Tannins

Tannin management in the vineyard

Tannins are a key component of grape composition and play an important role in the quality, style and longevity of many wines. For grape growers and viticulturists, understanding the factors that influence tannin development can help inform decisions about vineyard management, site selection, canopy design, vine balance and harvest timing. While tannin outcomes are ultimately influenced by winemaking, the vineyard establishes much of the foundation for tannin concentration, composition and extractability.

Why tannins matter

Tannins are naturally occurring polyphenolic compounds found in grape skins, seeds and, to a lesser extent, stems. They contribute bitterness, astringency, mouthfeel and structural complexity in wine, while also helping to stabilise colour in red wines through interactions with anthocyanins.

For growers, tannins are more than a winemaking consideration. Tannin levels and composition can influence fruit value, wine style potential and a vineyard's ability to consistently meet winery specifications. In premium red wine production, tannin quality is often as important as sugar levels, acidity and flavour development.

Understanding tannin development is particularly important as wine producers increasingly focus on texture, balance and longevity rather than simply colour intensity or alcohol levels. Vineyard decisions that affect vine growth, bunch exposure and fruit maturity can all influence tannin outcomes.

What tannins do in the grapevine

Tannins form part of the vine's natural defence system. They help protect grapes against micro-organisms and herbivores by binding proteins and creating physical barriers when plant tissues are damaged. Their naturally bitter and astringent character also discourages pests from feeding on leaves and fruit.

In grapes, condensed tannins are concentrated primarily in the skins and seeds. During berry development, tannins accumulate before veraison and continue to change as berries mature. However, research shows that tannin development patterns can vary significantly between regions, seasons and grape varieties.

The challenge: grape tannin does not always equal wine tannin

One of the most important insights for growers is that higher grape tannin levels do not automatically translate into higher wine tannin levels. Research has shown that substantial amounts of tannin become associated with grape cell walls during berry development. During fermentation, these cell walls can bind tannins rather than release them into the wine, reducing extraction efficiency.

This helps explain why vineyards with apparently high tannin fruit do not always produce wines with the expected tannin concentration or mouthfeel. It also highlights the importance of close collaboration between viticulture and winemaking teams when assessing fruit quality targets.

What drives tannin variation?

Variety matters

Different grape varieties naturally produce different tannin concentrations and tannin structures. Research has shown significant variation between cultivars, with differences not only in total tannin levels but also in polymer length and composition. Interestingly, some table grape varieties have been found to contain higher skin tannin concentrations than certain winegrape varieties.

Practical implication: Benchmark tannin expectations against your specific variety rather than relying on general assumptions about "high" or "low" tannin cultivars.

Site and season effects

Seasonal conditions are among the largest drivers of tannin variability. Temperature, sunlight, rainfall and vine water status during berry development all influence tannin accumulation. Research has demonstrated substantial year-to-year differences, often exceeding variation observed between regions.

Even within a single vineyard block, tannin levels can vary considerably from one area to another. Studies identified consistent zones of higher and lower tannin concentration across multiple seasons, indicating that underlying site characteristics can significantly influence outcomes.

Practical implication: Consider spatial vineyard monitoring and precision viticulture approaches to identify areas of consistent fruit quality variation. Management zones may offer opportunities for differential management or selective harvesting.

Vine vigour is a critical factor

Among the vineyard factors studied, vine vigour emerged as one of the strongest and most consistent drivers of tannin variability. Higher vigour vines were generally associated with lower tannin concentrations, while lower vigour vines tended to produce fruit with higher tannin levels.

Practical implication: Maintaining balanced vine growth should be a key objective. Excessive canopy growth can reduce fruit composition outcomes, including tannin concentration, whereas moderate vine balance may help optimise fruit quality.

Bunch exposure and canopy management

Canopy management has long been used to influence colour development, but its effects on tannins are less predictable. Research found that some varieties responded positively to increased bunch exposure, while others showed little change or even opposite responses.

Practical implication: Avoid assuming that leaf removal or increased fruit exposure will improve tannin outcomes in every vineyard. Responses are variety-dependent and should be evaluated locally through observation and measurement.

Rootstock selection

Research indicates rootstocks may influence tannin concentration, although current evidence remains limited and sometimes inconsistent. Some studies reported differences between rootstock combinations in Shiraz, Merlot and Pinot Noir.

Practical implication: When establishing new vineyards, rootstock selection should be considered alongside water management, vigour control and fruit quality objectives, but tannin outcomes alone should not drive rootstock decisions.

Irrigation management

Irrigation and deficit irrigation strategies generally do not appear to directly increase grape tannin concentration. Reported effects are largely due to changes in berry size, which can concentrate tannins through a higher skin-to-pulp ratio.

Practical implication: Water management remains important for overall vine balance and fruit quality, but growers should not expect irrigation changes alone to dramatically alter tannin accumulation.

Key vineyard management considerations

To support consistent tannin development and wine quality outcomes:

• Maintain balanced vine vigour and avoid excessive canopy growth.
• Monitor within-vineyard variability and understand site-specific patterns.
• Use canopy management practices based on local evidence and varietal response.
• Consider tannin potential alongside other fruit quality measures when determining harvest timing.
• Work closely with winemakers to understand tannin requirements for target wine styles.
• Recognise that tannin extractability can be as important as tannin concentration.

What we know and what we still need to understand

Research clearly shows that all grapes contain tannins, that substantial variation exists between sites, seasons and varieties, and that vine vigour is one of the most important factors affecting tannin levels. However, there is still no clear definition of the ideal tannin composition for specific wine styles, nor a complete understanding of how vineyard practices influence wine tannin perception.

For growers, the key takeaway is that tannin management should be viewed as part of an integrated vineyard quality strategy. Rather than focusing solely on increasing tannin levels, the goal should be producing balanced fruit with the greatest potential to express variety, site and intended wine style.