The Harvest Season Series #1: How Grape Picking Affects Wine Quality

As we head into autumn in Europe, we find ourselves in the middle of the period of grape harvests, the most crucial period for winemakers across the northern hemisphere. The quality of the harvested grapes plays a vital role in determining the flavour, aroma, structure, and overall quality of the wines in the bottles that we get to enjoy.

While many factors influence the characteristics of a wine, from soil type to climate, arguably the most critical is choosing the perfect moment and method to harvest the grapes. The timing, method, and conditions of grape picking can significantly affect wine quality, making the harvest season one of the most important events in a winemaker’s calendar.

The All-Important Timing of the Harvest

One of the most critical decisions winemakers face is determining the ideal time to harvest the grapes. Picking too early or too late can have significant consequences on the final wine. Why? Because grape ripeness is a delicate balance between sugar, acid, and tannin development. This balance is key to creating well-structured wines.

During the growing season, grapes go through various stages of development. Initially, they are high in acidity and low in sugar. As they ripen, the sugar content increases while acidity levels decrease. This can be at different rates depending on the grape variety in question. Viognier, for example, is notable for the speed at which acidity can drop, and harvest timing is crucial in the quality of wines from this varietal.

At the same time, phenolic compounds, such as tannins and colour pigments, mature, influencing the final wine’s texture, colour, and ageing potential. Winemakers must monitor the grapes carefully to determine the precise moment when these elements reach their optimal levels.

Picking moment and the resulting wine

Early Harvest

Grapes picked early will have higher acidity and lower sugar levels, leading to wines that are crisp, fresh, and light in the body. These wines often have more herbaceous and tart fruit characteristics. While early picking is ideal for sparkling wines, where high acidity is desired, it can result in overly acidic and thin still wines if mistimed.

As winemakers look to produce better quality low-alcohol wines for market demand, earlier harvests (hence lower levels of fermentable sugars) is one method being explored.

Late Harvest

Grapes left on the vine longer will continue to accumulate sugar, and the resulting wines tend to be fuller-bodied with higher alcohol content. However, delaying the harvest too long can lead to overripe fruit, resulting in wines that are overly sweet, jammy, or lacking structure. Late harvests can also increase the risk of diseases like botrytis (noble rot), which may be desirable for dessert wines but detrimental for dry wines.

Late-harvest wines are well suited to high-acid grape varieties such as Chenin Blanc in the Loire Valley and Furmint in Hungary.

The wine style matters!

The decision of when to harvest often depends on the style of wine the winemaker is aiming for, the grape variety, and the region’s climate. For instance, in cooler climates like Burgundy in France or the Mosel in the north of Germany, winemakers may wait for longer ripening periods to achieve sufficient sugar levels, while in warmer regions like Napa Valley, they may harvest earlier to preserve acidity.

Impact of Weather on Harvest Timing

Weather conditions leading up to and during the harvest season can greatly affect grape quality and the timing of the pick. A winemaker may have carefully planned the perfect harvest date, but unexpected weather events can force a change in strategy.

Rain

Rain during harvest can dilute the sugar concentration in the grapes and increase the risk of mould and rot. In such cases, winemakers may choose to harvest earlier than planned to avoid potential crop damage, even if the grapes haven’t fully ripened.

Frost

In cooler regions, the threat of early autumn frost can damage the grapes or stop the ripening process altogether, forcing winemakers to pick the grapes prematurely.

Heatwaves

Excessive heat near harvest time can cause grapes to ripen too quickly, leading to imbalances in sugar and acidity. Grapes picked during or after a heatwave may result in wines that are overly alcoholic or lack freshness.

Weather unpredictability makes grape picking a high-stakes gamble for winemakers. It’s not just a question of optimal ripeness but also risk management, balancing the desire for perfect maturity with the need to protect the grapes from damage. Many wine associations around the world, such as the CIVB in Bordeaux or the Consejo Regulador of Rioja, produce weather charts for their members to keep them informed of forthcoming weather patterns, as well as offer advice on picking dates.

Oftentimes, we tend to overlook these lesser-known or regional grape varieties under the shadow of popular varietals. In the following section, we have selected five lesser-known, some almost forgotten, grape varietals that produce intriguing wines beyond the mainstream.

Man or Machine?

Another critical decision during the harvest is the method of picking — whether to harvest the grapes by hand or use machines. Both methods have advantages and drawbacks, and each has a significant impact on wine quality.

Manual Harvesting

Handpicking grapes is the traditional method of harvesting and is favoured for its precision and care. Workers carefully select only the ripest clusters, avoiding damaged or diseased fruit. This method allows for better quality control and is often in the rules for high-end wines, where winemakers want to ensure that only the best grapes go into the bottle. It is essential for vineyards located on steep slopes or those with irregular terrain, like those found in regions such as the Douro Valley.

The downside of manual harvesting is that it is labour-intensive and expensive, contributing to the higher price of wines made from handpicked grapes.

Mechanical Harvesting

The use of machines to shake the vines and collect grapes quickly and efficiently has come leaps and bounds in recent decades. For wines where large-scale production is necessary, such as in some New World regions, mechanical harvesting is often the only viable option.

While this method is faster and more cost-effective, it lacks the precision of handpicking. Machines do not discriminate between ripe and unripe fruit, and they may also pick up leaves, stems, and other debris along with the grapes. The resultant wines may require more intervention during the winemaking process, such as additional sorting or filtering, to ensure the final product is of good quality.

Grape Sorting and Its Impact on Wine Quality

Another crucial step that impacts wine quality is grape sorting, ensuring that only the best grapes make it into the fermentation tanks, whilst removing leaves, stems, and other debris that may have been picked up during the harvest.

Manual Sorting

Many high-end wineries employ manual sorting tables where workers visually inspect and remove any undesirable grapes or debris. Although labour-intensive, it allows for greater precision and results in higher-quality wine, as only the best fruit is used.

Optical Sorting

In recent years, advanced technology like optical sorting machines (developed by the pea and nut industries) has gained popularity. These machines use cameras and sensors to sort grapes based on colour, size, and shape, allowing for extremely precise sorting at a faster pace than manual methods.

The Role of Terroir and Vineyard Practices

Ultimately, the harvest is a reflection of the vineyard’s terroir and the skill of the farmer in managing the vines throughout the growing season. Even the most carefully planned harvest will fail to produce high-quality wine if the vineyard has been poorly managed, or the terroir is not suitable for the grape variety being grown.

This Blog post is written by Mike Turner
Freelance wine writer, presenter and judge

Mike is a regular contributor for The Buyer magazine and is a certified educator and ambassador for Bordeaux, Rioja, Ribera Del Duero, Barolo and Barbaresco, running trade and consumer events across the UK from his base in the East Midlands.