Yeast pitching for consistent results

[Tom Archer]

As I read up, research and experiment (but still as a rank newbie..) I find the subject of yeast to be the most challenging and intriguing of all the facets of brewing.

I'm somewhat averse to simply buying in packages of yeast, partly due to the cost and partly because it feels like a bit of a cop out, but I can readily see why some people find yeast management a complexity too far.

Different books have different ideas as do the various YouTube videos, but my overall impression is that whilst under-pitching yeast can easily throw up issues of consistency between batches, over-pitching, in moderation, is less critical. The imperative seems to be sufficient yeast more than a precise count - but maybe I'm missing something. My interest incidentally, only concerns British ales of moderate gravities - I'll leave exotic lagers and extra high strength beers for others to enjoy.

I noted on one video made in a commercial brewery, the use of a hemocytometer to accurately count the density of live yeast cells in yeast saved from previous brews, which gave an impressively accurate computation. However it occurred to me that unless that brewer was making batches at equal intervals, he would sometimes be pitching yeast that was young and fresh and at others pitching cells that might be alive, but geriatric, giving great variance of vitality.

The alternate route of bulking up yeast from slants or other small quantities of saved stock seems to offer greater certainty of pitching yeast that is consistently ready for the get-go, but from a practical standpoint needs a methodology that is neither too time consuming nor demanding that one gets up in the middle of the night to advance to the next stage.

One question I'm really not clear about is whether it is better to keep yeast multiplying in their exponential phase and bulk up as rapidly as possible, or do a series of bulking stages that sees the yeast plateau - or near plateau - before moving on to the next stage. Logic suggests that the yeast count might be more consistent with the second approach.

The other question I have is what impact mechanical aeration can have to increase cell count. I note that professional yeast producers saturate their propagation wort with oxygen to keep the yeast making new yeast and not alcohol. I am not considering lugging cylinders of oxygen around, but can see a simple and inexpensive way to ventilate the starter wort with filtered air from an aquarium pump - however the only video I can find of that being done does not reveal whether it makes enough difference to be worth the trouble.

 

[Alan_Reginato]

If you want to start a small brewery or play a simulation in your house, that's an interesting subject to learn and focus.

Otherwise, just do a starter for the first batch, or don't, and save the slurry for the next one. As long it's taste good, is good to go.

 

[Cheshire Cat]

So easy open the packet and sprinkle on top of the wort, simple.

 

[grooves]

I like to build a starter for liquid yeasts - it's simple enough, but you have plan ahead. It's good for two reasons - yeast viability - make sure you have enough cells and yeast vitality - the yeast cells are already fired up and consuming sugars when you pitch to your wort.

I built my own stir plate based on a computer fan with a couple of magnets glued on. There are plenty of examples on the web. But like other areas of the hobby it's easy to get carried away - I've now got my own frozen yeast bank and a lab quality microscope...

 

[foxy]

If you are making a starter there are two simple ways to aerate, shaking every so often, or a stir plate. I have put a post up before, I think it came under the name, The Travelling Brewer, I can't find it but aerating the starter and getting the yeast multiplying saves having to oxygenate the wort. I have a vague recollection that it took 3 days on the stir plate. I will have another look. Meanwhile here is some other info.
https://pubmed.ncbi.nlm.nih.gov/19175415/

 

[CJV8]

I think it depends on what your end goal is. Are you looking to learn more about yeast, save money, pitch the best yeast you can? If you regularly use the same strain then it's maybe worthwhile as like you say just buying and pitching fresh yeast each time is relatively expensive. However what you're paying for there is the convenience and consistency. Maintaining a yeast carries a cost, but also it's not an infinite solution as the yeast characteristics will drift each generation, so periodically you'd need to re-propagate from a baseline anyway. And as Grooves says, you HAVE to plan ahead to ensure you have sufficiently healthy yeast before you commit to a mash.

Having worked in a brewery maintaining 5 strains, 2 of which were used regularly and the other 3 less so, I can say it's a lot of work. It makes sense at commercial scale where the cost of using either dried yeast, or fresh pre-propagated wet pitches for each brew is very high, the cost and time of maintaining yeast(s) is justified. At the homebrew level, I'm not so sure.

If it helps here's the basic process that was used at that brewery:

- Fresh pitch of White Labs yeast into 20 litres of wort at 1.035 - 1.040, food grade oxygen for about 24 hours.
- Pitch 20 litre 'starter' into 100 litres of wort at 1.035 - 1.040, food grade oxygen for about 24 hours.
- Yeast count which would usually result in very healthy yeast, but a low count meaning most if not all of the 100 litres was pitched into a 6bbl brew (approx. 1000 litres).
- Crop yeast once fermentation is complete and prior to dry hopping (bottom cropping from DPVs). We always retained the freshest yeast we could, even if there were no brews planned for that yeast.
- Carry out a yeast count for a brew the day before to ensure viable yeast available.
- Crop up to 10 generations, at which point start from a fresh pitch and re-propagate.

The brewing schedule was based around yeast management, when we were due to crop, when we needed to pitch etc. But there was always the risk of yeast not being viable so brews were delayed until a fresh crop was available, or until we could propagate a new pitch.


Personally I just use fresh dried yeast at home for now, I do plan to get sorted with a stir plate etc to be able to make starters, but I've no plans to head down the route of a microscope, dedicated yeast fridge etc.

 

[Sadfield]

I feel it becomes a question of whether you want to deep dive into yeast management as an interesting, intellectual endeavour, as excellent results can be achieved via all the methods, be it dry, wet, freshly cropped.

