Issue #15

Wine Funky Smells and Other Weird Tasting Science News

Happy Month of May! I am quite happy this first quarter is over and to finally get back to my favorite weekend activity, writing to you about wine tasting. Long story short, I had to take care of family matters back in France and some challenging projects at work.

That’s why I haven’t kept on my promise to deliver a monthly newsletter in your inbox and I apologize.

In this issue of Wine Tasting Tips, you will discover:

* The two animals you don’t want to smell in your wine

* Physics principles of wine tears

* Why you may also smell with your tongue

* My 3 Wine Tasting Tips

The two animals you don’t want to smell in your wine

An article in the San Francisco Chronicle caught my eye with this title “Did Mandy Heldt Donovan just ruin her wine? Why the Napa winemaker intentionally added brettanomyces — a spoilage yeast — to her Pinot Gris”.

Hmm…, Brettanomyces bruxellensis is a yeast that usually winemakers do their best to avoid and are very paranoid about getting close to their winery. Indeed, aromas of manure, Band-Aid, horse sweat are not particularly pleasant to smell in wine.

The winemaker explains she was curious to learn if she could use this yeast as a winemaking tool, especially since it is quite popular in craft beer making.The story goes on to reveal that Donovan was a student of Dr Linda Bisson, a renown yeast geneticist from the University of California, Davis.
What do we know about Brett yeast and its impact on wine?
I went back to the work of Dr Bisson, especially to her work on Brettanomyces. She indeed developed the Brett aroma wheel with collaborators C.M. Lucy Joseph andElizabeth Albino.

This work originated from anecdotal evidence that Brett sometimes imparted pleasant floral notes in wine. So Linda and her colleagues characterized the aroma compounds produced by 99 yeast isolates.

They found that all strains produced the two culprit compounds 4-ethyl phenol (4EP) and 4-ethyl guaiacol (4EG), under low oxygen conditions (like in a wine barrel) feeding on two amino acids called cinnamic acids. However, when feeding on other substates, different compounds were produced, and in total the scientists identified 44 compounds imparting a diverse spectrum of aromas.
An Aroma Wheel to Guide You
Inspired by Dr. Noble Wine Aroma Wheel, they organized these aromas on a wheel to help wine tasters identify if indeed the wine they are tasting expressed some Brett characteristics. The aroma descriptors were validated by 2 tasting panels. Below is a copy extracted from the report published in Catalyst: Creation and Use of a Brettanomyces Aroma Wheel.

If you are inclined to go deeper on this topic, I recommend reading this article “Two Decades of “Horse Sweat” Taint and Brettanomyces Yeasts in Wine: Where do We Stand Now?”. It not only covers the origin of the taint, but also some remediation techniques.

All article references are available at the end of this newsletter.

One off-flavor that is difficult to get tasters to describe in consensus is Mousey. It is also caused by Brettanomyces yeasts as well as other yeasts.

I remember when working at a winery, one of the senior executive was very sensitive to this taint and was annoyed when few of us could not detect it. He had this weird habit when he was suspicious of such a taint: he would put his palm on the glass rim, shake the glass from top to bottom and then smell the wine on his palm and confirm or not the presence of the taint.

Why is that?
The compounds responsible for this taint are not very volatile (namely 2-acetyltetrahydropyridine (ATHP), 2- ethyltetrahydropyridine (ETHP), and 2-acetyl-1-pyrroline (APY) ) to be detected in higher pH environment. A high pH environment would be when wine is swirled in mouth and get in contact with our saliva or when the wine gets in contact with the skin, in the case of the winery executive.

The “glass-palm” method is one way of minimizing variability among panelists. A recent group of sensory scientists tested other protocols and found better results only when the wine pH was adjusted to 5, which is difficult to do without a wine lab handy (Tempere et coll. 2019).

Have you heard about Oenodynamics?

Why mentioning Oenodynamics? I stumbled upon this article asking: “Why is your wine crying? Scientists say shock waves likely play a role”. The story is about R. Andrea Bertozzia, an UCLA mathematician, intrigued by the dynamics of the wine tears formation.

Check out a video demonstrating how wine tears are formed.

After swirling the wine in the glass, the wine coats the glass sides, and since the alcohol starts to evaporate first, the liquid goes up the glass side, dues to the surface tension being lower. Dr Bertozzia is searching how to model this phenomena. 
Over the years I found that academics will use a lot of efforts to include wine as their primary research focus. Why not?

Other Wine Tasting Science News

My 3 Wine Tasting Tips

#2: Shaking your Wine Glass Top to Bottom may Reveal a Mousey Taint

#3: Always Swirl your Wine Glass before Smelling and Tasting the wine Not only will you free the wine aromas and be able to detect them but you will be able to observe the dynamic formation of wine tears.

References used in this issue

Two Decades of “Horse Sweat” Taint and Brettanomyces Yeasts in Wine: Where do We Stand Now?

Comparison between standardized sensory methods used to evaluate the mousy off-flavor in red wine.

Why is your wine crying? Scientists say shock waves likely play a role

Swirling your wine is not pretentious; it’s just good physics

Humans smell with their tongues

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Cheers!

Isabelle