We know yeast plays an important role in bread and winemaking (not to mention the future of biofuels…). But how does it work in beer?

No surprise, the role of yeast plays out much same everywhere it goes. Yeast eats. Well, put more specifically, yeast metabolizes—at least, that’s what we care about. Not that we’re not happy that yeast gets a full meal out of the sugars in our grape juice, but we’re happier with what it produces—wine. The same is true for bread and beer. The yeast we put into the wort (the liquid made from boiling malted grain) likes to feast on those grain sugars, and we let it, because the byproduct of that primal gluttony is alcohol. Yes. Yeast turns our cereal into beer.

But it’s not just any kind of yeast. There are certain special kinds involved in brewing. And while you won’t have to memorize Latin nomenclature or identify your favorite beer by the yeast that fermented it, it is actually useful to know about two kinds of yeast directly related to the two major fermentation methods involved in beer production. It all comes down to ale vs. lager.

Chances are, you’ve been in a situation where a beer was interchangeably referred to as ale or lager, and hoped no one asked you the difference. (We’ve all been there.) The difference is this: how was the beer fermented? Ale is top-fermented, meaning the yeast is applied to the top of the wort, and at a higher temperature. Top-fermenting is the oldest method, and the yeast used for it is called Saccharomyces cerevisiae. Top-fermenting tends to yield more flavor, as esters (a byproduct of both kinds of fermenting) are more pronounced in warm fermenting, as are phenols (which include things like tannin).

Lager, on the other hand, is bottom-fermented, meaning the yeast works at the bottom of the wort, at a much lower temperature. And that’s because the yeast involved in bottom-fermenting are a hybrid of Saccharomyces cerevisiae and a yeast called Saccharomyces eubayanus, a wild yeast from Patagonia that probably hitched a ride to Europe on a trade ship a few centuries ago. Unlike S. cerevisiae, S. eubayanus can thrive in much colder temperatures—and their baby yeast, S. pastorianus, inherited that ability (thanks mom!).

Because the reaction takes longer, bottom-fermented lagers ferment at a low temperature for a longer time. The result is a “crisper” beer that has less of the pronounced flavors of an ale. A classic example would be a German pilsner. (Lagers are by far more popular worldwide, though ales are usually more complex.)

You might think we’ve forgotten the third essential kind of fermentation—and the yeast we have to thank for it. We didn’t. Wild fermentation is the third essential way a beer can be fermented, relying primarily on, you guessed it, wild microbes, especially Brettanomyces, a yeast known (and often sought after) for its ability to give beers a decidedly funky flavor profile. An increasing number of American craft brewers are playing with wild fermentation, although generally in as controlled a setting as that of traditionally fermented beers.

I've read about re-using the yeast at the bottom of the fermenter but am not sure exactly what this means....

After bottling the beer do you just leave what's in the bottom there and then dump your next kit on top, stir it up and that's it?

Do you need to add more yeast?

Obviously this would mean that you can't just dump hot water straight into the fermenter to mix up your kit either or you'll kill the yeast yeah?

Currently I have a Morgans Dark Ale that I added liquid choc malt and also some steeped choc grain and goldings hops and Safale yeast in there and it should be ready to bottle next weekend.

I was thinking of just pitching an amber ale on top of the trub to see what that tastes like. Or would it be better to just clean out the fermenter and start fresh since the types of beer are different?

thanks, Rich

• 2

You've got it, just dump your next (cooled) wort on top of the old yeast cake and you're in business! I often do this, first brew in primary for a week, make second wort, rack first brew to secondary then rack second wort onto the yeast cake. I usually brew a stronger and/or darker beer second.

The other option is to harvest about a cup of the slurry, rather than using the whole thing again.

• 3

Thanks MCWB.

Why do you rack the second wort onto the yeast cake? Wouldn't dumping it in and mixing it all up and oxygenating it be better for the yeast to start fermenting?

And so no need to add more yeast with the second word right?

thanks, Rich

MCWB

Well-Known Member

• 4

Actually I just syphon the cooled wort straight from my boiler, but only because I haven't been bothered putting a tap in it yet! I make sure it splashes around a bit too, so it's nicely aerated.

Correct, you don't need any more yeast. Compare how much is in your yeast pack to how much is on the bottom of your fermenter...

• 5

  "Wouldn't dumping it in and mixing it all up and oxygenating it be better for the yeast to start fermenting?"

Yes this is correct, just dump it in amd mix it all up, you want lots of oxygen at the start.

A better method is to harvest about half a cup of slurry from the bottom of the fermenter and add this to a fresh brew in a fresh fermenter. This way, you are using a nice clean fermenter and not adding truckloads of yeast. Pitching too much yeast can be a problem.