 

[Northern_Brewer]

it occurred to me that unless that brewer was making batches at equal intervals, he would sometimes be pitching yeast that was young and fresh and at others pitching cells that might be alive, but geriatric, giving great variance of vitality.

In reality that's not much of an issue, as breweries typically brew on a regular (eg weekly) schedule, so it's a reasonable assumption that the yeast is in a similar state each time. The big difference in vitality is within a few days, it's less of an issue between say 1 week and 2 weeks.

One question I'm really not clear about is whether it is better to keep yeast multiplying in their exponential phase and bulk up as rapidly as possible, or do a series of bulking stages that sees the yeast plateau - or near plateau - before moving on to the next stage. Logic suggests that the yeast count might be more consistent with the second approach.

General rule of thumb is not to step up by more than 10x the volume. It's not absolute, it's fine if you sometimes need to go 20x, but it's a good general guide.

My interest incidentally, only concerns British ales of moderate gravities...

The other question I have is what impact mechanical aeration can have to increase cell count. I note that professional yeast producers saturate their propagation wort with oxygen to keep the yeast making new yeast and not alcohol. I am not considering lugging cylinders of oxygen around, but can see a simple and inexpensive way to ventilate the starter wort with filtered air from an aquarium pump - however the only video I can find of that being done does not reveal whether it makes enough difference to be worth the trouble.

If traditional British brewing is your main interest, then I would gently suggest that you look towards practices in traditional British breweries - where you won't find many oxygen cylinders, at most you'll find eg wort being sprayed by fishtails.

It's complicated, but I think one thing you have to realise is that things are different at homebrew scale. We have some disadvantages, we do have some big advantages and one is that at our scale the ratio of volume:surface area (and hence potential area for oxygen exchange with the atmosphere is much greater than a commercial brewer fermenting several tonnes of wort in a tall, thin conical. It's also easier for us to splash and shake our wort. So although oxygenation is something that's a bit of an obsession for commercial brewers it's perhaps less critical for homebrewers, particularly at lower gravities. Spraying the wort into the fermenter can get you up to 4ppm (not really enough), shaking, stirring with a paint stirrer or whisk, or 5 minutes of an aquarium stone with air can get you up to 8ppm (enough for a lot of strains), an aquarium stone with a minute of O2 can get over 20ppm (more than enough for almost anything). This is a good summary of the options : Aerating Wort Techniques - Brew Your Own

However it's worth noting that strain vary in their oxygen demands - commercial yeast labs have tended to favour the ones that need less oxygen as they suit modern brewing kit (conicals) with bottom-cropping better than traditional top-cropped shallow open fermenters. There are some exceptions - for instance WLP037 Yorkshire Square seems to get quite stressed and clovey unless you are generous with aeration - the saison family (which includes most of the strains used in Yorkshire squares - or is it that Yorkshire squares are a technological "fix" for oxygen-hungry yeast?) generally need more than most. But the "old favourite" yeast of homebrewing tend not to be super-fussy about it, and 8ppm is generally enough for most ale strains.

It's also worth remembering *why* yeast need oxygen - they're not like us, they don't need it to "breathe". They are only using oxygen to make oxygen-containing compounds called sterols which are an essential part of the cell wall and so are needed to make more yeast. Dry yeast manufacturers grow their yeast with lots of oxygen to stuff them full of so much sterols that they have pretty much enough for the 3-4 divisions they will typically make during a fermentation - which means you don't need to worry about oxygenation when using dry yeast. Another hack is to provide them with sterol precursors in the form of certain fatty acids, such as you find in olive oil. You need tiny amounts, less than a drop at homebrew scale - a common way to do it is to dip the tip of a sterilised cocktail stick in the oil and then in the wort. See this for background :
https://www.beeradvocate.com/articl...-brewers-have-tried-adding-olive-oil-to-beer/

 

[Tom Archer]

But like other areas of the hobby it's easy to get carried away - I've now got my own frozen yeast bank and a lab quality microscope...

Indeed - hardly a day goes by without me buying bits and pieces!

Maintaining a yeast carries a cost, but also it's not an infinite solution as the yeast characteristics will drift each generation

This is an area of interest. Whether it is better to accept this drift as the yeast adjusts and optimises to your wort and water minerals, or to re-enslave the original strain.

Brewers of old cropped and reused their own yeast for generations, yeast that was happy and content in the conditions provided, but putting yeast to work in conditions that are slightly sub-optimal for the strain seems popular with craft brewers, even though it requires them to regularly retrench to original stock.

 

[Northern_Brewer]

Brewers of old cropped and reused their own yeast for generations, yeast that was happy and content in the conditions provided, but putting yeast to work in conditions that are slightly sub-optimal for the strain seems popular with craft brewers, even though it requires them to regularly retrench to original stock.

Not just "of old" - the likes of Lees are up to 5000 repitches.
Some of it is that traditional multistrains are rather more resilient to repitching than single strains from yeast labs, also top-cropping means you're taking much healthier yeast than bottom-cropping from a conical.

 

[Tom Archer]

Some of it is that traditional multistrains are rather more resilient to repitching than single strains from yeast labs

One of the things I'm experimenting with is the covert recovery of yeast taken from the dregs of empty ale casks.

Cultivating such a sample on an agar plate can yield nice clean little colonies, but I realise that bulking up from a single colony is not likely to create a good sample of the brewer's yeast.

 

[Northern_Brewer]

IME the problem with empty casks is that there's often other things growing in them by the time you get to them.

Bulking up from a single colony is how the yeast labs do it, and a lot of the family brewers only have 2-3 strains kicking around, although there are exceptions. You also want to beware of the likes of Marstons who use a conditioning yeast that's not the production yeast.