¿Is it possible to reduce berry sugar content while keeping acidity and phenolic structure in warm climates? Advanced Viticultural Practices

2. Delaying the grapevine cycle

2.1. Delayed pruning

Delayed pruning leverages apical dominance to postpone budbreak and ripening. When applied after budburst or even at flowering, it can delay harvest by up to two months. This technique increases acidity (up to +35%) and phenolic content (up to +34%), while reducing yield significantly (up to –75%) (Martínez-Moreno et al., 2019; Petrie et al. 2017, Zheng et al. 2017 and Pallioti et al. 2014).

The timing is critical: “Too early does not affect berry composition; too late (flowering) can devastate harvest.” Despite yield losses, delayed pruning is effective in mitigating the decoupling of technological and phenolic maturity in warm climates.
It is particularly useful in Mediterranean regions where high temperatures during ripening reduce acidity and color in grapes.

2.2. Crop-load increase

Increasing the crop load reduces the leaf area-to-yield (LA/Y) ratio, delaying ripening and enhancing acidity. High crop loads can increase yield by 16–66% and reduce °Brix by 10–15% or delay the ripening and consequently, the harvest date (Martínez de Toda, 2019a; de la Fuente et al., 2016 and Pallioti et al. 2014). This LA/Y ratio is generally balanced around 1 m2/kg, with values below 0.8 m2/kg slowing berry maturity. This technique is effective but may require careful water management in semiarid regions.

2.3. Crop forcing

Crop forcing involves hedging shoots and removing leaves and clusters to induce a second budburst. It can delay ripening by 30–65 days, increase acidity (up to +60%), and phenolic content (up to +48%), while reducing °Brix and pH.

However, it also causes significant yield losses (34 –92%) with high variability. This technique is promising for restoring the anthocyanin/sugar balance disrupted by warming, but must be applied with expertise. The timing of forcing is critical, with post-anthesis applications yielding better results. Crop forcing after fruit set shifted fruit ripening and, consequently, harvest time to the October to early November period (Cabral et al., 2023; Oliver-Manera et al., 2023; Lavado et al., 2019; Martinez De Toda, 2019a; Martínez-Moreno et al., 2019). Crop forcing can also reduce water stress during ripening and improve wine color and stability.

2.4. Double harvest

Double harvest involves collecting grapes at two different times: early for high acidity and low sugar, and late for phenolic maturity. This strategy enables the production of wines with balanced alcohol and acidity, especially in warm climates. It is particularly useful for cultivars like Tempranillo (Martínez de Toda, 2019), where phenolic and technological maturity are often decoupled. By combining early and late harvest fractions, winemakers can achieve better balance in the final wine. Another relevant possibility is directly blending the two produced wines because all grapes are grown in the same vineyard, with the same variety, and there is no problem with current DO regulations. Today, modern enological technologies can help to keep the must/grapes unaltered until the fermentation process, or even wines. This technique also offers flexibility in harvest scheduling and can mitigate the risks of over-ripening and sunburn.

3. Modifying leaf area‑to‑yield ratio

3.1. Canopy management

Trimming and late leaf removal are effective tools for modulating LA/Y and delaying ripening. Trimming after berry set can delay ripening by 14–23 days and increase anthocyanins (Santesteban et al, 2017 and Martínez de Toda, 2019a).

Late leaf removal slows sugar accumulation and improves acidity without increasing sunburn risk, especially when basal leaves are preserved (Palliotti et al., 2013 and Buesa et al., 216).

These practices help manage the microclimate around the clusters, reducing heat stress and improving phenolic development. Canopy management is a flexible and cost-effective strategy for adapting to climate change.

Applying minimal pruning reduces also the leaf area-to-yield (LA/Y) ratio, delaying ripening and enhancing acidity. Minimal pruning, designed for mechanization, increases cluster number and yield while reducing berry weight and delaying ripening.

Minimal pruning also reduces labor costs and can improve sustainability (Martínez de Toda, 2019b).

This technique is effective but may require careful water management in semiarid regions.

3.2. Sunlight exposure Training systems

Row orientation and canopy structure influence sunlight exposure and microclimate. Orientations like NW–SE can reduce afternoon heat stress, improving water use efficiency and berry quality.

Sprawl systems increase shading, reduce sunburn, and enhance anthocyanin content, making them suitable for hot climates.
Open training systems can also improve air circulation and reduce disease pressure. Adjusting trellis height and shoot positioning can further optimize light interception and temperature regulation, contributing to improved grape composition.

