Harvesting is Delicate

Does the beauty of machine harvesting produce beautiful wines?

Mechanical harvesting became increasingly common in the Old World around 40 years ago. Its primary advantage is efficiency, reducing manual labour in the vineyard by approximately 30–40%.

Harvest is a delicate, time-sensitive operation in which hostile weather conditions and sudden disease pressure can quickly become costly problems. When yields per metre are sufficient, machine harvesting can be significantly cheaper, far faster, and often more environmentally friendly. In most cases, only two operators are required in the vineyard to manage both harvesting and transport to the winery.

Mechanical harvesting also allows wineries to operate equipment closer to full capacity, making processing faster and cheaper while saving water, time, and energy associated with cleaning. It is common to process two to three times more fruit than with hand harvesting. For example, 18 tonnes can be processed by three people using a three-tonne press in a 17-hour shift. Additionally, leaving stems on the vine—typically 3–7% of the grape weight and over 30% of the volume—simplifies marc management.

What about quality—for still and sparkling wines?

To simplify the discussion, let us consider a single-estate scenario in which the vineyard surrounds the winery. With appropriate logistics, however, grapes can also travel several miles, or be de-juiced and settled on site before transport.

The key point is this: once berries are detached from the stem, some juice is released, initiating both maceration and oxidative processes. Is this beneficial or detrimental? The answer depends entirely on the intended outcome.

Below are three possible approaches, explored within a UK context and focused on oxidation and maceration (extraction):

• Oxidative

• Balanced

• Reductive

Oxidative approach

In an oxidative approach, no protective measures against oxidation or microbial activity are used—such as SO₂, tannins, ascorbic acid, inert gas, or chitosan. This method can be appropriate for non-aromatic wines where shelf life and ageing potential are priorities, such as sparkling wine bases.

In this scenario, certain compounds are deliberately oxidised while new ones are formed. Although this may appear counterintuitive, oxidation at the juice stage removes compounds—primarily phenolics and free primary aromas—that would otherwise continue to oxidise later. As a result, the finished wine can display improved stability, ageing capacity, and potential for tertiary aroma development.

The degree of oxidation can be carefully managed and is particularly effective when handling press fractions, helping to reduce colour and tannin levels in the final wine.

Balanced approach

The balanced approach offers moderate protection while providing the greatest flexibility for creating diverse blending components, particularly for both still and sparkling wines. It allows batch-by-batch adaptation, and individual press fractions can be treated differently according to taste and stylistic goals.

This approach supports sustained fruit expression, solid ageing potential, and the development of secondary and tertiary aromas.

Reductive approach

The reductive approach aims to preserve primary aromas, retain a certain phenolic structure, and deliver moderate shelf life (red wines being a separate discussion). Wines made reductively require high levels of protection throughout their entire life cycle.

This strategy is particularly suitable for aromatic still wines and certain sparkling styles, such as Charmat-method wines.

Managing maceration and oxidation

In all cases, maceration and oxidation must be managed in line with the target style. For example:

• Longer, balanced macerations are often suitable for rosé wines and aromatic white varieties with precursor compounds.

• Shorter macerations are preferable for non-aromatic whites.

• Very rapid de-juicing is critical for classic sparkling bases, where timing from harvest to press is essential.

In many situations, phenolic levels can be reduced with positive effects by encouraging controlled oxidation at the juice stage and/or by using fining agents such as PVPP or proteins at different stages.

Conclusion

In summary, everything depends on intent. Yes—machine-harvested grapes can produce high-quality wines of many styles, provided that the appropriate criteria, techniques, and equipment are applied. The same principles can also be applied to hand-harvested fruit, depending on the desired outcome.