Using Dehydrated Grape Marc Waste to Improve Wine Quality: A More “Natural” Approach?

Producing a quality wine is of utmost important to winemakers, and arguably the most important goal in the industry as a whole.  There are many factors that influence quality in a wine, many of which are related to the chemical composition of volatiles and phenolic compounds, both which influence the sensory and overall quality characteristics of the finished wine.  Viticultural management and winemaking techniques can play a role in altering the concentration of these compounds, in addition to any biochemical reactions that may occur during the fermentation and aging processes.

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In addition to volatile compounds, which are associated with the aroma and flavor of wine, color plays an equally important role in wine quality.  In the “average” wine and poorer quality wines, color tends not to last as long as it does in higher quality wine.  In other words, color tends to degrade faster in average and low quality wines than it does in high quality wines.  This decline is tied in with an overall decline in the concentration of polyphenols in wine, which act to prevent oxygen degradation and other harmful reactions.  As a result of this, many average and lower quality wines must resort to adding greater quantities of SO2 and ascorbic acid in order to make up for the decrease in polyphenols that otherwise protect the wine.

With the increased push for more stringent ingredient labeling on wine bottles, and a general increased interest in producing more organic and/or sustainable wines, the use of more natural additives to protect wines again oxygen degradation or other “ailments” is of growing importance.

One potential candidate for a natural alternative to SO2 or ascorbic acid for the purposes of maintaining wine quality is waste grape marc from the juice industry and has been recently been studied for this purpose.  In the juice industry, grape marc (i.e. the skins and seeds waste) are collected after only a short period of maceration time (4 days touching the juice) than the maceration time of red winemaking.  This means that this marc has not yet been stripped of much of its chemical structure and components, indicating their possible ability to be reused and recycled instead of going to waste.

The goal of the study presented today was to determine if this grape skin waste in its dehydrated form could act as a new winemaking technique for increasing or maintaining color and for protecting the wine against phenolic and aromatic degradation prior to bottling.

Methods

Grape marc wastes were of Vitis vinifera grapes of the Bobal variety (red), and a mixture of the white variety Airén (70%) and an unknown red variety (blend hereby referred to as “AMIX”).  Marc was collected from a juice concentrate factory in Castilla-La Mancha (Julian Soler, Cuenca, Spain).   Marc was collected, frozen, then thawed, dried, then ground after the removal of seeds and stalks.  Four grape skin marc treatments were made for this experiment: 100% Bobal, 100% AMIX, 75% AMIX & 25% Bobal, and 50% AMIX & 50 Bobal.

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Two aged and two young wines were provided by a local winery.  Young wines were meant to correspond with bulk commercial wines with a shelf life less than or equal to three years.  Young wines were made using traditional methods, and with 5-10 days of maceration and fermentation in stainless steel tanks.  Wines were blends of grapes found in the area, including Tempranillo, Cabernet Sauvignon, Merlot, etc.  Aged wines were created similar to young wines, except these underwent a longer maceration time (10-20 days) and were aged for at least 6 months in American oak barrels.

All wines had a pH between 3.5 and 3.9, and alcohol content between 13.5 and 14% vol.  Wines were bottled in amber bottles with synthetic cork closures (4 bottles of each wine made).

For maceration with the grape skin marc treatments, wines were macerated with 5g/L of the treatment over 3 days at 18oC.  After maceration, grape marc treatments were removed with a strainer and the wines were stored in crystal bottles at 18oC.  Analysis of the wines occurred immediately after maceration, then at 3 months and 6 months post maceration.

Color parameters (anthocyanins) and total phenolic compounds were analyzed using UV-vis spectrophotometry.  Individual phenolic analysis occurred using HPLC-DAD.  Finally, volatile compounds were measured using SBSE-GC-MS.

If you want to know more details about the methods, please ask!

Results

Color

  • The addition to grape marc in wines significantly impacted the color intensity and shade of all wines (both aged and young).
    • Bobal showed the highest color intensity increase, which AMIX showed the lowest.
    • The extent of color intensity increases were dependent upon the type of grape used to make the dehydrated grape marc powder, though all grapes led to an increase in color.
      • These results indicate the addition of grape marc waste prior to bottling may improve the color in both aged and young wines.
  • All grape marc treatments cause a decrease in shading, which is indicative of higher quality.
    • The Bobal treatment appeared to be the most effective in reducing shading in wines.
    • The mixture of Bobal and AMIX treatments were not as effective in reducing shading in wines.
  • Color intensity increased over time in all wines.
    • Bobal wines showed the highest increase over time.
  • Shade values increased over time (degradation in quality) compared with controls.

