive phase.

That said, I never recommend the practice of knocking out onto a yeast cake. The proper brewing technique is to pitch the appropriate amount of yeast for the beer you've brewed. 99% of the time knocking out onto a cake is an inappropriate amount of yeast (far, far too much). Besides, a responsible brewer should pay attention to cleanliness; that fermenter should be cleaned.

Yes, it is easy. No, it is not good practice.

Have fun!

Bob

 

[gxm]

For another point of view, I always give the fermenter my normal swirling method even when pitching onto a yeast cake, and it seems to work fine.

As to pitching too much, it really depends on what you're pitching onto the cake. If it's a huge Barleywine or a big lager, it may not be too much. I've not had any off flavors from pitching to yeast cakes, though I don't do it for styles that get their flavors from the growth phase, such as most Belgians and Hefes.

As for cleanliness, if you rack beer #1 off, than rack #2 on the cake, what is unsanitary?

To each their own

 

[Bob]

As to pitching too much, it really depends on what you're pitching onto the cake. If it's a huge Barleywine or a big lager, it may not be too much.

Even then, it always is overpitching. To properly pitch five gallons of barleywine at OG 1100, you need approximately 175ml of harvested slurry. I suspect if you measured the slurry in your fermenter, you'd find thrice or greater that amount in the vessel. I know I would.

I've not had any off flavors from pitching to yeast cakes, though I don't do it for styles that get their flavors from the growth phase, such as most Belgians and Hefes.

Most of the time you won't get off flavors from overpitching. At the most, you'll get no yeast flavor at all - which, as you point out, is a flaw in beer styles which requires esters to make it stylistically compatible. Note that English ales require esters just as much as Belgian styles.

As for cleanliness, if you rack beer #1 off, than rack #2 on the cake, what is unsanitary?

Are you serious? Have you looked in a used fermenter? It's dirty, my dear fellow. Just because good beer just came out of it is no guarantee that there's no chance the filth won't adversely affect your new wort.

Regards,

Bob

 

[schweaty]

And lets not forget about all the break material and dead yeast cells that are still in the yeast cake. I don't think Bob was saying it won't work, just that he doesn't recommend doing it.

 

[wildwest450]

Listen up people, Bob knows his stuff. Bob rules.
That is if your the same Bob as the old Bobqnx32d or something like that.

 

[Bob]

I don't know about "rules", my new signature notwithstanding. I flatter myself I have some small experience to bring to bear in matters such as these.

Yes, I am that Bob.

Regards,

Bob

 

[wildwest450]

I don't know about "rules", my new signature notwithstanding. I flatter myself I have some small experience to bring to bear in matters such as these.

Yes, I am that Bob.

Regards,

Bob

I knew I recognized that snarky tone.

 

[Bob]

Snarky!? I am the un-snarking-est bloke who ever drew breath!



Er.


Okay, so I snark sometimes. I mean well.

Seriously, there are some things I want to remove from the brewing lexicon with a flamethrower. This business of knocking out onto a yeast cake is at the top of the list. It's breaks about seventeen different "rules" of good brewing practice, it's lazy, and it guarantees only two things: An hour of saved time and mediocre beer.

Me, I'd rather take the time and effort to make my beer the best it can possibly be. Others disagree. They're entitled to their opinions just as I'm entitled to mine.

Cheers, and thanks for the props!

Bob

 

[schweaty]

Your location and the website link in your signature gave it away

 

[wildwest450]

Me, I'd rather take the time and effort to make my beer the best it can possibly be. Others disagree. They're entitled to their opinions just as I'm entitled to mine.

Cheers, and thanks for the props!

Bob

Amen. I totally agree. I will never take shortcuts and sacrifice the quality of my beer to save a few minutes.

 

[Bob]

Your location and the website link in your signature gave it away

Curses! Foiled again!



By the by, my greyhounds act like crack addicts over your dog biscuit recipe. It's really rather distressing to watch; they jump on each others' heads without regard for personal safety.

 

[jessup]

what about saving *some* of the yeast cake at the bottom of the fermenter in a sterilized container? instead of doing the yeast washing, could you save some of the yeast, trub, break material and all, then add some of that slurry to a later batch at the appropriate pitching rate? based on what you said, overpitching on a whole yeast cake is not optimal and saving some yeast & trub in a second sterilized container will give you an opportunity to clean and sterilize your carboy/fermenter. this sounds like it will work fine and i have done this in the past and it worked fine and dandy.

anything i should be worried about? precautions i should take? qualms on why this is not appropriate? what harm can a tiny bit of trub and break material do anyway?

 

[Bensiff]

Yes you want to dose with a little oxygen. Even a light lager benefits from some yeast growth. Like Bob said, tossing onto a yeast cake is bad brewing practice as it is way too much yeast which also ******* growth of new yeast.

I view trub as unwanted waste, beer crap. Why would I want to toss in beer crap to a wort that took five hours to make. May as well spend a little time rinsing the yeast to try and clean it up some otherwise its like changing diapers without wiping the baby's butt, it might look clean but it still smells funny.

 

[Yankeehillbrewer]

what about saving *some* of the yeast cake at the bottom of the fermenter in a sterilized container? instead of doing the yeast washing, could you save some of the yeast, trub, break material and all, then add some of that slurry to a later batch at the appropriate pitching rate? based on what you said, overpitching on a whole yeast cake is not optimal and saving some yeast & trub in a second sterilized container will give you an opportunity to clean and sterilize your carboy/fermenter. this sounds like it will work fine and i have done this in the past and it worked fine and dandy.

anything i should be worried about? precautions i should take? qualms on why this is not appropriate? what harm can a tiny bit of trub and break material do anyway?

