Sept 2018: Making Wine with Underripe Fruit

This season has included many challenges in the vineyard that are now translating to the winery. Many of the red grapes being picked are less ripe than desired. 

Overall, a winemaking philosophy of maximizing fruitiness and minimizing astringency may be a good focus when working with underripe grapes. There is no magic bullet to make underripe grapes taste ripe. However, there are a few things to think about when planning your winemaking to respond to this vintage.

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A little background chemistry

Chemically, there are several issues that may come up with underripe red fruit (Mosson et al 2016):

  • Decrease in fruity aromas and flavors

  • Less extractable phenolics leading to lighter color and palate weight wines (Zoecklein #61)

  • Less ripe tannins in skins and seeds and greater extractability of seed tannins, which can lead to bitterness and unpleasant astringency (Zoecklein #61, Casassa and Harbertson 2016)

  • 6-carbon alcohols and aldehydes that contribute aromas of cut grass, herbaceous, crushed leaf, and bitter flavor (Chauffour 2017, Mozzon et al 2016)

  • Methoxypyrazines in some varieties, especially Cabernet Franc and Cabernet Sauvignon impart vegetal, green pepper aromas and flavors

  • Low molecular weight (volatile) sulfur compounds can amplify vegetal aromas from the above compounds (Zoecklein #114, Mozzon et al 2016)

An additional issue of concern is the balance of structure and texture in wine. Zoecklein (#94) argues there is an inverse relationship between sweetness/body and acid/phenols such that an increase in one component leads to a perceived decrease in the other.  This means as astringency increases, perception of sweetness decreases. Sweetness and body are affected by alcohol, polysaccharides, and fruit intensity while acid and phenols include tannin intensity, astringency, and bitterness. Methoxypyrazines increase the perception of tannin intensity.

Underripe grapes can lead to unbalanced wines in several ways:

  • Less sweetness due to low alcohol and less fruit character

  • Higher perception of astringency due to higher acids and harsher tannins

Highly extracted wines made from underripe grapes will be unbalanced. This leads to winemaking decisions that limit extraction of astringent compounds and boost elements of sweetness (short vatting) (Zoecklein #78).  

Sweetness can be increased by the addition of polysaccharides and by increasing alcohol (through chaptalization). Several enological companies sell yeast derivatives that can be added to the fermentation to improve colloidal balance/polysaccharide availability (Chauffour 2017, Scottlabs). Polysaccharides can also be boosted in the form of additions post-fermentation.  

Chaptalization alone has been shown to decrease the perception of underripe flavors. Casassa and Harbertson (2016) studied the effect of ethanol concentration on seed tannin extraction in Washington State Merlot. They found that the degree of seed tannin extraction was the same with different ethanol concentrations (from 11.7% to 14.4% ABV), and that chaptalization reduced the sensory perception of vegetal character found in wines made from underripe fruit.  They postulate this effect is due to increase in solubility and volatility of aroma compounds with increasing alcohol. In a separate study (Sherman et al 2018), chaptalization of wines harvested at 20 brix were originally described in sensory analysis as sour and green.  Chaptalized replicates of this juice were fermented and the resulting wines were described as fruity and sweet. The authors conclude that “wine ethanol concentration is more important for the sensory profiles of wines than is fruit maturity at harvest.”


Specific Winemaking Suggestions

  • Limit exposure to stems, seeds, and skins. Destem, don’t crush the berries. 

    • In Cabernet Sauvignon, 53% of the pyrazines are found in stems, 31% in seeds, 15% in the skins and 1% in the flesh (Enology Notes 114).  Pyrazines have been found to be very extractable, with all of the pyrazine found in the finished wine already present in the first 24 hours after crushing. This extraction does not require alcohol, and the amount of IBMP was not affected by the frequency of pumping over (Roujou de Boubee et al 2002).