Also, with pitching large quantities of fresh yeast, watch your fermentation temperautures as they can take off.

There is no need to add extra packet yeast to the second brew if you have al;ready pitched some fresh slurry in it.

If you want, check out the White Labs webpage, //www.whitelabs.com for details on yeast care and yeast washing.

Watch out for escaping yeast, you may need to fit a blow off tube to your primary fermenter.

Jovial_Monk

Guest

• 6

Slurry (the yeast from the bottom of the fermenter) has loads of yeast cells, no need to aerate the wort you pour onto it.

Probably the best way to do it is to use more than one fermenter, and pitch the yeast cake into progressively stronger and darker beer.

Make up wort one, pitch a liquid (or other, but the cost of liquid yeast makes this repitching almost mandatory) yeast and ferment out. Just before racking beer 1 make up wort 2 in a new clean fermenter. Rack beer 1 out, leaving the tiniest bit of beer behind. Close tap, fit lid, swirl fermenter to 'liquify' the yeast cake, then run this through the tap into wort 2. Fit lid and airlock to fermenter 2 and watch the airlock start bubbling immediately

Clean fermenter 1 and have ready as fermenter '3', repeat the process with beer 2 and fermenter/wort 3 but use only half the yeast cake which will now be bigger than it was originally (in fact, you can pitch the cake from fermenter 2 into two fermenters to get 4 beers out of one liquid yeast.

Big breweries repitch yeast, usually bottom cropped, 8-10 times then the yeast is used only for making Vegemite. Home brewers should only repitch twice. It calls for a bit of planning, what beers are suitable for pitching with whatever yeast and working out in what order to brew and pitch the beers.

Jovial Monk

• 7

and thinking of cost its a great way to maximize liquid yeast usage.

cheers big d

• 8

  Jovial_Monk said:

Slurry (the yeast from the bottom of the fermenter) has loads of yeast cells, no need to aerate the wort you pour onto it.

<snipped>

Jovial Monk

Hi

Yes, the slurry has loads of yeast cells, but oxygen is important to the health of the yeast cell and you have to aerate and to allow the yeast to multiply. If you don't, the only yeast cells that can convert your wort to beer are the viable ones of the slurry.

There are loads of professional brewing references that tell you that oxygen is required.

Cheers Pedro

• 9

Thanks for all the advice. I'll probably be doing this next weekend so I'll see how it all goes

Rich

• 10

Am thinking of doing this for the first time, if you want to store the yeast/slurry can you just bottle the collections and store it in the fridge until you need it?

• 11

  sluggerdog said:

Am thinking of doing this for the first time, if you want to store the yeast/slurry can you just bottle the collections and store it in the fridge until you need it?

[post="60299"][/post]​

Slugger,

Yes, just store in bottles in the fridge & warm the day before to brew temp...

• 12

Works fine,

Just make sure you handle your yeast as cleanly as you can. Don't store it in the fridge for too long either.

I use similar methods. My beers are fermented in glass carboys. If I wish to re-use the yeast after racking what I do is flame the mouth of the carboy with a gas match after wiping it first with some metho or Iso-propyl swabs. Then I just swirl the carboy and pour the contents into a 2 litre mason jar.

These are good as they have a wide mouth and are pretty easy to sanitize.

On brew day all I do is take the yeast out of the fridge a few hours before pitching the new batch. I pour the old beer (carefully) off the top, then add about 500ml of the new wort after cooling.

I let my new brew sit in the kettle for about 30mins after cooling and whirlpooling to let the trub settle. Then I get my yeast and fresh wort and shake it around to mix the yeast into the wort (carefully). This is then just pitched to the fermenters. Truth be told if your yeast is pretty fresh you could probably to the same thing with some sterile water instead of wort.

Hope this helps -

Warren

• 13

Slugger if you intend to store the slurry under wort for more than a week or two, beware that it will continue to ferment even in the fridge. Opening a longneck of 2 month old slurry is an experience I wont be repeating, slurry all over the kitchen including the ceiling, floor, sink, bench, walls and myself, Mrs Nonic was not impressed uncovering stinky slurry in the nooks and crannies of the kitchen for the next week or so.

Edit: I was surprised at the pressure in that bottle, if it wasn't an old Pick Axe Coopers bottle I'm sure I would opened the fridge oneday, knocked it by accident and copped a face full of glass.

Forgot to add, I don't store slurry under wort in capped bottles anymore. Either store under very well boiled water as per this thread Yeast Farming by Chiller or as I have at the moment reuse the slurry from one brew to the next.

