FARMVIEW Video Transcript

EPISODE 6 - The Wine Grape Tannin Research Project

Voice Over: Tannin is one of a number of compounds that contributes to the sensory characteristics of wine including mouth feel and astringency in wine. Studies have shown that being able to quantify and predict compounds such as anthocyanin content and tannin composition prior to harvest may develop an understanding of how this translates into the completed wine and its final quality.

The Wine Grape Tannin Research Project that is being undertaken at DPI Mildura aims to develop robust methods of measuring tannins pre harvest and to investigate the viticultural, environmental and varietal factors that affect tannin content and composition in Australia’s premium wine grape varieties.

Senior Research Scientist and Section Leader of Plant Production Science at the DPI Mildura, Mark Downey is head of the research project.

Mark Downey Interview:

While in some cases anthocyanins was a good indicator of wine quality when you measured it in the grape, but it wasn’t always reliable and so what we thought we needed was another measure and tannins was the next obvious thing to measure what we thought tannins were a good thing to measure because there was so much of it and it was fairly easy to measure. But the problem with the industry was there wasn’t a lot of published material on tannins. Not on tannin levels, not on how they change, not on how much variation there was across different varieties, sites and seasons and all that. So we thought we’d write a project to explore some of that, see how much tannin was there and how that much it changed with time, with cultivar and things like that.

So it is quite a complex picture but tannin itself creates/generates quite a lot of that mouth feel component, you know it is a very big contributor to wine quality.

We mainly are focusing on the grape, you know, how viticultural practice and how you know site and season influence the levels of tannin in the grape.

Voice Over: Mark has made links with fellow Tannin researchers from the United States and 2 of these researchers, Mark Kelm from Constellation Wines and Jim Harbertson from Washington State University recently visited Mildura to share their knowledge and techniques with Mark and his team.

Mark Kelm from Constellation Wines is currently investigating anthocyanins, tannin and related chemistries in wine and grapes and explains the way that they can isolate and measure tannin levels in grapes using High Pressure Liquid Chromatography- HPLC.

Mark Kelm Interview:

In many ways its groundbreaking research, the technology that I have developed, the HLPC, has been applied to chocolate in a former job, now I am applying this towards grapes. Grapes are a different animal; grapes are much more complex to cocoa, so it’s uncharted territory in a lot of ways.

The focus was to look at tannins, tannin chemistry in wine and grapes. You can isolate the compounds that come off the system, so you take a complex mixture, contains anywhere from tens to hundreds to even thousands of different compounds, the instrument allows you to separate them and then also to isolate those individual compounds or groups of compounds for further analysis and further experimentation.

We isolate them as best we can, and then we check the purity on analytical HLPC on a much more precise instrument for determining the purity of these compounds if we hone in on individual groups of compounds or singular compounds for further research.

Voice Over: Jim Harbertson from Washington State University is currently working on assessing astringency using both chemical and sensory methods as well as characterising tannin, anthocyanins and polymeric pigment levels.

Jim Harbertson Interview:

Mark Downey and I have known each other for a few years now and we both sort of have a similar type of research bent, and we both are very interested in understanding what causes the tannin astringency’s effect in wine and how to manage it from the grape growing type standpoints and also the winemaking type standpoints which I am more focussed on than Mark is….. so we are all very interested in sort of finding out what the information means and how we can translate that into the best type information for people can use, the most easy translatable information that people can use, like big decisions like, when to press your wine so it is the right astringency that you want to finish whatever your looking for, that’s the type of information we are trying to do.

What Mark Kelm has brought here and Mark Downey has brought this new preparatory stage HLPC and they are going to separate all these tannin molecules apart from each other and what I’ve been doing is using this protein precipitation method for a long time which basically, so astringency that we taste from wine, is like in reaction between from the tannins and the salivary proteins in your mouth and the salivary proteins precipitate out, normally the salivary proteins are lubricating your mouth, suddenly the tannin’s there, the proteins are gone, and now you have this mouth feel because suddenly your tongue and your cheek are painfully aware of each other.

With the preparatory phase HLPC we can now start defining these things a little bit more clearly, it has to be above 4 or 5 or whatever it needs to be and then we can start saying, start looking into the fruit how is this type of vineyard effect can change the tannin polymer composition so we can have larger ones of whatever you need to know, or winemaking technique for that matter. So now we can start understanding these things a little bit more at the very basic level that we have been sort of making assumptions about.

Voice Over: To date, a number of unsuspecting results have been uncovered including variations in tannin levels between cultivars, the composition of the tannin and its pattern of accumulation.

Mark Downey Interview- (Results and future direction)

There have been a few outcomes that have surprised us; the biggest shock was the range of tannin levels across grape cultivars, the surprising things in that was some of the cultivars that had really high levels of tannins were things that we didn’t really expect things like table grapes like Red Globe, Red Emperor. From the work that we originally did in South Australia there is a pattern of tannin accumulation that goes up from flowering and fruit set to around veraison which is the onset of ripening and then tends to decline towards harvest, and we thought that was a universal pattern and other people had seen similar pattern and then we came up here and we started doing this analysis in a warm region and we see that that peak is out around fruit set, increased to fruit set but then it declines rapidly almost to its lowest level by veraison and stays at that level more or less until you harvest it. So where we were thinking perhaps is that period of decline was something you could manage during ripening…in a warm region you can’t because it is already over very early in the season, so that was a real shift and that caused a few us to think about how would you go about managing tannin if it is happening so early in the season and even question if it is something that is determined in the previous season the same way fruitfulness is. So they are interesting questions we need to pursue.

One of the things we would really like to look at is can we shift that peak by any management tools that we’ve got, like irrigation or nutrition, canopy management, timing of pruning, and things like that.

But if we could increase the quality of fruit in the vineyard, we could make better wines from it. I think that the real importance of that is, in such a competitive world as the global wine market, if we can raise the quality of our wines in their current price points, it means that over time we can raise them into higher prices points and that’s obviously an economic return to the country as well as to the industry and the individuals involved in the industry and I think that that’s the real long term benefit of it.

Voice Over: Questions for the research that remains are:

• What levels of tannin in wine grapes are desirable for winemaking?
• What tannin composition is most desirable for a given wine style?
• How do we manage tannin in the vineyard?

Industry involvement in the research is important to the outcomes of understanding the effect of tannin variability in wine grapes. For further information about the wine grape tannin project, please contact Mark Downey mark.downey@dpi.vic.gov.au