Monday 13 February 2012


At least 10 trillion1 yeast cells are made, do their work and die.

This happens, every single week, in our brewery.

And we are only a very tiny brewery.

They do this, selflessly, so you have beer to drink.

Makes you think it does.

We used to use dried yeast from Fermentis. Good stuff it is too. We still use it when we want a yeast that has a different character. Fermentis yeast does the same thing every time with generally a very good consistent fermentation. There can be a little bit of snobbyness in the brewing community that suggests that a brewer is somewhat inferior for using dried yeast. I disagree, although that isn't really the point I'm trying to get to.

Cost is the main driver. A pack of dried yeast each brew gets expensive. A good clean brewery is as good a yeast production facility as you need for most purposes.

Hardknott now has its own house yeast. However, most of our yeast knowledge has been supplied by BrewLab and conversations with other brewers who are also BrewLab trained. The strong advice is that to ward off bacterial infection, that might ruin that house yeast, regular acid washing2 is required.

Mentioning this on twitter generated an interesting reponse. Many brewers I love and respect, including Eddie Gaedd, Dominic Dirscoll and the lordship himself, John Keeling, are very much against acid washing. As far as I can determine the argument goes along the lines that it does damage yeast and a good brewer shouldn't get bacteria in the yeast anyway.

Other brewers have stated, including my close neighbour and fine chap Ian at Coniston Brewing Co, that acid washing before every single pitching of the yeast is great.

The problem is that if I do get a yeast infection3 it might take a while to find out, as I have no in-house facilities to check for contamination, other than our palates. By the time I know I have a problem I would have to wait a couple of weeks for a new batch of pitchable yeast to be cultivated. I would in the interim have to choose to stop production, or continue and make infected beer. Either that or negate the advantage of the cost saving by regular micro-audits or premature routine recall. The argument goes, if done regularly the yeast get used to acid washing and it saves cost in the long run. The small reduction in viability can be compensated by upping the pitching rate.

I know of larger breweries who might only pitch-on their yeast for as  few as 6 generations before ordering a new cultivation as routine. With in house laboratories to check for problems and to re-cultivate this is not a cost issue.

I don't know what makes the most sense. Obviously many, many good brewers make very good beer with many different types of yeast management systems.

I guess the results are in the taste of the beer.

In any event, yeast is great. Go yeasty beasties!

I point out that I am by no means a yeast expert. We bow to any advice or opinions other brewers might have to chip in here.


1generally, a trillion is 1x1012 or 1,000,000,000,000

As Doulas Adams would say, mind bogglingly big. There are about the same number of stars in our galaxy and about the same number of galaxies in the universe.

I'm guessing the number of yeast cells in the world that die every day to make beer is probably the same order of magnitude as the number of stars that exist, give or take an order of magnitude or two.

2No, acid washing is not the introduction of LSD, as one wag suggested. It simply involves reducing the PH of the yeast slurry to 2.1 at a low temperature just prior to pitching the yeast into the wort. This kills 99% of bacteria and nearly no yeast.

It is done by adding controlled amounts of a food grade acid like phosphoric and measuring carefully with a calibrated PH meter as you do.

3In my brewers yeast, before the reader jumps to any lewd conclusions.


pdtnc said...

I too am no expert, but i do think that continual Acid-wash / Pitch & repeat must start to alter the character of your house yeast both in flavor production and the yeast becoming accustomed to the way you use it with the brewing kit you've got.

The beer you start out brewing may not be the same beer after many generations down the line. Indeed, your yeast may be virulent & happy but has it changed and you've become accustomed to its 'new' flavors?

I'm not sure this is a good thing, or it can at least work for and against you.

Thats what I think, dunno how right or wrong I am.

Ed said...

If the learned gentlemen you mentioned had open fermenters in an old farm building I suspect their views on acid washing would be different!

When I was managing the yeast at the unrighteous brewery I used to work for I'd start noticing bacteria in the yeast after four fermentation cycles. At this stage the beer still tasted fine. I'd acid wash and when I checked after the next fermenation I wouldn't see any bacteria. I thought it was great myself.

Mark said...

Stupid question: why do you want a house yeast? Is it purely down to the cost saving of not having to buy a new pitch for every batch? Surely you need the flexibility to be able to select a strain for every different beer you brew (even if that doesn't always apply)?

Bacteria and infection aside, isn't there a risk that a yeast will mutate in a way that's undesirable to your finished beer?

Me said...

I think Ade's comment about mutation of yeast is possibly correct, though, arguably the way you harvest will act to select the yeast that are most suited to that method of harvesting (like a form of natural selection). Here is where some flavour creep may happen, though how noticeable it would be, I don't know.

Interestingly, having a pilot plant here could work massively in your favour - use it to try recipes, and then use the yeast to pitch into the main brews.

Brewers Union Local 180 said...

We're up to 10 gens now with no acid washing. The biggest problem I've noticed is how long the yeast sits in the cooler before pitching. When you get beyond two weeks it starts to become a graveyard. Good thing Wyeast is handily nearby.

Unknown said...

To try and hoover up a few comments here; selective propagation of yeast can create a desirable house yeast all of the brewers own making. Indeed, how does Fullers, for instance, have its very own strain? of which they are quite rightly fiercely proud.

Renewing the yeast every 4-6 months could indeed be useful. I know some brewers get their house yeast where they want it to be, genetically, and then bank a sample to be re-propagated later if things go wrong. At a later date the old bank might be ditched as a new strain is cultivated in the brewery.

This, at least, is how it's been explained to me.

I know of several national award winning breweries, including CBOB winners, who have gone 2-3 years at least without re-call of banked yeast. They acid wash.