• 14

I suggest that you store yeast in the fridge in plastic bottles just in case + loosen cap from time to time to release pressure!

• 15

  nonicman said:

Slugger if you intend to store the slurry under wort for more than a week or two, beware that it will continue to ferment even in the fridge. Opening a longneck of 2 month old slurry is an experience I wont be repeating

Nonicman, Was the wort fermented right out? :blink: Was the fridge turned off? Perhaps it was just one of those things? I used to save the slurry from my worts in a sterilised vegemite jar & re-use 8 or 9 times before culturing another Coopers Pale Ale yeast for re-use. Never had any problems. Stopped doing this when I realised that splitting up & saving the original liquid yeast was a more hygenic option.

• 16

  Tidalpete said:

Nonicman, Was the wort fermented right out? :blink: Was the fridge turned off? Perhaps it was just one of those things? I used to save the slurry from my worts in a sterilised vegemite jar & re-use 8 or 9 times before culturing another Coopers Pale Ale yeast for re-use. Never had any problems. Stopped doing this when I realised that splitting up & saving the original liquid yeast was a more hygenic option.

[post="60339"][/post]​

Pure primary wort slurry, was it fully fermented out? I thought so at the time I reasoned that the fridge would stop any further fermentation anyway. This was my first attempt at storing yeasties. That 750 of slurry didn't look too apealling against the new yeast vial I had so didn't get used for the next brew, would have been fine otherwise. Soon after that I was washing the slurry as per Chiller's post and other articles then stored under sterilised water in capped stubbies. It was when I was looking through the library of yeast stubbies after a few months of gentle proding (something about an invasion and take over of the fridge, couldn't we just buy what we need each day?). Thats when I remembered the Burtons Ale yeast slurry. I guess the slurry could have been in the fridge two months it could have been more like 4.

Sorry to hijack the thread, wouldn't want anyone to get injured whilst in the pursuit of our great obsession. Even it if I look like an idiot :beer:

Shameless reposting of Yeast Farming

Cheers,

Jason

edit: spelling

• 17

There's nothing wrong in adding personal experience to the forum Jason! The first time I tried to re-use yeast slurry, I put 2.8L of it in a 3L coke bottle and thoughtfully put an airlock in a rubber stopper on top...I eventually found the bung elsewhere in the laundry the following morning - thank god it was a tiled area, and I managed to wipe down the brand new Maytag front loader before SWMBO saw it Cheers, TL

• 18

  nonicman said:

Thats when I remembered the Burtons Ale yeast slurry.

Nonicman, Musing on your misfortune overnight I got to thinking that the yeast in question may have been a lager, or similar low fermenting yeast that had not quite fermented out fully. From your previous post I see that it was an ale yeast. I had previously assumed that an ale yeast would be dormant at such low temps in the fridge. Clearly, this line of thinking is incorrect. I'm glad I don't store slurry anymore. Chiller's post on yeast farming is excellent & I am storing it away for future reference.

Wortgames

'Draught' is not a beer style - it's a lifestyle

• 19

In my experience any yeast will continue to ferment, even at low temps and under 'fermented' wort.

I think one of the things that is happening is the yeast is slowly mutating to digest the tougher sugars and dextrins in the wort, and I'm sure it will be autolyzing to a certain extent too albeit slowly.

I have stored slurry for several months in Grolsche bottles (cracking the seal once a week or so to relieve pressure). I would be happy to use yeast stored this way for about 3 months, but after this I would say that it has probably mutated enough to affect flavour and attenuation.

This is just based on observation and guesswork though, so I'd be interested to hear if anyone agrees / disagrees.

What is the difference between top fermenter and bottom fermenter?

Top-fermenting tends to yield more flavor, as esters (a byproduct of both kinds of fermenting) are more pronounced in warm fermenting, as are phenols (which include things like tannin). Lager, on the other hand, is bottom-fermented, meaning the yeast works at the bottom of the wort, at a much lower temperature.

What is the residue in the bottom of a fermenter at the completion of fermentation?

The yeast layer is known as the lees; however, as everything at the bottom of the fermentation vessel coagulates and lumps together, the lees become part of the trub. The amount of trub that accumulates at the bottom of the fermentor varies depending on style and ingredients.

What temperature is top and bottom fermentation?

Top ferments ferment at high temperatures of 60 to 75°F, while bottom beers ferment at cooler temperatures of 42 to 54°F.

Is beer top or bottom fermented?

Ales are fermented with top-fermenting yeast at warm temperatures (60˚–70˚F), and lagers are fermented with bottom-fermenting yeast at cold temperatures (35˚–50˚F). Because of their warm fermentations, ales can generally ferment and age in a relatively short period of time (3-5 weeks).