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Home | The Hop Bine | Yeasty ploys ...

Yeasty ploys ...

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The irascible Charlie Bamforth is back

The second installment in Charlie Bamforth's four-part series on brewing traditions that really should have been cast aside with the advent of better technology. Prepare to be educated, stimulated, and quite possibly irritated. His target this time? The once sacrosanct yeast …

It was like a scab on your knee. You simply can’t prevent yourself from picking it. That was just how I felt whilst reading The Battle for Wine and Love: Or How I Saved the World from Parkerization by Alice Feiring. Despite an early realisation that it was going to undo hours of my most disciplined mindful meditation, I just could not help myself finishing the book to fully appreciate just how opinionated, affected and judgmental a person could possibly get.

I was especially curious to know what she had to say about a couple of colleagues of mine who inhabit the department of Viticulture and Oenology at UC Davis. I had ascertained from a cursory flip through the tome in the bookstore that they featured big time. At least one of them got a reasonably charitable review by this apparently venomous creature, though she could not help but pooh-pooh his opinions when it comes to wine technology. (Of course we should always accept the pontificating of a journalist over the experienced deliberations of a technologist – shouldn’t we?). 

To précis the Feiring philosophy: the only decent wines are made by going back to primitive approaches. And thus does she sneer about (to her mind) new-fangled ideas like adding yeast.

Now it is my experience that there is many a winemaker (perhaps the vast majority) that pay far less attention to yeast as a variable than they do the grape varietal. I well recall a visit to the world’s largest winery and asking at the appropriate point what strain they used. My guide paused a moment, scratched something and replied “hmm, not sure at the moment, I think we may have changed it recently. It’s dry, I know that.”

But to question the concept of pitching yeast into a wine fermentation, as this transparently lovelorn (quelle surprise) dame from New York seems to do as some spurious threat to the essence of great oenology, is surely bizarre? 

Rather than eschew the addition of the world’s favourite fungus, is there not a transparent opportunity here for the winemaker to achieve greater predictability and control in his or her ferments? Or is that the rub: consistency and concepts of vintage (and the attendant opportunity to bulls**t) are not easy bedfellows. 

And so many a winemaker is content with sticking fermentations: how primitive is it in the year 2012 to fail to understand why a fermentation is not reaching its end-point with the ready excuse that the skill is in the blending?

And so to beer 

But enough of this wine talk. To beer - and to the role of yeast therein. Straightaway, of course, we have to accept that there could not be a brewing equivalent of a Feiring, for the simple reason that, unlike the grape, grain is not home to Saccharomyces. The nearest we get in brewing to this wonderland of spontaneous fermentation is of course the lambic brewery, with its coolships, open roofs, passing aerial traffic of the avian variety and attendant deposits of nitrogen and who-knows-what-else to help ensure the development of that astounding diversity of micro flora (we made our own recent contribution to unravelling this complexity in the article Brewhouse-Resident Microbiota Are Responsible for Multi-Stage Fermentation of American Coolship Ale).

Back in the dawn of agrarian society (otherwise known as how beer gave us a static life style) there was of course no understanding of yeast. It seems that all those thousands of years ago the brew was seeded by organisms inhabiting added fruit – dates for instance. Worth a re-visit perhaps for those who are not to be diverted from their insatiable search for new (or newly re-discovered) brew concepts.  Sensibly, for most of us we will continue to go to our lyophilized stocks, our refrigerators, our propagation vessels in search of the strains that we know and trust.

The yeast strain: is it really that important? 

The question becomes: just how important is the yeast strain anyway? It is well known that I rather delight in teasing my colleagues who specialize on brewing yeast - amongst whom are my dearest friends – with the only slightly tongue-in-cheek viewpoint that all brewing strains are much of a muchness. 

Straightaway I will identify an exception to the rule, which of course is the ale strain used to ferment hefeweissen. There are, of course, three indicators of an authentic hefeweissen: an aroma of bananas, the whiff of clove and strictly no slice of lemon in the glass (to quote Jay Prahl of the Sudwerk Brewery, Davis: “NFL, which does not stand for National Football League”). The yeast of course is an irrelevance vis a vis the repugnant citrus adornment, but that is not the case for the first two markers.  And so try as you might with any other ale yeast or, indeed, lager yeast, you will not get the clove aroma that is due to 4-vinylguiaicol. And if you do get it in a non-hefeweissen brew then this says: ”wild yeast.” 

