wild yeasts – part two

Wednesday, August 29, 2012

Returning to the discussion engendered by my earlier post (July 19) about so-called “wild” yeasts, I urge anyone interested to read through the illuminating comments that followed that post as a pre-amble to further discussion.

I did a consumer-friendly version of the blog post for the newspaper column this past weekend, and it brought some further comments from folks who seem to have the requisite background in fermentation sciences to have opinions solidly grounded in verifiable facts. That said, disagreements remain. Here are the comments made online:

Yakima Coug: Studies at UC-Davis of 'wild yeasts' from various wineries claiming this moniker indicate that they aren't so wild after all and seem to consist of those yeasts which the winery in question had been traditionally using in the recent past. Which to me indicates that wine still functions best in the ether of the more magical than scientific and to each there own, eh?


Ashlynkat: Yeah, Yakima Coug is right most "wild yeast" are just the regular old "inoculated" yeast that have taken residence in the winery from previous vintages. Sure, there is always a chance for slight mutation over the years but the likelihood of those having anything more than a negligible effect on the resulting wine is extremely low.

There is very little, if any Saccharomyces cerevisiae yeast strains out in the vineyard. The only truly "wild yeast" out there are the vineyard yeast like Kloeckera apiculata which can produce high levels of acetic acid and other unpleasant by products but only exist up to about 3-5% alcohol. Now if the winery doesn't use any SO2 at the crusher, some of those vineyard yeast will certainly start a fermentation but they won't finish it. Eventually the winery yeast left over from previous inoculation will kick in.

What happens when a winery relies on the "faux wild" ambient Saccharomyces cerevisiae yeast in their winery versus inoculating with a new batch each year is that the fermentation does usually start out slower as it takes time for the ambient yeast to ramp up their numbers. There are some benefits to a "slow ferment" and I think this is probably the more realistic difference we see coming from these so-called "wild ferments". Because truly "wild fermented" wines made from Klockera, Pichia, Brettanomyces, etc are rather nasty stuff.

Cornichon: If your vineyards are contiguous with the winery, as they are in most European growing regions, and if you return your lees and skins to the vineyard, as they do in most European growing regions, your vineyard absorbs not just the nutrients but the spent yeasts of fermentation.

The secret to terroir, in my opinion, has a lot to do with the tradition of "fertilizing" the vineyard with native yeasts, at least as important, IMO, as the underlying geology. "Terroir" is an all-encompassing term that includes unique local yeasts.

UC Davis, with its tradition of scientific hubris, may not agree. And I do understand that large-scale industrial wineries require a standard yeast. (After all, that's the mission of UC Davis, "Fermentation Science.") But artisanal wines benefit enormously from the uniqueness of "wild" (native) yeasts.

Ashlynkat: Cornichon, returning the lees to the vineyard is just reintroducing the same Saccharomyces cerevisiae strain you previously inoculated with that and is residing in your winery. And that is assuming that the Sac. cerevisiae survived being outcompeted in the vineyard by the Kloeckera/Hanseniaspora strains that tend to dominate on the grapes. While Saccharomyces has the advantage in the wine, out in the vineyard Kloeckera has home field advantage. But still, it is far more likely that the ambient yeast already present in the winery and on the crushing equipment is what going to actually carry out these so called "wild ferments".

I'm not saying there is no advantage to waiting on the ambient yeast in your winery to start the ferment but I think what I and Yakima Coug are trying to say is that we should be realistic about what these "wild ferments" really are.

It is a great marketing angle but the wineries that are most successful at doing these wild ferments are fermenting their wines with the same inoculated yeast strains that they previously used and has taken up residence in their winery. It's still Lallemand and Red Star labs "terroir" because the likelihood of a significant mutation, even after several years since an inoculation was last used, having more than a negligible impact on the wine is very low.