Total Phenols

  • Total phenols significantly increased after grape marc treatment.
    • Bobal treatment showed the highest increase, followed by the mixtures of Bobal and AMIX.
    • Increases were higher in aged wines than young wines.
    • Total phenols evolved over time in the same pattern for grape marc treated wines as control wines.
    • All wines treated with grape marc had significantly higher total phenol levels than control wines
      • Total phenol levels were similar for all grape marc treatments, with no one treatment performing better than the rest.

Anthocyanins

  • Grape marc treatments resulted in an average increase of 50mg/L of total monoglucoside anthocyanins.
    • Bobal produced the highest levels of anthocyanins, while AMIX produced the lowest.
    • Anthocyanin levels decreased over storage time.
      • AMIX and the mixture with more AMIX showed the lowest decrease in anthocyanins.
      • The amount of anthocyanins present depended upon the grape marc treatment and on the age of the wine.
  • Even though anthocyanins decreased over time, the anthocyanin content in grape marc treated wines was always higher than control wines, and remained significantly higher by the end of the experiment.

Low Molecular Weight Phenolic Compounds

  • Treatment with grape marc significantly increased the levels of low molecular weight phenolic compounds in all wines.
    • Mixtures of red and white marc appear to have increased these values the most, compared with white or red varieties by themselves.
      • The authors concluded that mixtures of grape marc could be good strategy for balancing phenolic compound deficiencies in wine.
      • Also, using different mixtures of grape marc could allow winemakers more control over aroma and flavor profiles of their wines by adjusting the proportion of one particular skin over another.
  • The primary low molecular weight phenolic compounds released by the grape marc were gallic acid, catechin, epicatechin, and resveratrol.
    • Caffeic and coumaric acids increased more in young wines than aged wines.
    • Resveratrol increased more in young wines.
  • After 6 months of storage, all wines treated with grape marc had higher levels of low molecular weight phenolic compounds than controls.
    • Grape marc mixtures with greater levels of white grape skins produced wines with the highest levels of low molecular weight phenolic compounds.

Volatile Composition

  • After grape marc treatment, the volatile compound β-ionone significantly increased in wines.
    • The Bobal treatment resulted in the greatest increase of β-ionone.
    • After grape marc treatment, β-damascenone and nerolidol decreased in all wines.
      • Even though β-damascenone levels decreased, they were still above their odor thresholds, thus maintaining their floral and fruity characteristics.
      • 1-hexanol (herbaceous tones) remained unchanged after grape marc treatment.
      • After grape marc treatment, increases in isoamyl acetate (banana tones) were noted.
      • Wood-derived compounds remained unchanged after grape marc treatment.

What does this all mean?

Overall, the results of this study indicate that using dehydrated grape skins/marc from the juice industry may be a important tool for increasing the quality characteristics of average or lower quality wines prior to bottling.   Specifically, after the treatment with dehydrated grape skins, color and total phenolic content increased in all wines, as well as anthocyanins and low molecular weight compounds, all of which are important contributors to wine quality.  The volatile component of the wine was only moderately affected, indicating that if particular flavor profiles are desired, then the winemaker must be deliberate in exactly which variety of grape(s) is used in creating the dehydrated grape skin treatment.

I found the results of this study very fascinating, and important in the quest for finding more natural alternatives to preserving or increasing quality in the winemaking process.  One thing that is missing from this study, however, is the sensory analysis of the treated wines.  Does dehydrated grape skin treatment affect the flavor and aroma of the finished wine?  Based on the results from the volatile compound analysis, the answer should be yes, however, I would have liked to see the accompanying sensory analysis for confirmation.

In lieu of space, I won’t go on regarding more specific results or implications; however, I’d love for you all to help me continue the discussion in the comment section below.

What do you think of the study results?

What implications to you see for this type of treatment application?

Is there testing that you would like to have seen that was not performed?

Do you think the treatment of grape marc waste is, in fact, a natural approach?  Or something different?

Please feel free to leave your comments/questions for discussion!

Source: Pedroza, M.A., Carmona, M., Alonso, G.L., Salinas, M.R., and Zalacain, A. 2013. Pre-bottling use of dehydrated waste grape skins to improve colour, phenolic and aroma composition of red wines. Food Chemistry 136: 224-236.

DOI: 10.1016/j.foodchem.2012.07.110

I am not a health professional, nor do I pretend to be. Please consult your doctor before altering your alcohol consumption habits. Do not consume alcohol if you are under the age of 21. Do not drink and drive. Enjoy responsibly!

11 comments for “Using Dehydrated Grape Marc Waste to Improve Wine Quality: A More “Natural” Approach?