I've been doing this as well, I hold back about a quart of the Cake and give the primary a good scrub, then spray it down with an Iodophor solution. So far I have had good results, but I think I may still be overpitching. If I go by Ray Daniels numbers in Designing great beers i come up with over a Trillion yeast cells in 1qt of yeast cake. His charts says there are 1.5 billion yeast cells per ML of yeast slurry, and there are 946Ml in a quart. That comes out to 1.4 Trillion cells in a quart. Does that sound right?

Also, what really defines slurry? Yeast cake with all the trub, or washed yeast?

 

[gxm]

It's breaks about seventeen different "rules" of good brewing practice, it's lazy, and it guarantees only two things: An hour of saved time and mediocre beer.

Ah, yes, *that* Bob. We've had this discussion before. I agree to disagree, despite your disparaging remarks about beer you've never tried.

 

[schweaty]

You might as well rinse the yeast to seperate as much trub from the yeast as you can. Yeah, it's a pain in the butt I'll agree with you there. But you invest so many hours into brewing your beer what is another hour or so?

 

[Bob]

what about saving *some* of the yeast cake at the bottom of the fermenter in a sterilized container? instead of doing the yeast washing, could you save some of the yeast, trub, break material and all, then add some of that slurry to a later batch at the appropriate pitching rate? based on what you said, overpitching on a whole yeast cake is not optimal and saving some yeast & trub in a second sterilized container will give you an opportunity to clean and sterilize your carboy/fermenter. this sounds like it will work fine and i have done this in the past and it worked fine and dandy.

anything i should be worried about? precautions i should take? qualms on why this is not appropriate? what harm can a tiny bit of trub and break material do anyway?

Yeast harvesting is conducted in precisely this manner daily in breweries and brewpubs all across the globe.

Yes, it's possible.

Take normal cleanliness and sanitation precautions. Make sure the implements you use to harvest and store your slurry are scrupulously clean and completely sanitized. I always use steel implements to harvest (using caution not to ding the walls of the plastic vessel) and store in glass (Mason jars).

Refrigerate your harvested slurry immediately upon harvesting.

LABEL THE SLURRY JAR.

Learn what's good slurry and what isn't. Good yeast comes from the middle layers - the gunk in the bottom of the vessel is stratified - and smells/tastes like yummy beer yeast. Don't be afraid to taste it.

LABEL THE SLURRY JAR.

Don't be afraid to just mix up the whole damn mess and harvest it. That will ensure the yeast is stored under a layer of beer - the best possible situation - in the storage vessel. If you do that, make sure you set the bottom indicator in the Mr Malty Calculator to max (25%).

LABEL THE SLURRY JAR.

If you're going to store the slurry longer than a week or so, start following the yeast-washing steps for long-term storage. It won't hurt to wash your harvested yeast anyway, though it's not strictly necessary; if you're interested in the practice, why not try it?

Oh, and LABEL THE SLURRY JAR.

If I go by Ray Daniels numbers in Designing great beers i come up with over a Trillion yeast cells in 1qt of yeast cake. His charts says there are 1.5 billion yeast cells per ML of yeast slurry, and there are 946Ml in a quart. That comes out to 1.4 Trillion cells in a quart. Does that sound right?

Yes and no. Different strains have different cell sizes. Weight and volume are only a rules of thumb, not hard and fast. 1 ml of 1076 might have 12 billion cells in it. 1 ml of 2007 might have 8 billion. Moreover, the density of the slurry has a lot to do with it. A thin, runny slurry is going to have fewer cells than a dense slurry.

Daniels's numbers are pretty much on. It's close enough to work well. The only way you're going to get more accurate than that is if you conduct your own viability tests in your own lab.

Also, what really defines slurry? Yeast cake with all the trub, or washed yeast?

Yes. Washed yeast is still not the same thing as cultured yeast straight from the smack-pack, so the same rules apply. Washed yeast is a certain amount more "dense" than non-washed yeast, in terms of cell count, because washed yeast has had most if not all of the non-yeast matter removed from the slurry. But there's no way to establish an across-the-board number of how much, because that changes in every brewery and every strain.

Ah, yes, *that* Bob. We've had this discussion before. I agree to disagree, despite your disparaging remarks about beer you've never tried.

We shall agree to differ, despite my sure and certain knowledge that I've tried beers brewed both ways and can spot the properly-brewed one 85% of the time. I don't mean to say you can't brew beer by just knocking out wort onto a yeast cake. I mean to say you can't consistently brew excellent beer as you can by following proper, established brewing procedures.

Cheers, all!

Bob

 

[Yankeehillbrewer]

Thanks Bob, I appreciate you taking the time to type all that out. I used the Mr.Malty calculator for the first time yesterday. Great tool, I'll definitely be referring to that on brew days from now on.

 

[alcibiades]

I actually inadvertinantly set up an experiment to test the "yeast cake question" a couple weeks ago:

I used a sterilized teaspoon spoon to transfer about 8-10 scoops of yeast slurry from a yeast cake into a clean fermenter.

Then I split a ten gallon batch of wort between the clean fermenter with the yeast spoonfuls and the original fermenter with the remaining trub in it.

I'll post the results in a month or so after I bottle and condition the beers from the two fermenters.

 

[Yankeehillbrewer]

I'm interested to hear what you find out

 

[gxm]

I'm also interested to hear your results.