The hefe yeast is not alone, of course, in making the banana aroma, which is provided by isoamyl acetate. Indeed, here is my suggestion if you want to get a nose full of this attribute: go to a typical Californian Oktoberfest, sample a few of the septuplet IPA’s (or wherever dry hopping has so far got them) and then head to the bar for a well-known North American lager. The banana is manifest.  

A celebrated member of the craft beer movement hit the nail on the head.  It was a few years ago that I took a party of visiting brewers and brewing scientists to his establishment. Amongst them were the pre-eminent names of brewing yeast science – the Usain Bolts and Michael Phelps of the Saccharomyces beat. Our host welcomed the party to his little brewery (quote) and said “you know, the quality and character of our beer is largely dependent on the malt and the hops. I’m not convinced that the yeast strain has much of a role to play, other than making alcohol. In fact, when I first started the brewery I used to use yeast from the local bakery”. The wide-open mouths of my yeasty boys and girls were a treat.

Now I rather suspect that the venerable brewer was joshing. However I am equally convinced that he spoke a lot of truth as it applies to a great many beers. You will never convince me that yeast strain has a role to play in influencing the flavour of a Black IPA. The simple reality is that the blander the beer, the more the yeast brings to the organoleptic table.

However, consider again the example of the subtly nuanced lager of which I spoke earlier. It is a most refreshing product – and highly drinkable for the very reason that it does not bombard the senses. And surely that says all that needs to be said about the flavour impact of yeast? Here is a beer with a deliberately light malt character and sensibly no hop aroma or bitterness, leaving a blank-ish canvas on which yeast could stamp its presence. And what do you find? Banana. And even then, many a drinker would not notice that unless they carry out the IPA pre-load that I talked about earlier. 

Yeast and DMS - I was right ...

Yeast, of course, does make a selection of flavour-active molecules, VDKs for instance. But for the most part we try to dampen the yeast’s ardour in this direction as VDKs are something we don’t want in most brews.  For the longest time I have argued the simple reality that yeast makes DMS and now there is conclusive proof of this. Yet under the circumstances of a brewery fermentation, yeast will produce amounts of DMS that are barely going to take a beer above the flavour threshold for this compound – and for most brews these will be lesser quantities than originate from the thermal breakdown of SMM (see the first article in this series, Decoction, Concoction).

Perhaps we could use DMS further to illustrate my point. The enzyme that we showed to be responsible for making the DMS in yeast was present in all the strains that we investigated (J Inst Brew, 1981, 87, 30-34). If anything there might have been more in the cells of one of the ale yeasts despite the fact that DMS is primarily associated with lagers. One thing was much more important: what we grew the cells on. If yeast was cultured on wort there was only a tenth or even a twentieth of the DMS that could be measured if the yeast was grown on a simple mix of glucose and salts. Sure, the yeast provided the necessary enzyme, but it was the conditions in which the beast finds itself that seem to have much more importance than the yeast strain per se.

Much has been written about strain to strain differences for all sorts of yeast traits. There is considerable genetic variance between ale (Saccharomyces cerevisiae) and lager strains (Saccharomyces pastorianus – the last four letters of which will remind you that it is bottom fermenting). Lager yeast has a 50% more complex genome.  

Very few strains with a unique gene

I would contend, however, that there are no overwhelmingly dramatic differences between the strains in both categories and there are very few strains that have a unique gene (and therefore enzyme) complement – think the hefe ale yeast for an isolated example. Sure it is written that some strains have a lot more capability than others in producing higher alcohols and esters – but I suggest that a much bigger effect in most flavour instances is the impact of the wort and the fermentation conditions (fermenter configuration, pitching rate, oxygen addition, temperature, wort clarity).

Before my yeasty friends desert me, I do understand the reasons why most brewers like to stick to a tried and trusted strain. They understand its robustness, its flocculation nature, its tendency to degenerate, its quirkiness. 

My simple thesis, however, is that there is many a beer whose quality characteristics have little to do with a specific yeast strain – such as those products of pronounced roast and/or hoppy character. More so: I believe that even for the blander beers, it is the process conditions that are at least as important as the yeast strain. If I was a brewer (and many folks are eternally grateful that I am not) I would spend rather more time worrying about my wort quality, measuring my yeast count with a trusty Aber biomass probe, tweaking my oxygen levels and, of course, worrying about the health and vigour of my yeast than believing that there is something inherently magical about a particular strain (with the above caveats). 

No fear (or is that “fearing”?)

Charlie Bamforth is the Anheuser-Busch endowed professor of malting & brewing science at the University of California, Davis. 

Comments regarding this feature are welcome via e-mail to editor Tara Craig:

Coming up in November – Maturation, too much of a good thing?


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