Wine Yeasts: The truth about spontanious fermentations

This article was taken from Science Alert

Tuesday, 05 August 2008

University of Auckland Wine is the result of a competition between microbes for nutrients, research suggests. Scientists at The University of Auckland studying yeast used in winemaking have discovered the reactions that turn grape juice into wine are a mechanism to ensure the yeast secures many of the nutrients from the fruit. The results are published in leading international journal Ecology, and one of West Auckland’s wineries, Kumeu River, is pictured on the front cover. The researchers studied the microbes present on grapes from the field to the cellar at Kumeu River Winery, and discovered very low levels of Saccharomyces cerevisiae, the yeast required to convert sugar to alcohol, naturally present. However, it created a warm, high alcohol - low oxygen environment which is toxic to all other yeasts and microbes during the fermentation process allowing its numbers to rapidly increase. This environmental-engineering is wasteful for the yeast, as it is more efficient to completely metabolise the fruit sugar to water and carbon dioxide, but the fermentation releases ethanol and heat and ensures S. cerevisiae is the sole survivor.

"Environmental engineering is a known concept, originally described by Darwin," says Dr Mat Goddard of the School of Biological Sciences. "However, while many organisms modify their environment - think of beavers building dams - the evolutionary effect of this has never been measured before. In the case of winemaking, it seems Natural Selection has caused yeast to adapt to change its environment to create a competitive advantage over other microbes in the niche. We first have to understand the fundamental process of winemaking if we are to ever reliably apply the results so the NZ wine industry can benefit."

The research was part funded by a six year Foundation for Research Science and Technology project, looking at the specific characteristics of New Zealand Sauvignon Blanc, and the rest was funded by the School of Biological Sciences. The FRST project, headed by The University of Auckland and in collaboration with New Zealand Winegrowers, HortResearch, Lincoln University and winemakers nation-wide, is looking at the effects of growing conditions, fermentation and aging in the bottle on wine aroma. 

This post is in response to the post that was written by Arthur over at Wine Sooth. I am continually amazed at the level of misunderstanding that dominates the wine industry today. People can make science say whatever they want and I believe that Arthur is doing just this with a majority of his posts. S. cerevisiae does not have to be present in large numbers to overtake the fermentation. One of the major reasons fermentation's today have a problem finishing is because of the high brix content. Inoculations with laboratory made yeasts have not been successful for centuries because they have not existed for centuries. Wine started naturally does lend itself to being more complex and the truth is not just in the research it is in the taste. Go out and buy a 2003, 2004, or 2005 Labyrinth Bien Nacido Pinot Noir and Lane Tanner Bien Nacido Pinot Noir. They were made from the same grapes from the same block and were picked at the same time.  While they are both beautiful expressions of a great vineyard the Labyrinth, which was started naturally and then inocculated, is definitely more complex and the reason for this is because of the large number of different microbes that begin the fermentation. End of story. Nothing else matters.

All research and opinions about terrior and complexity aside, the number one reason I am opposed to fermentations started by innoculating with cultured yeasts is that you are destroying one of the most beautiful aspects of wine. God created the grape with the unique ability to attract and collect yeast on the skin of the grape. This is called the bloom and I can not understand why people overlook this miracle. In order to innoculate most vinters dose the wine with So2 which in turn kills off the yeast population present on the skins. To me this is a travesty and it helps destroy the soul of the wine. I encourage vintners to let the fermentations start naturally. This is the beauty of wine. This is what seperates wine from other alcoholic beverages. If you are worried about the fermentations finishing dry then you should think more about picking at lower brix levels and you can always add yeast towards the end.

Comments

[Jeff @ make wine]

I think you are correct Adam. People have been making wine for thousands of years. A part of me wants to believe that the wine made in the days of Rome was just as good if not better than the wine we are creating today. And they were not using any sort of scientific yeast. The whole idea of combining science with yeast and wine is just a turn off for me.

[Arthur]

Adam

You should read my three-post series about the issue of "wild yeasts" more closely. Perhaps then you will see that my summary of the topic is more ambiguous than one-sided.

There are many unanswered questions in this topic and one of them is how does S. cerevisiae get on the grapes to begin with - since the vineyard is not a good environment for this yeast. While I agree that a question can dictate its answer and data can be interpreted differently or put in a different light, I make a point to address the deficiencies in what we know about S. cerevisiae in the wild in my posts.

[Adam]

Jerry,
I agree that there are many variables in the winemaking process and they all affect the wine in a different way.

I do not believe that time on skins for the pinot noir grape will lend to a vast difference between the two wines unless it is a difference of, lets just say, for the sake of argument, 10 or more days. My point is that it would have to be more than a few days difference, which if I were guessing on this particular wine is more like a 1 or 2 day difference, but I will write the winemakers and find out for you.

The means and frequency of cap manipulation were very similar as they both simply employed minimal punch downs daily.

Peak and average temperature of the fermentations were similar and the fermentations finished just a couple days apart.

Both were aged in new and used traditional french oak barrels.

I will find out about the elevage for you but I am certain that it is very similar as well.

The wines I mentioned are made by a husband and wife and are handled virtually identically except for the fermentation regimen.

You are right, the wine does tell a story, but it should just tell the story of the land. That is my point in all of this. Let the wine speak of just the land.

Yes I believe the organisms that are present on the wine skins are desirable in the finished wine. I am not opposed to adding yeasts towards the end of the fermentations, but I believe wine should be allowed to begin to ferment the way God intended. It is part of the beauty and mystery of wine!

[Jerry D. Murray]

Adam,

No offense intended but there are likely many differences in how these two wines were produced. Days on skins, means and frequency of cap manipulation, peak and average fermentation tempeture, size of fermentation vessel, cooperage, handling during elevage, etc can all have a tremendous impact on a wine. Are all of these variables the same?

I am by no means stating that you are in anyway wrong in declaring one wine more complex than the other, I haven't tasted these wines so I will defer to you. However I do think chalking this difference in complexity up to differences in yeast alone is problematic.

I agree the truth is always in the taste but the wines tell the story of everything that they have experienced not just one aspect. Though the wine tells us what it has been through there are simply elements of that story that we ( the editorial we ) cannot understand.

Again I will ask; are all of the organisms living in Must at the begining, during and end of fermentation desirable?

[Adam]

Jerry,
I am referring to the wines mentioned in the previous sentence. The Bien Nacido Pinot Noirs offered by Lane Tanner and by Labyrinth. The only difference is the way the fermentations were started. The "nothing else matters" quote refers to the taste. The truth is always in the taste.

[Jerry Murray]

"reason for this is because of the large number of different microbes that begin the fermentation. End of story. Nothing else matters." Are you implying that the other decsions made by winemakers have no bearing on a wines complexity?

Also SO2 is considered much more of a microbiostatic than a microbiocide, so there is some doubt as to it ability to "kill" the microbes you speak of. Are you sure that all of those microbes are desirable? At what point does "complexity" become a flaw?