Bottom cropping of "ale" yeast and acid tolerance can be part of this cultivation process.

Mark, no stupid question there. I do not think, personally, that there is any reason why a brewery needs a house yeast. Dried yeast, or cultivated from a standard at a lab is fine by me.

A very real advantage of dried yeast is the ability to modify this aspect of flavour profile of the beer at will.

Personally, I'd like to get to the point where we have a Hardknott house yeast, with our own signature flavour, isolated and banked. We are a way off that yet.

BUL180, sometimes, I could grow to dislike you for your proximity to Wyeast. Perhaps an excuse for a trip out there. To collect yeast that is, rather than take some sort of revenge.

Owen said...

My gut is that your estimate of the number of yeast cells dying daily for beer production is off.

If your 10^13/week estimate is accurate for Hardknott, then there'd need to be 7x10^13 breweries of your size for your guess to be right.

Obviously some breweries might be 5 or 6 orders of magnitude bigger than Hardknott, but that would still leave as many orders short, which is a massive amount.

Unknown said...

Owen, perhaps you are right. I was going to say it was a similar number of yeast cells that die total on the earth each day, and thought that might be too far out in the other direction, perhaps not.

Either way, the numbers are very big.

If it helps my argument the number of yeast cells we produce each week is probably estimated on the conservative side here. Still, I'll admit, you have caught me out good and proper.

Owen said...

Not a case of catching out, it's just the number felt wrong. It might well be right, or close to it.

StringersBeer said...

I have to use dry yeast otherwise Becky's bound to insist on us plating stuff on selective media and doing viability and all kinds of mad stuff, requiring another fridge and an incubator and probably a whole heap of science toys for her to play with. This is all so far down my list of things to do that it's barely visible from here.

Unknown said...

Science toys to play with Stringers? You see, the arguments for playing with your own yeast are mounting. Go on, you know you want to.

Matthew Clark said...

Hello Dave

If your yeast is clean, there shouldn't be any need to acid wash it. If your yeast is not clean you should take a good hard look at your brewery hygiene processes.

I also think you should buy the "Yeast" book by Chris White of White Labs. There is a better book by Chris Boulton but I think that may be a bit advanced for you.

Also you need a microscope and haemocytometer. These are not luxuries these are essentials for good yeast management. With these tools you can control pitching rates and determine the viability of your yeast, vital for producing consistent beer.

Unknown said...

Matthew, thanks, we do actually have a microscope and a haemecytometer. We have a little bit of an idea how to use them, although we do need more practice I'll grant. I'm told that this is not good enough to catch bacteriological contamination early enough, however.

Matthew Clark said...

Hi Dave

No, It's not for catching Bacterial contamination. Not letting your yeast come into contact with bacteria is the best way to stop that, so it sounds like you might have a hygiene issue. From your blog post, you seem to be spending a lot of time applying a band-aid when what you really need to do is stop cutting your finger.



Unknown said...

Matthew, I think you misunderstand me. Acid washing is a prevention, not a cure. We do not do it to cure a problem we think we have, we do it because we have been advised that it is good practice for a micro-brewer to do it. Belt and braces and all that.

I climb mountains in my spare time, when I have spare time. Sometime in winter, or better still high in The Alps, which is great fun, but has increased risk. I try not to fall off, and also try not to drop gear down the crag. Some Victorian purist climbers objected to such things as lanyards in ice axes; a good climber didn't drop his ice axe. Modern climbers know much better and only the stupid ones don't have at least a wrist strap. Climbing a mountain can be done fast without a rope, and on ground where rock fall risk is high, moving fast is important. However, using a rope significantly reduces the risk of a fatal ground strike in the event of a fall.

Perhaps a parachutist doesn't need a safety net, but they do occasionally die because the chute doesn't open. If it were practical to cover an air field with a safety net then a few lives might just be saved.

Acid washing isn't that big a deal. Our first brew done with acid washing yeast has got to gravity and actually, we think it tastes quite good. The yeast crop done just prior to the acid wash has also come back clear of all contaminations.

Did we need to acid wash? Is it sensible to acid wash? Does it do more harm than good? This clearly splits opinion, but I totally agree that hygiene should always be as good as you can get it, acid washing or not.

Hope that clears it up.

Matthew Clark said...

Crikey. I did misunderstand.

Handling of yeast should be kept to a minimum. The more you mess about with it, the more likely you are to contaminate or infect it.

It's your yeast though and you can do as you please.

I only hope for the love of God that you're using imported American Craft Acid to wash those yeasty beasties. ;-)

Unknown said...

Matthew, don't worry, most of that reply was in my mind when I wrote the original piece. However, I thought it was going too far. Probably still is, but you gave me the excuse to write it. I enjoyed writing it. Thanks.

On the subject of Craft Acid, well off course. The great thing about there being billions upon billions of stars in the universe is that there is also great biodiversity out there. Not many people know this, but it is inevitable that with so many stars, some of them really have got life on the planets that orbit.

The lesser spotted crater giraffe, which resides on Kepler-415ez, like all life that has evolved on the planet, has stomach acid in the form of phosphoric acid. Because of the very different temperatures and pressures on the planet's surface, all life forms have a very different metabolism and chemistry to life on earth.

Anyway, at great expense, our secret team of astronauts, in our warp speed space craft, "milk" the crater giraffes risking life and limb in the process.

That's craft beer for you.

(Please note, we do not harm the crater giraffes when we collect their stomach acid; we take galactic animal care very seriously. Normally, a couple of bottles of Vittesse Noir keeps them happy - they also have a great sense of humour. Plus, they are incredibly good at calculus and complex numbers. And their poetry makes you weep.)

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