Wild Yeast, Brett, Screwcaps  (10 Nov)

My  good email mate Murray, a viticulturalist in New Zealand and I have just had an email exchange that I found enlightening. Murray not only clarifies the misconceptions about "wild yeast " but then provides startling information about the transfer of Brett and finally, how these are impacted by closures. If it sound "techo" - its not  - Murray knows I am a technical cretin and need it explained simply.  

Murray: I'm enjoying reading about your trip to the Barossa ....................... but you've got to me (again) with the many referrals to "wild" yeast fermentations and to "Once the yeast is introduced, be it artificially or naturally, ....".

1. You also use the term "indigenous" yeasts - far more correct. In simple terms wineries have built up a fungal and bacterial population over a number of years. Whatever the dominant organism is, becomes the resident inoculum for that building. Except in very unusual circumstances the yeasts are not wild but resident. There are many yeasts in the Saccharomyces cerevisiae family (used to keep things simple, not technically correct term), many unsuitable for making wine and to make things even more complicated there are many “selections” within the winemaking group.

One of the least common yeasts brought in from the vineyard is cerevisiae – however it can and does take over from other yeasts (ref. Kloekera etc), over time, during fermentation. Unfortunately these other yeasts can add bad flavours (though some winemakers love them). Anyway, over time, the build up of the most favoured wine yeast becomes the resident yeast in the winery.

Nowadays this is most often S. bayanus the one known as 769 in Australia or Prise de mousse or EC1118 – the champagne yeast. This is a very dominant yeast and works at the lower temperatures favoured in modern white winemaking. It is also often used to re-start stuck ferments as it is also a K or killer yeast. I have been involved in research conducted in two countries (NZ, Ca.), where swabs were taken from clusters in the vineyard, from all the handling machinery and from within wineries and plated in the laboratory.

· Inoculum was very low in the vineyard and from the vineyard handling equipment (harvesters, gondolas, bins, trucks)

· Significant levels were only recorded at the winery.

· High levels of (non-vintage-time) inoculum were found from the wall, ceiling and “clean” tanks within the winery.

In all but one case the “resident” yeast was S. bayanus. The exception being a brand, spanking-new winery where the resident yeast was Assmanhausen.

2. “Artificial or Natural...?"  Though one can never be absolutely certain – to my knowledge there are as yet no “trans-genic” i.e. man-made, yeasts used in the southern hemisphere wine industry. Therefore there are no “artificial” yeasts so the second quote might be better expressed as ... “...with no additions of deliberately-selected dry yeast or slopes ... or from inoculation by yeasts resident in the winery ...”.

Incidentally, we were looking for “Brett” as the vineyard is always blamed for introducing this “wild” yeast into the pristine world of the winemaker. Unfortunately, in no case (that means NEVER for the doubters), was Brett ever plated from the field; from “sterile” wine tanks within the winery however, the inoculum was totally dominant. Another indigenous yeast – one giving those “wild” flavours.

Fussy bugger – yeah, I am, but there is too much bullshit in our industry already.

You could check the facts of this out but you won’t get any agreement from winemakers – just a range of opposing views. Few of them have thought to do the research – let alone in two countries!

Man-made yeasts – I think that Roy Thornton (Prof. of micro at CSU, Fresno) and Susan Rodriguez have done some work in this field and may have come up with a yeast that consumes malic acid in the course of fermentation. Not that this concerns anybody beyond makers of c-throughs!

 

Ric: Very interesting reading. I did a (very) little of my own research and even the Oxford agrees with you. Regarding your comments on Brett, if it doesn’t come from the field, how does it get into the winery in the first place?

Murray: Origins of Brett’ – no one knows for certain. One strange occurrence might help though.

Recently Brett’ has been plated from a WHITE wine bottled under Stelvin and the winery (in abject, white-jowled panic), plated everything from the winery, within and without (including the foreman’s dog).

They isolated Brett’ from the inside surfaces of two cartons of Stelvin caps – one partially used. They then swabbed about 100 of the caps from that opened bag, first inside and then outside – and on both these surfaces they recovered inoculum. They now surmise that the cardboard packaging was contaminated at some point (unknown), that they opened one package of caps but did not completely use it, returning the unused portion to the carton. On re-opening this bag and using it, the now contaminated caps ...............

It has been plated from swatches of cork maturing in the field, from ships’ dunnage, from inside surfaces of containers and from the cartons and cardboard of packaging – packaging not necessarily associated with wine corks. It would appear to be a pretty ubiquitous fella, and is part of the inoculum of many breweries. There too, it is not seen as a necessarily bad flavour – in the same way as the wine industry didn’t recognise it. Certainly when I was training in the late 70s it was seen as a regional flavour (Hunter “sweaty saddle” – or a contributory factor to that) and it most certainly is a contaminant of just about every wine-region in the world, part of the “forest-floor” “terroir” of Volnay.

We are still in the doubt phase about screwcaps (as you know from Alan Limmer), but if Nick Bullied can review The College Rieslings and Gewurztraminers made in the late 70s (hey, I was involved in some of those wines!) and find them clean and potable – this can only bode well for reds. It is just that two things will happen

1. The influence of the cork (which can be positive for some wines), will be removed.

2. The long term flavour changes caused/evolved by the equilibrium reaction of dissolved oxygen (DO) and SO2 will be profoundly changed.

I think it will be in this latter that the major difference will occur (IMO), as SO2 is more permeable through cork than oxygen – so there will be more SO2 remaining under the screw-cap seal at 20 years than would have been the case with cork (due to the permeability of SO2). I project that this may mean that all the DO will have balanced out but that some of the SO2 will remain (particularly if bottled with > 20/25ppm free SO2). This will certainly mean a lessening of those tarry characters of a really old Shiraz – I’ve grown used to them and like them – ah well.

When all is said and done, screw-caps are not the perfect closure – but as Churchill said of democracy – it is the worst (form of government) you can have – until you try any of the others. Zorks – plastic taint in whites anyway; plastic stoppers – plastic taint in reds and whites to the point of yuk; composite corks – dry, powdery flavours, hint of chemical; with only “Twin Tops” and similar stoppers coming anywhere near satisfactory performance. Of course, cork itself DOES work well ............. but .............. !!

The cork industry has had tens of millions of subsidies from the EU and has spent large sums itself – all too late really – screw-caps will eventually take over, even in the most hide-bound regions. The drinking public has been exposed to the cleaner-made wines of the New World and has revolted with its wallet – preferring the wines with fruit character to the “complicated” or austere wines of the Old World (read, wines, particularly whites, with a world class monopoly on H2S). Now the Old World is desperately trying to catch up from 50 years of self-congratulatory apathy.

The French are succeeding too, in making clean, modern wines (a dangerous precedent for us in the southern hemisphere). Our danger is that we will be subject to a similar attitude of self-congratulation.

The other day I opened a bottle of Tyrrell’s 1994, Vat One ... corked. If it had been bottled under Stelvin that simply would NOT have happened. I’ve drunk twenty year old Lindemans Reserve Semillons that were perfect (hot, buttered toast) and a 20 YO Rothbury Semillon (perfect, almost like a fresh young wine) – but can no longer afford the risk (nor the money), and frankly – apart from Port which they refuse to screw-cap – I shan’t bother with corked wines for the cellar, ever again. Too few years left now to bother with the f***ing about.
 

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