Again, not denying that some awesome wines can be produced by these "faux wild" ferments but I think the attention should be paid more to kinetics of how the fermentation actually happened with the length of time it takes for these slower ferments to kick into gear versus the jump start you get with inoculation plus nutrients. I think looking into that time frame and what happens to the wine during that lag and exponential growth phase will give us much better ideas about why the wine is awesome than trying to spin a romantic fairy tale about "terroir" coming from wild yeast.”

PG: So, what to conclude from all this? For me, the layman, I think it is most interesting to pursue the notion that slower ferments are what create the extra complexity. At least, that would be the path of yeast resistance...

14 comments:

Jason Haas said...

I agree with most of this, and have always thought that producers who do a "wild" yeast fermentation next to their cultured yeast fermentation were deluding themselves. Neil, our winemaker, calls these "feral yeast fermentations" which sounds about right to me.

But we have been careful to never use cultured yeast in our history. So we believe that we do have a unique population of yeasts here at the winery. Are some of them refugees from other wineries nearby? Quite possibly. But when we started, we were the only ones in our immediate vicinity, and I think we have as good a chance as anyone to actually have true natives. And they've worked for us every year.

PaulG said...

Thanks, Jason. You make an important point. Having visited the winery early in its history, I can see that you were quite isolated, and would have every chance of actually fermenting with a unique population of yeasts. No question that they have worked - you are making some lovely wines.

Anonymous said...

To me its more about ambient verses innoculated. When you spend good money on grapes, it makes no sense to not to spend a little more and innoculate with specific yeast. More likely than not if you let the ferment happen by itself, your going to get the most dominate aggressive yeast and probably a wine that resembels that.

PaulG said...

Anon - I think I'm going to title my next book of poetry "Ambient Verses Innoculated" – love that phrase!

Daniel Person said...

From the results of a confidential study conducted at some *big* winery in California, the yeast strain that completes a fermentation is often not the yeast strain with which a fermentation was inoculated.
Invariably, Saccharomyces spp will complete your fermentation, due to alcohol and SO2 tolerance, but if you perform a simple plating exercise on wines during fermentation lag phase, you'll more often than not find Pichia, Metschnikowia, Candida, Kloeckera and etc spp. It is fool hearted to believe that we control the life cycles of microbes. Simply put, an inoculated fermentation can be as 'wild' as any other.

Anna Marie dos Remedios said...

I agree with Jason, as the first and only winery in Oakhurst, CA, I'm pretty certain that my fermentations at Idle Hour are native, uninoculated, wild, authentic, whatever-you-want-to-call-it fermentations. I have never used a cultured yeast in my winery and see slower, lower temperature fermentations resulting in aromatic wines. I see consistency in the wines from particular vineyards year-in-and-out, consistency in aromatics/ varietal characteristics, but still enjoy vintage differences. It definitely takes a certain degree of trust to allow native fermentations, trust because there is less control. That is the joy of it for me. Its a bit of a journey.

Anna Marie dos Remedios
winemaker, Idle Hour Winery

Eric Murphy said...

Paul et all,

Thanks for this topic and discussion- fun stuff. I am playing around with a number of these aspects in the cellar- mostly with whites, and keeping varietal and vineyard distinction to the individual lots (we do a lot of co-fermentation).
I agree with most all of what has been said here- particularly in reference to the difference in fermentation kenetics, i.e. slower ferms/lower temps and more aromatics in the finished wine. We have chosen to not use SO2 at the crusher, but to be very selective about which vineyards and lots we use this way. Another fun aspect has been to take it one step further with the whites- feral ferms on the crushed skins to about 10 brix or so. Huge aromatics and mouthfeel, and of course tannins as well. These components can then be blended back in according to taste, ect. I think a lot of the nuances can be lost easily with the more heavy-handed winemaking- fining/filtering, ect.
Here is to a great harvest for 2012

Eric Murphy
Ott and Murphy Wines



Anonymous said...