    • Carbonic maceration (leaving berries uncrushed) limits the production of C6 aldehydes and alcohols and the extraction of harsh seed tannins (Mozzon et al 2016).

  • Cold soak: There are conflicting theories on this. Some sources advocate limiting all exposure to limit extraction (Scottlabs) and limit formation of C6 aldehydes by peroxides (Mozzon et al 2016), others (Zoecklein #81) feel this is a good time to extract color.

  • SO2: Generally, SO2 leads to greater extraction of color, so a higher SO2 dose may be helpful here. However, SO2 may also lead to reductive odors, so take care to aerate the fermentation if you have used a larger SO2 dose. 

  • Enzymes 

    • Enological companies advocate the use of enzymes to help with extraction of color and polysaccharides.  These enzymes break down the cell walls and membranes of grapes to allow release of cellular components. (Chauffour 2017, Scottlabs, Zoecklein #78)  This is more important if you are planning to press early and/or limit cap management.

    • Be careful in your choice of enzymes. Some are formulated to extract more tannin (descriptions will talk about longer aging), while others are formulated to limit tannin extraction (descriptions will emphasize fruity flavors and color).  Choose the gentler option, and use a lower dose. Contact your product rep if you are not sure.

    • It is important to note that if you use enzymes, these should be added at a different time than any tannin or SO2 additions, as they will be inhibited by both.

  • Tannins may be added at the crusher or after the beginning of fermentation to help stabilize color. Since you are limiting contact with stems, seeds, and skin, tannin will be in short supply and color may be lost.  Make sure to choose the option that is for color stabilization rather than those for long-aging wines. 

  • Yeast

    • Factors to consider in your selection of yeast strain should include maximizing fruit expression and polysaccharide production (for mouthfeel) and minimizing vegetal aromas. If you are planning to do a hot fermentation, make sure your yeast strain can handle the heat. A consistent, non-labored fermentation is important to minimize production of volatile sulfur compounds (which amplify veg), so either choose a low nutrient yeast or feed the fermentation as needed.

    • Pickering et al (2008) spiked juice with IBMP and fermented it with four different yeast strains (EC1118/Prise de Mousse, BM45, D21, and D80), then measured the IBMP levels and sensory perception of green characters after fermentation. They found that after fermentation, BM45 wine has 29% more IBMP than prior to fermentation while the other three maintained the same level. In sensory tests, D80 had the highest scores for vegetal/green aromas and D21 produced wines with low green characters and high “jam” and “red berry” descriptors

    • Some 6 carbon alcohols and aldehydes can be enzymatically transformed to thiols during fermentation. A thiol-producing yeast for red wines will increase fruit and decrease vegetal characteristics (Mozzon et al 2016).

  • Temperature: There are two schools of thought on this. 

    • One emphasizes the need to retain fruity aromas to counter vegetal aromas, maintain healthy yeast, and avoid over extraction of harsh (underripe) tannins.  This means a lower temperature (75 degree F) fermentation. (Zoecklein #78, 81)

    • Another school of thought expresses the idea that higher temperature fermentations can volatilize or transform some pyrazine, and will do a better job extracting phenolics to add body to the wine.  These advocate fermenting up to 90 degrees (Bogart and Bisson 2006, Chauffour 2017, Gardiner 2014).  However, some fruit aromas may be lost during hot fermentations.

    • In the balance, it seems that the high temperature school is addressing pyrazine specifically, while the low temperature school is addressing several aspects of underripe fruit. If you are primarily worried about pyrazine, ferment hot. If you are also concerned about body and overall fruit flavor, ferment cool. 

  • Oxygen

    • Aeration can have a positive affect by preventing the formation of reduced sulfur compounds, improving the health of the yeast and contributing to the fixation of color and polymerization of tannins.(Chauffour 2017, )

    • However, oxygen can take away from fruity thiol flavors that will help overcome herbaceous flavors, and contribute to the formation of C6 aldehydes.

    • Aerate conservatively, at the peak of fermentation, but stop aeration when fermentation slows down.

