Mouton Noir

_{My sunflower(s).}

I've been growing sunflowers on my balcony, which has been both rewarding and brought unexpected joy to my life. I also noticed that a) these plants are seriously thirsty, and b) there is a definitive positive correlation between water supply and growth.

Now that I'm entering a world where irrigation is not allowed, I got curious about the old saying that vines that struggle produce better grapes.

I found the following four papers on the relationship between water deficit and berry compositions. _{Please note that the research was conducted in the US (and Greece) with Cabernet Sauvignon (and chardonnay).}

Research Papers

Paper #1

_{(Click here for the paper.)}

Objective: Investigate the effects of water stress on Cabernet Sauvignon grapevine at different phenological stages.

Key Insights:

• Water stress impacts berry growth, CO2 exchange rate, and leaf area.
  • Explanined: These are ways to describe how grapevines are growing. Less water can slow down how quickly the grapes grow, change how the plants breathe (CO2 exchange), and affect the size and number of leaves. These changes can alter how the grapes develop
• Water stress improved berry composition when applied in a specific sequence (no stress from anthesis to fruit set, mild stress from fruit set to veraison, moderate to severe stress post veraison).
  • Explanined: These are different stages of grape development:
    • Anthesis to Fruit Set: When flowers turn into tiny grapes.
    • Fruit Set to Veraison: When those tiny grapes grow and mature.
    • Veraison to Harvest: When the grapes change colour and get ready to be picked.
• The relationship between berry composition and vine water status varied depending on the stage and parameter measured.

Conclusion in plain English: Watering the grapevines less at specific times can make the grapes better for winemaking. If you water them fully as they start to grow, then cut back a little, then cut back even more as they ripen, it can make the grapes taste and look better in the wine. But the exact effect can vary depending on the timing and what you're trying to achieve with the wine.

Paper #2

_{(Click here for the paper.)}

Objective: Analyse the global effects of water deficit on the metabolic pathways of Cabernet Sauvignon and Chardonnay grapes.

Key Insights:

• Water deficit affected various metabolic pathways differently depending on the grape cultivar.
• In Cabernet Sauvignon, water deficit increased anthocyanin concentrations and activated glutamate and proline biosynthesis.
  • Explanined:
    • Anthocyanins help to give red wines their colour. Less water makes the colour of Cabernet Sauvignon deeper or more intense.
    • Activated Glutamate and Proline Biosynthesis in Cabernet in the grape can affect the taste, making it richer or more complex.
• In Chardonnay, it increased concentrations of antheraxanthin, flavonols, and aroma volatiles.
  • Explanined: These are compounds that can change the colour, flavour, and smell of Chardonnay. Less water might make the wine more aromatic and flavorful
• Water deficit also doubled ABA concentrations in Cabernet Sauvignon but decreased ABA in Chardonnay, affecting berry flavour and quality characteristics.
  • Explanined: ABA is a compound that affects how the grapes ripen. More of it in Cabernet Sauvignon and less in Chardonnay due to water deficit can lead to differences in flavour and quality.

Here's an interesting graph chart from the paper:

The effects of water deficit on various grape vine and berry parameters over time.

_{A) stem water potential, B) berry diameter, C) berry soluble solids, D) berry titratable acidity.}

_{Vertical magenta and green dotted lines mark the boundaries for véraison for Cabernet Sauvignon and Chardonnay, respectively. Arrows mark sampling dates for molecular analyses.}

_{Symbols represent means ± SE; n = 6. CH = Chardonnay, CS = Cabernet Sauvignon, WW = well watered, WD = water deficit.}

Conclusion in plain English: Giving less water to grapevines can affect different types of grapes in various ways. For Cabernet Sauvignon (a red wine grape), less water might make the colour richer and the taste more complex. For Chardonnay (a white wine grape), it might lead to more aroma and flavour. It's not a one-size-fits-all approach; the effects depend on the type of grape and what the winemaker wants to achieve. By managing the water carefully, winemakers can bring out specific qualities in different wines.

Paper #3

_{(Click here for the paper.)}

Objective: Investigate the effects of vineyard location and water status on the grape and wine composition of Agiorgitiko in southern Greece.