Thanks to all who have written on this subject. In 2002 a close friend bought a very small old Zinfandel vinyard near Sutter Creek. The original vines had been planted in 1916, and through the years had seen various inept attempts at vineyard care. Our first wine kicked off spontaneously with a very lively fermentation, but the yeast died early and left us with a beautiful late harvest Zin which we still enjoy today. In 2004, we picked at a more correct sugar level and again the fermentation was spontaneous. The 2004 wine had a bright, intense flavor with a nose to match. We tried the same in 2005 picking at a higher sugar level. The resulting fermentation was scary to say the least. Very ugly gray matter started to form on the cap, and the smell was not good. We quickly inoculated with a standard red wine yeast we brought just-in-case, and saved the wine. Since them we have never been able to produce a spontaneous fermentation. Being home winemakers, we control what we can and watch the fermetation closely. We now use a commercial high alcohol tolerant yeast the gives us good color and a consistent, big, Amador Zin.

Man About Wine said...

I know there are thousands of winemakers, but I wonder if you have any input from well regarded winemaker David Ramey, who did his post grad. work at UC Davis on esters and writes some on yeasts.

Art said...

As a consumer/layman reading all of this, Paul, I've concluded that I will be taking "the path of yeast resistance" in anticipation of your next book of poetry.

Unknown said...

Yeast strain (S.Cerevisae or Byanus), in red wine, actually plays a somewhat minor role in final wine flavor. Blasphemy! you say? Well, actually the nutrient status of grape must (see yeast assimiliable nitrogen - YAN) as well levels of glycosylated and ammoniated compounds in a varietal have a much greater impact on final wine flavor. Beyond that, cap management,maceration time, fermenter shape, press type, oak and fruit handling all can have a much larger impact on final wine flavor than just yeast strain.

Most yeast strains are noted for their fermentation "esters" which are relatively short lived, and really become rather irrelevant after 6 mos to a year - important for Sauvginon Blanc- yes, but not so a Syrah which is in oak for 2 years.

Red wine flavor, although impacted by "yeast" substantially, is not heavily impacted by individual strains of yeast, as long as they are all strong fermenters and don't stick. The bigger ethos when it comes to "native" fermentation character, has to do with winemaking style. Broadly speaking, many native fermenting "winemakers" are non-interventionists, meaning they are not likely to adjust the nutrient status of their must, and the yeast will "Go Reductive" meaning the yeast will access their S-containing amino acid pool and liberate hydrogen sulfide. This, rotten egg smelling compound is the terror of any graduate program, and must be avoided at any cost, as H2S eventually complexes with ethanol to become a sulfide, mercaptain or thiol. (most of which smell like garlic, onions, burned rubber, and canned corn). However; one of these sulfide compounds: Dimethyl-Sulfide - smells of quince and truffle, so not all of them are bad per-se. However; one needs a substantial background in oxidation/reduction chemistry to understand the nuance of sulfide aromatics. But put a glass of any of these wines in front of a recent grad and watch their nose wrinkle as they call out "THIS WINE IS REDUCED" - take it away! It is an easy aroma to pick out.

However in recent years, winemakers have gotten so good at nailing down the nutrient status of their wine, and supplementing yeast with adequate nitrogen, wines have gotten cleaner, and become free of these "off" aromas - and by the sound of the critic today - too clean. A little "funk" is in right now, 15 years ago you would have done anything in the world to avoid a sulfide aroma in your wine, today, not so, people are searching it out, looking for reduction as it "is more complex". Is it right or wrong? Nope. But it is important to understand what is going on. Simply attributing it to "wild yeast" is just off base: chock it up to yeast nutrition.

Tim Donahue
Instructor of Enology
WWCC

PaulG said...

Tim, thank you for this excellent, informative post! As a followup, I wonder if you think that there are different kinds of "funk"? Funk from sulfides is different/not different from say, the "good" funk that biodynamic cultivation can express?

PaulG said...

More info sent to me by Tim Donahue, posted here with his permission:
"All things are poison, and nothing is without poison; only the dose permits something not to be poisonous." -Paracelsus

Rephrased for wine:

"All wines are faulty, and no wine is without fault; only the dosage of the compound will cause a wine to be faulty" - Me

Actually most biodynamic wines are a result of sulfide issues. This is quite simply because they cannot adjust the nitrogen levels in their wines like conventional winemakers.

