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Welcome to YeastBytes |
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| Like a five year old who has just been refused those must have black chunky shoes, here we are kicking and screaming with YeastBytes no.4. Despite the unrelenting pressure, we have stuck to our task to deliver a late summer bumper edition with some more finely honed pieces in our bimonthly homage to all things Saccharomyces. |
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| The lead article in this issue is something of a party political broadcast on behalf of the 'Yeast Supply' party, often seen as failing to punch its weight and grabbing too few votes. This piece focuses on the benefits of yeast supply or management through the eyes of a 'party worker'. Unable to resist the pun, 'freeze dying' hits home on the perils of using dried yeast from commercial collections for yeast supply. For the first time in YeastBytes' young life we take a deep breath and consider the thorny subject of the 'generation game' and the pros and cons of culling and replacing yeast. Next up Cara new boy, Pieter Swanepoel introduces ('passport control') some of the amazing developments in molecular methods that have made strain fingerprinting a quick and cost-effective monitoring tool. YeastBytes regular Chris Giles mulls over the joys of the QA of microbiological media. Finally, in the bizarre corner that is 'did you know?', YeastBytes catches up on the spread of Australian yeast extract in art! |
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the generation game |
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| I didn't appreciate that the TV game show that gives this piece its title originated in Holland as 'Een van de acht' or 'one of the eight'. The eight contestants spawned the memorable catch phrase from the venerable Bruce Forsyth, 'lets meet the eight who are going to generate'! Perhaps one of YeastBytes' more surreal links but another piece of vital information for loyal YeastByters the world over! Enjoy! |
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| Anyway back to the real world, the clues for this piece are in the title. This 'generation game' is all about the regular replacement of a yeast 'line' after so many generations. The definition of 'so many' would be a great (but rather unlikely) subject for one of those radio phone-in programmes. Just think of the sparks flying between a brewer who swears blind that 20 generations is right whereas another equally opinionated brewer insists on no more than three or four generations. Things would get really tasty, when the call came that 'we've been using the same yeast for years without any problem'.
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| Unfortunately, in a world that hungers after 'best practice' there is no definitive right or wrong in terms of 'generations'. For some it is a local, flexible, decision. In other breweries it is specified in work instructions or global policy. And to complete the spectrum there are breweries for whom introduction of a new line of yeast is a rare, infrequent 'needs must' thing. By way of example, some UK brewers claim to have last changed their yeasts 'several generations ago' - they are, of course, referring to the acts of their brewing Ancestors (Grandfathers or sometimes even Great Grandfathers) working in their family-owned breweries, rather than using the phrase in its more generally-understood form.
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| The rhymes and reasons behind controlling generation number (or not) are based on three drivers. Firstly and historically the hygiene of yeast slurries or cakes was difficult to assure, secondly concerns about the stability of the performance of a yeast line and thirdly, "we've always done it this way"! |
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| Of these, arguably 'hygiene' is nowadays less of a concern, with the availability of better, more efficient CiP and closed vessels across the yeast 'supply chain'. Further, many breweries acid wash their yeast as a routine process step but it's worth remembering that acid tolerant wild yeasts are unaffected by this treatment. As to 'stability' we enter the world of anecdote, intuition and beliefs. I've heard it said many times that "our yeast gets better/worse (delete as appropriate) with generation number". The explanation for either position could be fun to debate through YeastBytes or over a pint in some exotic location! Certainly some brewing yeasts may well adapt over time but poor propagation or pitching control may also contribute to the debate. On top of this is the issue of genetic instability. Although not the time (YeastBytes no 6 perhaps), genetic instability is real particularly, in lager yeasts, and can be observed in propagator and fermenter. Going back a step, yeast supply may also be implicated if the yeast is not pure and contaminant yeasts or strain variants are present and subsequently selected. |
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| Finally the "we've always done it this way" factor is both a strength and a weakness in modern day brewing. Whilst an admirable trait in terms of cementing the right way of doing things it can also be an obstacle to change. Whilst a naturally conservative industry, "we've always done it this way" can smother or slow innovative ways of doing things. My plea would be for this conversational block to be replaced by a evidence based insight or "we'll look at it"! |
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| So what have we got? Mindful of ensuing process complexity should Brewers critically assess their "how many generations?" rule? Are some strains being culled too early or too late? Can we move from anecdote and received wisdom to a more observation based specification? One thing though on which I'm clear, is that yeast lines do require to be periodically replaced. This demands best practice from both yeast supply and propagation activities. |
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| David Quain |
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