Key Insights:

• Water deficit accelerated sugar accumulation, malic acid breakdown and beneficially affected the concentration of anthocyanins and total phenolics in berry skins.
  • Explanined:
    • Less water causes the grapes to have more sugar more quickly. More sugar can mean more potential alcohol and a sweeter taste in the final wine.
    • Malic acid is one of the acids in grapes that give the wine its tart taste. Less water leads to less malic acid, so the wine might taste less sharp or tangy.
    • Anthocyanins are the compounds that give red wine its colour, and phenolics can influence the taste and mouthfeel. Less water can lead to more of these, meaning a deeper colour and possibly a richer taste.
• Water stress increased glycoconjugates of aromatic components, and wines from stressed vineyards were preferred in tasting trials.
  • Explanined: This refers to changes in the aroma compounds in the grapes. Less water seems to make certain aromas in the wine more intense or noticeable.

Conclusion in plain English: Cutting back on the water that grapevines get (water deficit) can make the grapes ripen in a way that often produces better wine. The grapes get sweeter faster, there's less of a sharp, tart taste, the color may be deeper, and some aromas may be more intense. People even preferred these wines in taste tests. It's a technique that can be used to bring out certain desirable qualities in wine.

Paper #4

_{(Click here for the paper.)}

Objective: Understand the effects of early (ED) and late (LD) season water deficits on Vitis vinifera “Cabernet Sauvignon” gene expression and flavonoid biosynthesis.

Key Insights:

• Both ED and LD increased anthocyanin accumulation after veraison by enhancing the expression of genes controlling anthocyanin biosynthesis.
  • Explanined: Anthocyanin Accumulation after Veraison: Anthocyanins are pigments that give red wine its colour. Veraison is the stage of grape ripening where the grapes soften and begin to gain colour. Increasing anthocyanin accumulation means the grapes will have a deeper colour.
• ED accelerated sugar accumulation and the onset of anthocyanin synthesis. Increases in anthocyanins were predominantly in the 3'4'5'-hydroxylated forms, with limited effects on other flavonols or proanthocyanidins.
  • Explanined:
    • Giving less water early on makes the grapes gain sugar faster and start producing colour earlier. This can result in wines with a richer taste and deeper colour.
    • 3'4'5'-hydroxylated refers to specific types of anthocyanins that affect colour. It means the particular way the colour changes due to water deficit leads to a specific shade or intensity of red.
    • Flavonols and proanthocyanidins are other compounds in grapes that affect flavour and colour, but they are not influenced much by water deficit in this context.

Conclusion in plain English: When grapevines experience certain conditions like water stress, it changes the types of colour compounds (anthocyanins) in the grapes. This means the grapes can develop a richer and more complex colour. The changes mostly happen in one specific type of these colour compounds, without much effect on other related compounds (flavonols or proanthocyanidins) that might affect things like taste or mouthfeel.

When rain might be good or bad

If we cannot irrigate, the only source of water is from the sky.

When Rain is Good:

• Anthesis to Fruit Set: Adequate rainfall during this early stage can support berry growth and the development of anthocyanins and polyphenols, which are essential for wine quality.
• Before Veraison: Mild water stress has been found to be beneficial, so a balance between rain and dry periods might be optimal during this phase to induce mild stress conditions.
• During Drought Years or in Naturally Dry Regions: Rain can be beneficial to prevent excessive water stress that might otherwise negatively impact vine growth, CO2 exchange rate, and leaf area.

When Rain Might be Bad:

• Fruit Set to Veraison: Excessive rainfall leading to a lack of water stress during this stage might hinder the beneficial effects observed with mild water stress on berry composition.
• Veraison to Harvest: Rain near or during harvest might dilute berry composition and negatively affect the concentration of sugars and other flavour compounds. It could also promote disease, affecting grape quality.
• Post-harvest: Excessive rain after harvest could lead to issues related to vine recovery, nutrient leaching, and preparation for the next growing season.

Conclusion

These papers show that water – how much or little of it the grapevines get – plays a big role in the taste, colour, and smell of the grapes. By understanding this, farmers and winemakers can grow grapes that make better wine. Different grapes respond differently to water, so the right approach depends on the type of grape and what kind of wine is being made. In places where farmers can't water their vines, these insights can still help them use the natural rain to their advantage.