johnr's Brewing yeast tips

Brewing yeast tips

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A hobby in its own right?

When people ask if I have any pets, I've been known to reply "Yes. Yeast!"

Looking after this little organism (technically a single-celled plant) can be both demanding and satisfying. With the right approach you'll get consistently good brews, and a worthwhile saving on the cost-per-pint.

Sedimentary yeasts

The popular way to start a fermentation is to buy a sachet of dried yeast granules from a homebrew shop, activate as directed, and add to the wort. I've tried many such yeasts, mostly with similar results: a docile but rapid fermentation, no surface crop (even from some which describe themselves as "top fermenting") and a "clean-tasting" (i.e. free from yeast character), rather dry resulting beer. Similar comments apply to my experience with a couple of "wet" samples from a well-known American supplier, with the added disbonus of a £5 hike in the cost of the brew.

Because the yeast sinks to the bottom, you can scrape up some of the sediment to start your next brew. Having syphoned off the beer, tip the bin to drain the sediment, then scoop up a few spoonfuls into a food bag. Suck the air out, seal, and store for up to 2 weeks in the coldest part of a fridge. To repitch, drain off the liquid which will have separated out from the yeast, then just spoon the remainder straight into the new wort. You can also use your surplus yeast to make good bread.

I have a theory that the high proportion of dead and decomposing cells in such recycled sediment benefits the surviving yeast. Certainly the subsequent brews get better each time. But the longest I've managed to keep a "dried" yeast going is for about 7 brews. After that it seems to lose interest in its job.

Top cropping yeasts

Once upon a time most brewing yeasts floated on the surface of the wort, forming a thick layer of creamy, seething froth. Nowadays this tendency has been bred (?) out of many strains as it's an inconvenient habit in a modern enclosed fermenter (baking yeast will give you a spectacular performance, but it's a pig to clear). However, there are still some varieties which throw up sufficient cells to let you skim them off for recycling. You'll know your yeast has a top cropping tendency if the brew looks like this towards the end of fermentation.

There are pros and cons to using a top cropping yeast. In my experience they can be recycled more times, presumably because you're collecting only proven live cells; however, a top crop is exposed to the air, and so is more susceptible to airborne infection. I've had to abandon recycled top yeasts due to sourness, whereas the terminal problem with bottom ones is more likely to be incomplete fermentation.

Unless you have a vigorous old-fashioned top cropper, you won't get nearly as much material to recycle as from a sediment. Towards the end of fermentation, when the gravity is about 5 degrees above the final value, skim and discard the crop so that a new, clean, hardy one can form. Then, when it's done so, use a teaspoon to skim some onto a piece of absorbent kitchen towel. Press another towel over this to remove most of the froth, then scrape the yeast back onto the spoon, form into a ball and squeeze again between kitchen towels. After repeating this process a few times you'll end up with fairly dry stuff that's starting to break into flakes as shown. Roll it into a ball, cover airtight with food wrap, and store in the fridge until needed for the next brew.

The amount recovered in this way can be quite small, and a tip I've picked up from the commercial world is that you should pitch as much yeast as you can - a certain head brewer was really upset by talk of a teaspoonful for a 5 gallon brew! So I always try to boost the quantity by making a starter bottle the day before brewing. Heat ¾ pt water to boiling point and stir in 4 tbsp dry malt extract (e.g. Muntons Light Spraymalt). Hold the temperature for a few minutes, cool the pan in a bowl of cold water, then pour from a height through a funnel (to aerate) into a clean pint bottle. Add the yeast, shake well, dry inside the bottle neck, wipe with sodium metabisulphite solution, then insert a cotton wool plug as shown below.

Yeast from bottled beer

With care and good hygiene practice, you can rescue the minute deposit of yeast from the bottom of a bottle-conditioned beer, and multiply it into enough to start a brew. Buy a bottle dated as far ahead as possible (a year is good) and store it upright in a cool place for a couple of days to settle and compact the sediment.

Have ready some cold starter wort prepared as above, and a pint glass. Start by thoroughly cleaning the outside of the bottle, including under the rim of the crown cap. Having removed the latter, slowly and carefully pour the beer out into the glass, leaving just the sediment behind. Then proceed exactly as for making up a starter (except that the yeast is, hopefully, already in the bottle!). Such a culture will take a few days to get going, but when you can see signs of froth forming it's time to make the brew.

Unfortunately, bottle-conditioned beer is now much less widely available than it ought to be. Also, some breweries use different strains of yeast optimised for primary fermentation and bottle conditioning, so success with this method isn't guaranteed - but it's fun to experiment. In the early 2000s I used two samples cultured from Hopback Summer Lightning. They were very well-behaved; it fermented steadily (albeit rather slowly), threw up a good crop, and responded well to isinglass finings. I kept the first sample going for 22 brews. Another success around the same time was yeast from a bottle of Ballards Nyewood Gold, which gave a really fine flavour to the brew.

Yeast from a brewery

The best yeast I've ever used came from a visit to Greene King's brewery in 1978. This single sample and its descendants supplied me with excellent beer for the next six years, 115 brews altogether! It formed a thick surface crop that readily yielded a spoonful for propagation, and left the beer transparent (thus saving the cost of finings as well as yeast).

The fridge in which I stored this yeast was unusually cold, and most times the ball of yeast went slightly below freezing point, which didn't seem to bother it (freezing has been known to kill lesser specimens). I always made a starter bottle the day before brewing.

During those "GK years" I learned the importance of collecting only the final crop for propagation. It's tempting to skim when the crop is at its thickest (gravity about 1015-1020), but our little friends soon realise their ancestors enjoyed the easy, high-gravity life, so why should they work any harder? In real terms, you find that successive brews get more and more reluctant to ferment out to dryness. By keeping careful records (see below) I was able to spot this trend, and watch it go into reverse as I applied a new regime of collecting only the final crop at around 1010 gravity.

I believe I'd still be using that yeast had I not moved house in 1984 and neglected brewing for too many weeks - the yeast simply got bored in its fridge and died. I was delighted to be given a new sample during another brewery visit in 1990, but that one didn't seem to be very happy in my set-up, surviving only for a few brews.

The importance of record-keeping

The only sure way to organise your brewing and maintain consistency is to keep a log sheet.

Over the years I've whittled down the paperwork to a single line per brew. The entries record the times of all the key events of the day, plus temperatures and quantities of ingredients. Hopefully the headings are self-explanatory; the 3 mash temperatures are measured (when I remember!) before and after pitching and at the endpoint. From records like these I can predict the best strike temperature, guess when it'll be reached, and spot trends that might warn of changes in such things as the boiler thermostat and the yeast performance. For example, the racking gravity is rather high in the last line above, but that's probably explained by the seasonal drop in temperature.