Therefore, a better exposition (less light intensity, cooling effect that reduces grape transpiration, etc.) marked low stem water potentials during the berry maturity process, which increases the WUE (around 10%) and, therefore, was relevant for the berry weight (7-12%), number of clusters, and yield (up to 18%) increments, without affecting berry composition (pH, °Brix), only a notable increase (18%) in total polyphenol fraction and in some cases, keeping more acidity (12%) in the berry (de la Fuente et al., 2016; Buesa et al., 2020 and de la Fuente et al., 2023).

3.3. Yield management

The main tool applied is crop load management (see 2.2. point), because thinning clusters at a particular moment (before veraison) usually implies a high cost to the plant (in photoasimilate quantity), but it is useful to regulate the maturity in some fruitful varieties (more than 2 clusters per shoot).

4. Other long-term or mid‑term strategies

4.1. Soil management: cover crops and mulching

Cover crops and mulching improve soil structure and microclimate. Cover crops reduce canopy temperature and erosion but may increase water demand. Mulching conserves soil moisture and buffers temperature, though it may affect berry composition.

Both practices support sustainable viticulture under water-limited conditions. They also enhance soil biodiversity and organic matter content, contributing to long-term vineyard health. Selection of appropriate species and timing of management are key to maximising benefits (de la Fuente et al., 2026).

In addition, cover crops have relevant effects on grapevine vegetative development, if both crops are growing at the same time due to resource competition.

4.2. Irrigation considerations

Irrigation strategies must balance water use with quality goals. Deficit irrigation can help maintain acidity and control pH, while excessive irrigation may dilute berry compounds. Integration with canopy and soil management is essential for optimizing grape composition under climate stress. Sustainable irrigation practices, such as regulated deficit irrigation (RDI), can improve water use efficiency and maintain grape quality. Monitoring vine water status and soil moisture is essential for precise irrigation scheduling. In general, some authors report that overoptimal irrigation can have a detrimental effect on sugar content and lead to delayed ripening, increased acidity, reduced berry color intensity, and a smaller yield (de la Fuente et al., 2026).

4.3. Variety or rootstock selection.

Grapevine varieties have traditionally been classified also as early-, mid-, or late‑season ripening, a system based on harvest date or heat accumulation rather than the true ripening process (from veraison to a given sugar point or ºBrix degree). This approach is biased, as it reflects differences across the whole phenological cycle and is not related to maturity or development ratios from fruitset to veraison or ripening. Studies showed that genotypic variability in sugar ripeness decreases when sugars are expressed on thermal scales from veraison onward (Duchêne et al., 2012). The shift from active sugar accumulation to passive concentration is also genotype‑dependent (Deloire, 2011, Shahood et al., 2020), influenced by a maximum berry size and the possible weight loss, being some varieties faster in sugar accumulation (Tempranillo) than others with moderate or mid-faster rates (Garnacha or Syrah) or even, slow varieties (Bobal). Natural variation remains essential for breeding programs, and recent screenings of minor or disease‑resistant varieties have identified candidates with better sugar–acidity balance for warmer climates (Frioni et al. 2023). However, poor attention has been given to genotypic variation in veraison timing and sugar accumulation rate, despite evidence that ripening speed varies genetically.

Advances in grapevine omics have clarified developmental transitions, yet genes controlling sugar accumulation remain poorly understood. Recently, a ripening‑speed locus introgressed from Vitis riparia was identified, reducing daily TSS accumulation after veraison without altering ripening onset (Falginella et al., 2025).

Conclusions

There is no unique solution for improving red wine quality under climate change, as each vineyard requires tailored decisions. Several practices, however, effectively delay ripening but also have positive or negative effects. Late pruning increases acidity and phenolics but reduces yield. Increasing crop load boosts production and lowers Brix at a given date. Minimal pruning raises cluster number and yield while improving acidity and phenolic content through delayed ripening. Crop forcing can postpone harvest by one to two months and enhance acidity and phenolics, but with severe yield losses. Double harvest offers a simple way to obtain musts with high acidity and fully ripe skins. Adjusting training systems, trimming, and late leaf removal helps modulate sunlight exposure, reduce the LA/Y ratio, and delay ripening with limited impact on other grape components. Other long or mid-term strategies (cover crops, soil management, irrigation techniques, varietal selection) can be useful too but imply more time or resources to their implementation.