August 17, 2017

Research On Hybrid Tannins Continues

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This is the first installment in a two part series about tannins in hybrid grapes and wine. 

Bring on the tannins (or lack thereof)! Are you ready for a rip roaring whirlwind of a story? I felt compelled to write a follow up to the initial Midwest Wine Press tannin story because fortunately for us, the research efforts of Dr. Gavin Sacks and Dr. Anna Katharine Mansfield of Cornell University are a 1-2 combo that just won’t quit and their research endeavors are very much worth sharing.

To bring everybody back up to speed of what was discussed in Part 1 of the Red Hybrid Tannins article (July 2013), we took a brief look at tannin nomenclature and discussed why having tannin structure is integral to forming the backbone of a dry red wine. In limited detail, we discussed the drastic difference in tannin concentration between red French-American hybrids and red V. vinifera. Furthermore, since tannins were of obvious quality importance and limiting in quantity, tannin augmentation options were explored – more on this topic below.

Ready, set, go!

At the heart of the matter is this question: why are grape derived tannins lower in red hybrid wines than in V. vinifera wines? And on this subject there is new research stemming from Dr. Gavin Sacks’s (Associate Professor, Department of Food Science) lab in conjunction with his graduate student Lindsay Springer1. This new body of work systematically quantified the difference in tannins (for both grapes and wines alike) between hybrids and V. vinifera and detailed possible tannin limitation mechanisms (aka tannin binders). But before we delve into this topic, I want to take a step back and touch on new nomenclature for hybrids that I think will be of interest to most.

The French-American (FA) hybrids (Maréchal Foch, Leon Millot, etc.) were the result of intensive breeding efforts during the late 19th and early 20th century in response to the phylloxera outbreak that almost wiped out the cultivation of V. vinifera in Europe. Time or more specifically history separates the FA hybrids from more modern crosses stemming from Cornell, University of Minnesota, Elmer Swenson, etc. However, the more distinguishing feature presented here is the crossing pedigree. FA hybrids differ in pedigree to the Neo-American (neo) hybrids in the sense that FA hybrids are more direct descendants of V. vinifera than the Neo hybrids – even though the overall percent V. vinifera genetic makeup may be roughly the same (~50%). For instance, Baco Noir (a FA Hybrid) is a direct cross of Folle Blanche (V. vinifera) and V. riparia (American), whereas Neo hybrids, like Frontenac or Corot Noir, are a cross of hybrid with another hybrid or American variety. Somewhere down the line there are bits and pieces of V. vinifera parentage here and there. So FAs vs. Neos vs. V. vinifera, got it? Good.

Back to tannins (I love me some tannins)

First, Springer and Dr. Sacks surveyed 12 V. vinifera wines and 12 hybrid commercial wines from the Finger Lakes of Upstate New York. Before I forget, herein we are only talking about tannins in red grapes and wine, not whites. On average, as measured by Adams-Harbertson Tannin Assay, V. vinifera wines had 255 mg/L (or ppm) Catechin Equivalent (CE) of tannin vs. only 61 mg/L CE of tannin in hybrid wines.1 Interestingly enough, one outlier hybrid wine (Vincent) was found to be on par with the >200 mg/L CE tannin benchmark of V. vinifera wines surveyed. On a side note, tannin concentrations in V. vinifera wines stemming from the Finger Lakes were roughly half the amount of V. vinifera wines surveyed in another study stemming from warm or hot growing climates like California, Washington, Oregon and Australia.1 This finding highlights what a difference growing climate (think heat accumulation, sunlight penetration and precipitation) can have on overall tannin concentrations in red grapes and consequently wines.

Recall that wine tannins are chains of smaller building blocks (flavan-3-ols), and when scientists chop these chains up they can get a sense of how short or long the chain is, a term referred to as mean degree of polymerization, aka mDP. Dr. Mansfield (Associate Professor, Department of Food Science), noted in her recent Northern Grapes Webinar (Building the Perfect Body: Tannin Strategies for Red Hybrid Wines) that red hybrid wine tannins are also on average shorter (2.26 – 3.21 mDP) than V. vinifera (7-13 mDP).2

Alright, so point taken yet again. On average, red hybrid wines are indeed low in tannin and of what little tannin is present, it seems to be shorter in length, which could potentially lead to more bitter than astringent properties in wine.2

Ok, but why?

Further exploration into this matter took Springer and Dr. Sacks back into the lab, in a more controlled setting where the duo could quantify and trace tannin concentrations from harvest to final wine production.

The experiment included four FA hybrids (Leon Millot, Marechal Foch, DeChaunac, Baco Noir), two Neo hybrids (Corot noir, Noiret), and six V. vinifera (Pinot noir, Merlot, Lemberger, Sangiovese, Cabernet Sauvignon and Cabernet Franc).

Not all too surprising, in this experiment, wines made from hybrid grapes resulted in less wine tannin – specifically FA hybrid wines were less than Neo hybrids, and Neo hybrids were less than V. vinifera wines. However, Noiret (a Neo hybrid), was the major outlier for hybrids measuring in at a whopping 354 mg/L CE of wine tannin, putting its wine tannins shoulder-to-shoulder with the best of V. vinifera wines (Pinot noir and Cabernet Sauvignon) analyzed in this experiment.1

On average, less wine tannin was indeed derived from varieties that had less grape tannin. But what was surprising to the researchers was how little grape tannin made its way into the wine. In other words: the concentration of wine tannin was significantly less than expected given the concentration of measured grape tannin. Could something other than grape tannin have an inhibitory effect on overall wine tannin concentrations? It seemed likely.

Researchers confirmed that a significant portion of grape tannin was being lost elsewhere during wine production. In fact, while there was certainly significant less measured grape tannin in FA hybrids than in V. vinifera, the disparity between the two grape classifications was three times greater at the wine level!

Upon further data analysis, extractability, or the percent of grape tannin that was extracted into wine, was significantly different for each grape variety. In general, the FA hybrid wines had the lowest amounts of extractible tannin (2.2-5.7%) while Neo hybrids were quite variable (2.2-26.1%) as were V. vinifera varieties (8 – 22%). Once again, the one major outlier was Noiret, which had 26.1% tannin extractability, the highest percent tannin extraction across all varieties analyzed! 1

To summarize these results, Noiret was able to achieve one of the greatest measured concentrations of wine tannins because it had the greatest percent tannin extraction despite having middle-of-the-pack grape tannin concentration. Again this was an aberration to all other hybrids (FA or Neo), in which the other hybrids suffered in the wine tannin department either because of low grape tannin concentrations and/or low extraction rates.

Cheers!

Piero Spada received his MS from Cornell’s Viticulture and Enology program and was previously a winemaker in the Finger Lakes. Piero is now a Midwest vineyard and winery consultant and can be reached via email at pierospada.com 

Sources/Additional Reading:

  1. LF Springer and GL Sacks, 2014. Protein-Precipitable Tannin in Wines from Vitis vinifera and Interspecific Hybrid Grapes (Vitis): Differences in Concentration, Extractability, and Cell Wall Binding. J. Agric. Food Chem.
  1. AK Mansfield. 2015. Building the Perfect Body: Tannin Strategies for Red Hybrid Wines. Northern Grapes Project Webinar

https://www.youtube.com/watch?v=fEYAk0WkgaI&feature=youtu.be

  1. 2014 Scott Laboratories Fermentation Handbook
  1. LF Springer and GL Sacks. 2015. Of Terroir and Tannins: The Role of Pathogenesis-Related Proteins in Red Wine Astringency. Abstract. ACS: Division of Agricultural and Food Chemistry Graduate Symposium.