  • Maceration

    • Limit maceration time in order to limit extraction of harsh phenolics. Press early, even before the completion of fermentation. Seed tannins are more soluble in alcohol, so the less time they are in contact with wine, the better.  

      • Research in model solutions showed that 50% of the seed tannins were extracted during 10 day maceration while 80% were extracted during 30 day maceration. Extended maceration also leads to a decrease in anthocyanins, which means loss of color (Casassa and Harbertson 2016). Sensory analysis for this study showed sensory profiles of wines with extended maceration had decreased fruitiness, higher astringency and higher vegetal aromas than wines with less maceration (Casassa and Harbertson 2016).

    • Consider delestage and/or seed removal. If you do delestage, make sure to be gentle when you rack back onto the cap. This racking will allow better dissipation of color and a good oxygenation for color fixation.  Seed removal along with delestage further limits exposure to underripe tannins.  If you have a way to remove seeds during pumpovers (through a mesh screen, for example), remove as many as possible. (Zoecklein #78)

    • Gentle cap management after mid-fermentation limits over-extraction of harsh tannins and prevents loss of fruit aromas and flavors (Zoecklein #81).

  • Pressing

    • Roujou de Boubee (2002) found higher IBMP levels in press wines, indicating a portion of IBMP remains in the skins and is released as pressing. Press gently and keep press fractions separate. Much of what you don’t want is in the skins  and will come out with the press fractions.  Fining agents can be used to remove phenolics from press fractions later, without fining the whole lot.

  • Racking

    • Allow gross lees to settle after pressing for 24 hour, then rack.  Rack again after 2 days (Zoecklein #78, Scottlabs).  Methoxypyrazine will bind to lees and settle out, so the more lees you remove, the less MP you are taking to barrel (Chauffour 2017).  Also, oxygen during racking is helpful for reducing reduced sulfur compounds and helping tannin polymerization (to reduce astringency).

After alcoholic and malolactic fermentation are complete, there are additional interventions that can be considered in the cellar. These include micro-oxygenation (Zoecklein #114, Mozzon et al 2016), several additives and wood exposure. These considerations will be explored in subsequent newsletters.



References

Bogart, K, and L. Bisson (2006). Persisten e of vegetal character in wine grapes and wine. Practical Winery and Vineyard Journal (March/April)

Casassa, F and J Harbertson (2016). Studying the relationship between seed maturity, length of maceration and ethanol amount on Merlot wines. Wines and Vines (Sept)

Chauffour, Eglantine (2017, Nov 9). “Tools to manage green character in the winery”, Virginia Wineries Assciation Technical Meeting, Wintergreen Resort, Virginia.

Gardiner, Denise (2014). Getting Ready for Harvest Part 3: Reducing “Green” Flavors in Red Wines, Wine and Grape U, Pennsylvania State University.

Pickering, G et al (2008). Yeast strain affects 3-isopropyl-2-methoxypyrazine concentration and sensory profile in Cabernet Sauvignon wine. Aust J Grape and Wine Res 14(3):230 - 237

Roujou de Boubee, D, et al (2002). Location of 2-methyoxy-3-isobutylpyrazine in Cabernet Sauvignon grape bunches and its extractability during vilification. AJEV 53:1: 1-5

Scottlabs. Optimizing wine from under-ripe red grapes. Retrieved Sept 16, 2018

Sherman, E et al (2018) Impact of Grape Maturity and Ethanol Concentration on Sensory Properties of Washington State Merlot Wines. ASEV 68: 344-356

Zoecklein, Bruce, Enology Notes, Wine/Enology Grape Chemistry Group, Virginia Tech. 

#61 Red wine Phenolic Management

#78 Short Vatting

#81 Maximizing Aroma/Flavor and Structure in the 2003 Red Wines

#94 Herbaceous Character in Red Wines

#114 Heraceous Character in Red Wines