As wineries across the globe are in constant preparation to assess their crop and carefully predict grape maturity levels, wine-lovers everywhere are stocking their cellars with wines from years prior. The long production timeline behind any bottle of wine shows just how much care goes into crafting every single glassful; and each year, winemakers face a challenging decision that, as non-professionals, can be difficult to understand.

Lagoa-based winery Quinta dos Vales is known to offer wine-lovers the opportunity to authentically become wine-makers, as part of their project The Winemaker Experience, which allows participants an insight into what the world of wine-making is truly like. One of the questions to solve amidst the harvesting season, is when growers are forced to decide on whether they should pick the grapes. It seems simple enough—grapes are as easy to harvest as any other fruit, right? Well, believe it or not, harvesting grapes for wine is not as simple as picking a strawberry to pair with tomorrow morning’s breakfast.

As winemakers tend to grapes, they devise specific schemes for optimizing each vintage. The fruit develops into what is ultimately the foundation of our favourite wines, with indescribable flavours that are nothing less than a treat to the senses. Grapes themselves continuously develop while hanging on the vines. Picking them too early can deprive Mother Nature of her most cherished job: refining the colour, flavour, aromas, acidity and sugar content.

So, how do winemakers confirm that a grape’s maturity has been reached before picking it?

Predicting the Grapes’ Maturity Levels

For their cellar-management winemakers use historical information to predict when grapes will be ready for harvest. Using historical data of the proper harvest times from years prior, the team will plan weeks ahead of time which variety of grapes will be ready for harvest at what point. But at the end of the day, this is merely a prediction; it is Mother Nature who decides when grapes reach their full potential. It’s not uncommon for grapes to have a mind of their own. And, although they predict ahead of time, winemakers typically come to a crossroads when harvesting.

In recent years, people have preferred wines with lower alcohol levels. The trend has allowed especially white wines and rosés to make gorgeous pairs with meals and make lovely companions for hanging out and relaxing on a quiet afternoon.

Moving into this year’s harvest, some winemakers, like the ones of Quinta dos Vales, are planning to take a different approach for some selected varieties. Rather than prioritising moderate alcohol levels, some varieties will be left slightly longer in the vineyards. The additional time will allow them to refine their taste, texture, and quality to come as close as possible to a full phenolic maturation.

All in all, these selected wines are expected to have an increased longevity, a full and richer body, a slightly mellow taste, deeper colours, and a long lasting mouthfeel.

The final steps before the harvest - Understanding the grape compounds

While it may sound like a simple process, winemakers actually need to run a series of tests in order to better understand the chemical makeup of the grapes as they near maturity.

As grapes develop on the vine, acidity levels will decrease while sugar content increases. Flavour molecules emerge as the grapes reach ripeness; the single grape converts itself into a kind of power-plant, this is what mainly leads to the phenolic maturity. On a chemical level testing phenolic maturity includes looking at how much of each chemical compound is present in the grapes, the compound's structure, and how easily water dissolves these compounds (extractability). Furthermore, as phenol matures in grapes, bitterness will transform to a soft, round taste. So, for example, a simple field test for a winemaker, when biting into a grape if a bitter flavour dominates the palate, a grape has not yet reached its phenolic ripeness.

But, it isn’t enough to merely check how technologically mature the grapes are based on their sugar and acid contents. Winemakers must also look at the anthocyanin that develops in grapes, a pigmented compound that is the principal source that gives grapes their deep colour and wine-lovers their health-related benefits. Analysing this phenolic maturity is not as simple as plucking a few grapes from a vine and stomping on them to release their juices.

Amongst the historical data, winemakers must therefore combine two criteria to determine the ideal date for harvesting, implementing both objective and subjective analyses—a perfect blend between a grape’s technical data and the winemaker’s instincts.

Technical Analysis

For winemakers, the technical analysis is considered the easy part. Winemakers measure three things during the technical analysis: density, pH, and acids.

Sugar content helps define the alcohol content, making it an essential piece of the wine-making puzzle. Nonetheless, winemakers don't measure sugar directly; instead, they look at its density levels. The formula for figuring a wine's alcohol content is complicated, but once winemakers identify what the grapes’ sugar content is, they can easily find out what future alcohol levels will be. Then it depends only on the varieties known “ideal” alcohol level and the winemaker’s preferences.

Whereas the pH of the grape juice is easier to verify, there is a device which does this readying in most winery labs. The usual values lie between 3 - 3,8, as within this range the chance of bacteria developing is near 0. The desired acidity levels is subject to personal taste, but the general guidelines are that values of 6 - 8 g/l for a Red and 7 -9 g/l for a White or Rosé are preferred by most consumers.

Subjective Analysis

Regardless of the technical data that winemakers find, the concrete facts about a grape’s maturity aren’t the singular determinant. A winemaker's skills and experience are put to the test when it comes down to a subjective analysis of the grapes, which means, sensorial experience must take the wheel.

During this subjective analysis visual, taste, aromatic, and haptic senses are brought into play, which complement the technical analysis in the laboratory. The combination of both will help to define the “ideal” date, which is indeed not only the combination of sugar, acid and pH but also the maximisation of phenolic compounds. One year a varietal’s optimum might be perfect with an alcohol content of 12%, another year we might need to target 13% in order to develop its typical varietal character.

The journey that leads to a divine destination

The art and skill that go hand-in-hand while crafting the most exquisite wines are factors only those in the vineyards can fully understand. As a wine’s composition is truly determined by the grape alone. The precise moment when the most crucial elements are in perfect balance to make a rich, soft, and rounded flavour is the moment grapes reach their peak. Contrary to popular belief, delicious wine is made not in a winery; but the vineyards themselves.

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Quinta Dos Vales, which has been named in the last 11 years both in regional and national competitions 8 times as “Best Wine of the Algarve”, currently has 180.000m2 of vineyard plantation, where grape varieties unique to Portugal, such as Touriga Nacional, flourish alongside international varieties. 16 small vineyards within this plantation are dedicated in the moment to The Winemaker Experience. This portion of land is long term rented by private winemakers from all over the world, and Quinta dos Vales plans to devote more plantations to The Winemaker Experience every year.

If you want to learn more about this subject, please consider joining as a private winemaker in The Winemaker Experience

Contact: Karl Heinz Stock


Organization: Quinta dos Vales – Agricultura e Turismo, Lda.Address: Sítio dos Vales, Caixa Postal 112, 8400-031 Estômbar, Lagoa (Algarve), Portugal