Wild Fermentation

All this talk about wild fermentation has really got me excited.  Here’s more about how yeast and bacteria turn grapes into wine.

The following thoughts are based on a conversation I had with Mike Moyer, Professor of Enology at the Walla Walla Community College, while taking my laboratory practical exam.

Wild fermentation with red wine is a great idea.  When a harvest comes in off the vines, there are dozens of species of yeasts, and even more bacteria that are living on the skins.  When we crush and destem the grapes, we introduce a lot of oxygen into the must (crushed up grapes), and this is primetime for microbes to start eating and reproducing.

The first species of yeasts to start eating and making more of themselves include names like Kluyveromyces, Candida, Hansenula, Kloeckera, Dekkera,  and Torulaspora.  Some of these are really good at making chemicals like nail polish remover (ethyl acetate), while others create funky, rubbery, tar, complexities that make a wine multi-dimensional and interesting, if not incredible.  Most of these species die when the wine approaches 3-7 percent alcohol, and then Saccharomyces takes over and eats all the sugar.  He’s the best at this.

Ahhh…I just poured a glass of 2008 Lemberger, and am really happy that I did.  Ok, back to fermenting.  Reds.  Wild.  Great idea if you are looking for multi-dimensional, borderline funkdified, traditional styles.

If you want  clean-cut, American/New World, polished, buffed styles of wine, then your producer has probably selected a packaged yeast.

White wine?  Different story.  Chardonnay?  Yeah, ok.  You can make a wild ferment Chardonnay, because…drum roll…malo-lactic conversion is acceptable.  This is the bacterial conversion of malic acid into lactic acid.  This process make a wine less tart while changing the aromatic profile from apples and fruit towards buttery and nuts.

Riesling? Chenin Blanc? Sauvignon Blanc?  Gewurztraminer?  Wild fermentation is more likely to promote the malolactic bacteria, and these wines will turn out too flabby for what most white wine consumers would prefer.

Both Professor Moyer and myself agreed that if we had a time-machine, we would definitely use it to go back about two hundred years and see how European aromatic white wine regions made their wine.

Here are the techniques modern white wine producers employ to prevent the ML conversion:

1)Refrigeration 2)Sulfites 3)Lysozyme (naturally present in tears, saliva, and egg whites) 4)Low pH 5)Sterile filtration 6)Velcorin

Of these, the one that would be best readily available to Loire, Alsatian, Austrian, Swiss, and Northern Italians of the Middle Ages, up through the High Renaissance until the Industrial Revolution would be 4) low pH.  Our bet is that pre-modern producers picked earlier to achieve these crisp, tart, and aromatic styles that are sought after for the glory and happiness that they bring.

To conclude, if you are looking to try a wild fermented, gutsy, steely, earthy Chenin Blanc, then bring a Coulee de Serrant over to our house and you can be a featured guest on the terroirist show.

Alternatively, try an Old World Winery Sonoma/Mendocino Sauvignon Blanc.  Complex, creamy, soy character with passionfruit, maybe the scent of the road after a short early summer downpour.  Yum…. this wine went excellently with our dinner of hot dogs on ciabatta bread.

Your Friend,

Michael the Microbiologist

Michael Penn

Wild Fermentation: O’er the winedark sea

Many hip wineries are starting to do what we in the industry call, wild fermentations.  So, what’s the deal?  Are these wines going to be more complex?  Should you pay more for them?  Isn’t this how all wines used to be made?  The short answer, maybe, no, and yes.  The longer answer:

First, lets meet the characters in this story.  If making wine were a Homeric tale, Saccharomyces cerevisiae would be Odysseus.  Saccharo (sugar) myces (yeast) cerevisiae (cerveza, beer) are the tiny, single-celled fungi that eat sugar, and make alcohol, glycerol, acetic acid, and a host of fruity aromatic chemicals called esters.

Next, lets talk about what’s going on in the wine.  Unlike beer or fruit juice, wine is never sterilized or pasteurized.  It is a living system full of molds, yeasts, bacteria, and of course chemicals made by the grapevine.  Whenever you have a source of sugar in nature, undoubtedly someone will take advantage and eat it.  When we crush up the grapes, we introduce a lot of oxygen into our system.  Now that we have oxygen, sugar, amino acids, vitamins, the time is ripe, and it is time to party.

