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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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supplying the benefits |
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| From the perspective of a job description, my role - in addition to overseeing the creation of each issue of YeastBytes - is to talk up the importance of an assured, robust yeast supply process. Sexy or what! Regrettably though, the provision of fresh yeast from the laboratory to propagator is all too often perceived as an activity that requires little attention, support or importance. This approach is at best unfortunate and, at worst, commercially damaging! Like the snowball rolling down a snow covered hill, a small oversight, poor practice or a passed-over problem at the outset of yeast supply gets bigger and bigger as the yeast becomes established in production. So is this alarmist stuff? Is it a really an issue that requires focussed attention within a Brewery, a global organisation or through outsourcing to specialists like Cara? |
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| My answer? Well, there is nothing quite like the experience of yeast supply going wrong to win over the interested or convert the disinterested! In a previous life - as briefly touched upon in YeastBytes no.3 - I had the task of unravelling a yeast supply issue that had paralysed a major brewery. Then as now, phenolic lager was not part of the NPD programme, particularly in such awesome volumes. So this was a tricky problem to resolve and, once sorted, I had the job of ensuring it would never happen again. Mmmm so no pressure then! |
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| So back to a familiar refrain .... yeast supply is important, nay critical to a well run brewery. Veteran YeastByters will know the 'lyrics' that go something like this. First store the right yeast in the bees' knees of cell storage, liquid nitrogen. As argued elsewhere (see 'the generation game') it makes sense to regularly introduce fresh lines of your brewing yeasts. So periodically (say every four months) or as required, recover your strain(s) under controlled and quality assured conditions. For tip top assurance not only do the right microbiological things to guarantee a clean yeast but validate strain identity using PCR (see 'passport control'). Having supplied/received the yeast slopes (appropriately labelled and with backwards traceability) store them securely in a fridge which, ideally, is only used for yeast supply. Use the slope within its shelf life (3-4 months) and ensure that all of the slope is sacrificed in the first step of laboratory propagation. In my experience it is helpful to minimise the risks by having a second person on hand to observe and check, particularly if more than one yeast is being processed. |
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| It is likely and best practice that only one yeast (or perhaps two if the yeast is 'mixed') will be propagated at any one time. The early steps of propagation should of course be performed to 'good laboratory practice'. Scale up steps in the laboratory should be minimised to as few as possible. Further, as a principle, each step should be 'aerobic' with the larger scale (typically) 20l vessel forcibly aerated/mixed. |
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| So to wrap up, the tenor of yeast supply is to be safe and assured. It is certainly not overkill to demand that in-house or outsourced yeast supply has gone to great lengths to remove or minimise any risks to strain identity or microbiological quality. In particular, the risks of strain mix-up should be reviewed and addressed so as to ensure that the right yeast is always supplied and subsequently propagated in the brewery. As noted at the outset, I've been there when yeast supply goes wrong. I'd prefer for you not to re-live the experience. |
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| David Quain |
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