  1. September 26, 2012 at 9:07 am

    You had me at “Dehydrated Grape Marc”

    Really interesting. It appears to this eye to be a form of uber-ripasso, in the simplest terms I can muster. I’d love to know more and try wines from this method.

    Grazie

    • Becca
      September 26, 2012 at 9:46 am

      Thanks for your comments, Alfonso!

      I, too, am very curious about trying wines made by this method. I am uncertain of anyone producing commercial wines at this point that utilize this technique, but I’m thinking we may start seeing some experimentation in the future, particularly with home winemaking and small batch operations.

  2. September 26, 2012 at 3:27 pm

    Fascinating, indeed. Have to agree with Alfonso – when you take all the fancy chemistry away, it’s appasimiento on an industrial scale. I, too, would be interested in the sensory analysis on these wines, though I would join you in suspecting that they experienced some appreciable benefit beyond megapurpling.

    Having recently returned from Italy, I am once again reminded how we (in the US) continue to learn lessons mastered millennia ago by ancient civilizations…cultures that long ago learned to make do with little are experts in finding value in what would otherwise be discarded. And so it goes with the pommace. (http://bit.ly/OhGIl4)

    Terrific piece! Now, can we get our hands on some of those wines???

    • September 26, 2012 at 6:26 pm

      Thanks for your great comments, Steve! I have yet to experience a wine made using appasimiento techniques, though this post and your (yours and Alfonso’s) comments really got me thinking about trying some. You’ll have to give me some recommendations for wines done in that style that are available in the US (if any). Otherwise, we’ll have to just wait and see how long it takes for this method to be performed on a commercial scale!

      • September 27, 2012 at 9:40 am

        Though appasimiento is applied more broadly than in just Valpolicellas, these are (IMHO) the most illustrative examples of the process. Alfonso has better knowledge and recommendations as to what might be available in your market, but given how limited the production of these wines are, you’re probably best off just asking your favorite local retailer.

        That said, I would suggest, if you can, putting your hands on two “sibling” Valpolicellas: one Amarone and one Ripasso from the same producer. The concept will click easily in the glass when you taste these side-by-side. If you don’t have the appetite for the price tags (Amarones are not cheap), see if you can find a straight Valpolicella and its sibling Ripasso from the same producer.

        The two mentioned in this piece are lovely examples and terrific values: http://bit.ly/OhGIl4

        Happy field work!

        • Becca
          September 27, 2012 at 1:06 pm

          Thanks for all the great information and advice, Steve! I think I have a solid base to start from in my search.

          Time to go drink some wine FOR SCIENCE! :)

  3. James McFadyen
    September 26, 2012 at 7:59 pm

    This is riveting stuff, it is good to see uber recycling considered in the grape/wine growing/making industry to improve the quality of wines drunk by the majority of wine consumers!
    It reminds me a little of the Australian research done into breaking must or post fermentation wine into its components, and restructuring the wine to give exact results year on year for large volume brands.
    Nice to see some good research into self regulation, and removal of any extraneous additives to the beautiful bottled poetry we call wine!

    Sante

    • Becca
      September 26, 2012 at 8:09 pm

      Thanks for your comments, James!

      I completely agree it’s great to see research focused on recycling/sustainability/etc. There is a lot of waste in the juice and wine industry, so what better way to deal with it than to use it over and over again until all the resources are exhausted.

      I’m so glad you enjoyed this post!

      Cheers!

  4. September 27, 2012 at 8:20 pm

    I had the same thought as Alfonso – sounds similar to some effects of the ripasso method, although that’s as much to do with the nutrients in the pomice as the color, mouthfeel, aromatics etc. So perhaps the results might be similar with ripasso? It would be interesting to do an A-B comparison of the same must – one fermented using ripasso and one without, to which is added some marc post-fermentation. It would be interesting to see which had better results to color, aromatics etc.
    One downside to this is the quality of the marc you could get. I’m not convinced that getting a bunch of marc from a red concord grape would be that beneficial, or that what it might add would even be appreciated…
    Cheers!

    • Becca
      September 27, 2012 at 9:23 pm

      Great comments, Marty!

      I agree about the potential downside of using lower quality marc. Perhaps one would have to be a little more selective than what would be ideal in regards to reusing/recycling. That would actually be an interesting follow up to this study: testing many different types of marc (more than just the two that they did study) including both concord and vinifera varieties.

  5. Andrew
    March 8, 2014 at 2:55 pm

    Many people simply add commercial tannin products which are made from grape Marc. Dehydrated grape marc is just the first step in that process. The philosophy here is quite different, but ultimately I think they are not really worlds apart.

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