So just who else is invited to this party?  Just as Odysseus arrived home to Ithaca with 100 suitors ready to take his place, we see the likes of Hanseniaspora uvarum, Metschnikowia pulcherrima, Acetobacter spp., Gluconobacter spp., Kluyveromyces spp., Pichia spp., Candida spp., and Torulaspora delbrueckii, Botrytis cinerea, Penicillin spp., and Aspergillus flavus.  Huh?

Those are just a selected few.  I name them to stress a point, there’s a lot of organisms living on grapes.   How did they get there?  They cling on to the legs and hairs of small insects like leafhoppers and flies, they’re floating in the air, or they protect themselves in fungal fruiting bodies and overwinter on the vines.  The first lesson in microbiology, microbes are ubiquitous, they are everywhere.

Saccharomyces begins its journey overwintering in the soil, or as an airborne spore.  As leafhoppers emerge from their wintery shells in the soil, they carry our hero up onto the leaves and berries.  When the ripe grapes are harvested, they are taken into the winery.  If they have been damaged by birds, rain, hail, or mammals, the grapes are likely to be infected by the vinegar bacteria (aceto and gluconobacter) or the molds (Apergillus, Botrytis, and Penicillin), and may be discarded.  If they have managed to hold their form, then they will make it into the crusher/destemmer.

Now here is where the story begins to unfold.  The party begins, and a young winemaker starts to fret.  Three or four days go by, and the vat of $4000 fruit is just sitting there, rotting.  Nothing, seemingly.  However, the various yeasts have already begun.  Torulaspora, Zygosaccharomyces, Kluyveromyces are at their finest hour.  The alcohol begins to rise.  At about 5 to 7 percent, their delicate cell membranes rupture,  they die.  Saccharomyces seizes the day, and begins to spread throughout the small lot.  No other organism can operate as well as he can.  By day 4 or 5, the temperature has risen, and if we were to examine a single drop of must (the fermenting wine), we would find 100 million yeast cells.

How did this happen?  Well made wine has a wonderful property of being 1)acidic (low pH) 2) High in sugar 3) High in alcohol 4)Low in oxygen.  None of the other microbes can survive these conditions, almost none that is.

All wine used to be made in this manner.  In 1866, Louis Pasteur published the book that would give birth to the study of microbes, it was entitled Etudes sur le Vin, Studies over the wine.  He was the first person to describe Saccharomyces, and show how it turned sugar into alcohol.  Ever since then, we’ve been looking at wine in a new way.  Several decades later, we learned how to isolate the spherical shaped yeast, put it into packages, and sell it to winemaker’s across the globe.  These packaged yeasts offered consistency, insurance, reliability.

Let me stress a point.  Most packaged yeasts are not GE, genetically engineered.  They have been isolated from wild yeasts from such far away places as France, Italy, and Germany, and they have been used to make clean wines for many decades.  In the past decade however, scientists ave begun to tamper with yeasts using techniques of genetic modification.  To date, they are illegal to use in the EU, and most winemakers do not use these GMOs.

So, to inoculate (add the package yeasts) or not to inoculate, that is the question.

Some of the wild organisms that start the party create chemicals like acetic acid (vinegar) which leads to ethyl acetate (nail polish remover).  Let me get to the crux.  When Robert Parker called the 1998 Napa Valley vintage the greatest ever, he set off a wave that is still circling the world.  The 1998 was one of the hottest on record.  The wines that resulted were high in flavor and low in acid, hot, voluptuous.  He liked them, and so did the people that only like the wines he likes.  They could be drunk young, they melted in the mouth.

The problem?  They had no acid, their pH was 4.0  When a wine has a pH between 3.0 and 3.5, none of the other organisms survive except Saccharomyces.  When the pH approaches 4.0, the wine becomes a cess pool.  Wild fermentation leads to spoilage, it is near impossible without spoling.

And so Odysseus arrives at his palace, and begins to slay the evil suitors one by one.   Some winemakers spend hundreds to thousands of dollars every crush to buy packaged yeasts.  They buy several different strains to add complexity to the wine.  Or they go wild.

Here’s the clincher.  A study several years ago showed that no matter if a winemaker used D-254, BM-45, Z-33, Pasteur Red, Prix de Mousse, a combination of all of those in different wines, or let it go wild, if you were to examine the surviving yeasts in all the different wines, it would be the same strain, most likely the strain that lives in the winery and always has.   Truly, our hero has come home.

When you buy a wine that is meant to be aged, (higher acids=lower pH), you support a more sustainable style of winemaking.  In my next story, I will take up unfiltered and unfined, and we will see more of the problems of high pH wine, and learn about winemaking’s dirty little secret, Velcorin.