How the Summer Shapes our Wines

Rathfinny Wine Estate produces vintage Sussex Sparkling on a single-site Estate in the South Downs. The elements that contribute to making our wines different, year to year, are varied and – to be honest – quite technical. We reached out to our Winemaker, Tony Milanowski, to shed some light on the topic.

By Tony Milanowski, Rathfinny Winemaker

It’s complicated. As a vintage wine producer, each year we bring the grapes in from the Vineyard to the Winery to make our wines. Each year, the fruit is slightly different.

Depending on the amount of sun, rain, wind and the temperature – along with a host of other factors – across the growing season, the grapes will take on special characteristics. As we do not blend between the years and make a mass-produced style of wine, each year we make English Sparkling wines that are, although delicious, all different.

For this blog, I took a look back at notes from my days lecturing at Plumpton College to answer some of the common questions on how different factors shape the final flavour of the wine, making each vintage unique and special.

WHAT GRAPE COMPOUNDS CREATE WINE FLAVOUR?

A grape berry holds the compounds which are the foundations of wine flavour: sugars (for alcohol and aroma release), organic acids (freshness, structure, longevity), phenolics (colour, texture, ageability), minerals/ions (salinity and tertiary aromas), plus aroma from the grape and the secondary aroma precursors that yeast reveals during fermentation.

These different compounds in the grapes evolve, increasing and decreasing as the fruit grows and ripens. How the grape develops depends on a multitude of external factors, meaning that a single vine can produce fruit with remarkably different characteristics from one year to the next.

HOW DOES SUNLIGHT AND TEMPERATURE CHANGE GRAPES AS THEY RIPEN?

Unripe grapes start out with a fixed amount of malic and tartaric acid. As the berries swell and take up sugar from photosynthesis, the acidity becomes diluted. At the same time, the grapes are respiring, which slowly removes some of the malic acid. This is where temperature plays a big role: in warm weather, respiration speeds up and more acidity is lost; in cooler weather, the fruit holds onto its natural bite. In England’s cooler climate, it is no surprise then that the final fruit has great freshness and longevity – perfect for making wines that can spend time in the cellar and still be deliciously refreshing and crisp.

Sunlight also leaves its mark by shaping the grape’s phenolics, the natural compounds that influence colour, taste and mouthfeel. Exposure to UV light stimulates flavonols (the grape’s own sunscreen) and supports development of darker colour pigments known as anthocyanins, the pigments that give red grapes their vivid hues. The sweet spot for these red-skin pigments comes with cool nights around 15 °C and mild days near 25 °C. Too much heat, especially in the 30–35 °C range, can cause pigment loss which is why growers carefully manage the vine’s canopy to juggle exposure and shade.

Even in delicate sparkling wine bases, these shifts in acidity and phenolics subtly shape the wine’s hue, texture and longevity.

HOW DO ACIDS LIKE TARTARIC AND MALIC SHAPE FRESHNESS?

Two main acids shape a wine’s freshness. Malic acid naturally breaks down as grapes ripen, and this happens faster in warmer weather or as the berry’s cell walls become more permeable. As malic levels drop, the sharp, tangy edge in the fruit softens.

Tartaric acid is more stable and tends to dominate at typical wine pH. Around pH 3.4, tartaric acid can contribute about three times more acidity than malic. This balance between the two doesn’t just affect taste but also influences colour, stability and how well the wine resists spoilage.

HOW DO MINERALS AND PH AFFECT WINE BALANCE?

Of all the minerals in grapes, potassium (K⁺) plays one of the biggest roles. It moves easily through the vine, helping sap flow and moving from the leaves into the fruit to support ripening. If the vine’s photosynthesis is limited, say by heavy cloud cover, even more potassium shifts from the leaves into the grapes. This can raise the juice’s pH, softening its acidity.

In warmer seasons, the pH of the freshly crushed fruit often comes down to the balance between tartaric acid and potassium levels. The final pH balance of the wine which goes a long way to deciding how the wine feels on the palate, so if there is too much potassium and not enough tartaric in the final grape must, the wine can feel flabby and lacking in balance.

WHAT WINEMAKING CHOICES HELP CAPTURE A GROWING SEASON’S CHARACTER IN THE FINAL WINE?

Given Rathfinny has a single-site and only produces vintage wines, our aim is to reveal the character of the season in our English Sparkling wines through considered winemaking. It is about enhancing what we naturally have in the fruit to make terroir-driven Sussex Sparkling. Several choices help:

• Time of Harvest: Choosing when to pick is one of the most important decisions we make. Ripeness is key, and it varies not just between grape varieties and clones, but also across the Estate’s Vineyard. Even within a single site, subtle differences in wind, altitude and aspect create contrasts from one block to the other. By harvesting a block – or parcel of fruit – at the right moment and blending thoughtfully, we make wines to our full potential.
• Gentle pressing: extracts the purest juice while limiting bitter phenolics from skins and seeds. Pressure, time, temperature use influence flavour and texture. Some winemakers would also add enzymes at this stage to break down the grapes to support juice extraction. At Rathfinny, we choose a more low-intervention philosophy and do not use enzymes at this stage.
• Yeast selection: However, at Rathfinny we aim to make terroir-driven wines with the quality of our fruit shining through, so we use neutral yeasts that retain the character of the primary grape aroma. In contrast, there are specific yeasts that can help unlock delicate floral, citrus or stone fruit notes in fruits.
• Low-dosage approach: minimal sugar added at disgorgement keeps the fruit pure, highlighting the poise and sense of place unique to each vintage.