To adjust the N status of a must, generally winemakers use di-ammonium phosphate, aka DAP. Dap is a chemically derived compound which contains 22% nitrogen. When added to a fermentation the yeast react quite rapidly and lay off producing H2S, which "cleans" up a fermentation in quick order.

Biodynamic farmers do not have the luxury of adding DAP. There are basically only 2 ways they can help their fermentations:

1. Increase the nitrogen in the grapes naturally by adding compost. As the partner in a 10 acre Organic vineyard, anecdotallly, I can attest to what 300 yards of compost can do to increase the YAN levels in your fruit. In 2011 our winery (in CO) added very little DAP to our estate fruit. However; the cost of a bag of DAP:$90 - the cost of 300 yards of compost+spreading = $10,000. You can see why conventional winemaking/grapegrowing wins in this cost/benefit analysis.

2. Add oxygen. Go to most BD wineries and you will see a host of sumps, basket presses, and/or open top fermenters. This is because yeast LOVE oxygen. They are a facultative anaerobe, meaning they can ferment anaerobically using nitrogen and amino acids to metabolize sugar to ethanol OR they can use oxygen to respire to metabolize sugar to ethanol. (they shouldn't but do anyway, chalk that up to the crabtree effect...another talk, another time)

Anyhow, I digress, In WA we have severely lacking YAN. Yeast need about 150mg/L to successfully finish a fermentation, and somewhere between 200-400mg/L of YAN to do it "Cleanly". Most of the fruit I bring into the College is Sub 100mg/L, with the average being 88mg/L. If we wanted to attempt to make a very broad conclusion, a BD winery in WA will most likely not have enough N, they can't add DAP, and therefore they will produce more sulfides. Now the mastery comes in making sure the sulfides are good - Dimethyl Sulfide, rather than bad: Methanethiol.

Other compounds, that come into play in delayed fermentation (see non inoculated) have to do with increased VA, which again, is not a bad thing, without it, red wines lack "lift", some people are more sensitive to it than others.

That being said, VA in and of itself is made up of 2 compounds, acetic acid (vinegar - savory) and its ester ethyl acetate (fingernail polish remover). Acetic acid, has little impact on a wines aroma in comparison to ethyl acetate, so lumping them together is rather foolish, but they are measured by distillation the same way in most wineries. VA is the #1 indicator for me that some sort of spoilage organism is lurking in my winery, so I use it as a quantitative tool not a qualitative tool necessarily.

SEE PART TWO BELOW

PaulG said...

PART TWO FROM TIM:
Again it is an easily measured compound which all recent graduates of any enological program will smell and a say "WOAH - the VA on that burned my nose. Where as the average wine drinker will think it has high ethanol (Ethanol has little aroma compared to ethyl acetate!). Strangely enough, critics tend to score red wines higher that have more overall VA. I learned this from a wine chemical engineering company that has mapped most major wine critics palates and rebuilds wines at the molecular level using a menagerie of filters, spinning cones and ion exchange columns to match said critics palate .So VA has an impact on wines, and with the right amount yum - with too much - ouch.

Lastly the other compound that arises during un-inoculated fermentations is acetaldethyde, which for the sake of keeping this rambling post to a minimum will be refered to as just aldehyde hence forth. Aldehyde smells like bruised apples, and is the principle aroma in Fino Sherry. It is a highly reactive compound which catalyzes a menagerie of phenolic interactions (see: wine color, aroma, flavor, and texture). It promotes color stability and enhances mouthfeel. The good news is that aldehyde is mopped up by phenolics in red wine, but really wrecks white wine. Which is why you don't see a lot of BD guys making white. That being said, aldehyde is easily mopped up by using a little SO2, and many BD growers, still - smartly- use a dash of SO2, as it is natural and organic, in their winemaking.

So there ya go. The ridiculously truncated science behind un-inoculated fermentations.

Post a Comment

Your comment is awaiting moderation and will be posted ASAP. Thanks!