Here are some comments and insights into this year's harvest in Elgin.
By Richard Kershaw MW
As the whirlwind of the 2024 grape harvest begins to dwindle, I've managed to carve out a moment to share insights into this year's harvest and address the key questions that have surfaced amid the vines.
As most of you know, I love delving into technical details (as below). Click on the word links for easier-to-understand translations and definitions added by Sarah.
The Growing Season
The 2024 growing season presented unique challenges, with record-breaking winter rainfall persisting into September, followed by notable heat spikes in January. Despite these conditions, our vineyards experienced relatively normal bud break and flowering timings. However, the grapes exhibited signs of dehydration due to the intense heat, prompting us to exercise patience and allow for sugar and acid stabilisation before harvest. We're currently in the late stages of the harvest, and while it's still premature to make definitive assessments, the vines have shown promising signs of resilience and quality so far.
Overcoming Challenges with Patience
One of the primary challenges this year stemmed from the erratic weather patterns, particularly the heat spikes, which led to higher fructose levels in the grapes (see below section) and the slight dehydration that the vines experienced during this short passage of time (see below). Additionally, diminished cloud cover increased our UV exposure, hastening ripening processes and necessitating meticulous vineyard management strategies.
Tackling the fructose issue first:
It is known that fructose increases with ripening, but a few other juice characteristics also change. Total acids tend to drop, with malic acid dropping faster than tartaric. The potassium content of the juice rises, which has implications for further acid dropout as it interacts with tartaric acid to form insoluble tartrates. Yeast available nitrogen (YAN) also falls with ripening. Looking at the GFR (glucose-fructose-ratio) in conjunction with these other parameters can give a winemaker an indication of how stressed the vines were before harvest and the potential for problems during fermentation. Looking at the juice before fermentation will provide winemakers with an indication of whether a natural fermentation would be feasible.
During fermentation, the membrane transport system tends to favour glucose over fructose. The concentration of fructose, vitamins, and nitrogen in the juice can influence this degree of preference. The rising alcohol concentration as the fermentation progresses also slows glucose uptake.
Getting such a wine going again often requires using a selected Fructophilic yeast and specialised nutrients.
Wines that finish fermenting but end up with more residual sugar in the form of fructose can have the following characteristics.
Wines with higher residual fructose can taste sweeter, even if the total amount of residual sugar is low. This is often the cause of undesirable sweetness in dry wines, as fructose tastes almost twice as sweet as glucose.
Elevated residual fructose levels correspond to reduced ethanol, yielding an altered mouthfeel.
Given the fundamental understanding of glucose and fructose’s role in fermentation, proficient winemakers are equipped with the necessary insight to avoid the dreaded ‘stuck fermentation’.
In a vintage with an undesirable GFR, winemakers can either manipulate it to their advantage or ensure that the yeast has enough nutrients (such as nitrogen) and optimal fermentation temperature to get it safely through the entire fermentation. While these methods can help prevent a stuck ferment, they are not foolproof. Winemaking is as much an art as a science; even the most experienced winemakers can encounter challenges. However, by understanding the role of glucose and fructose in fermentation, winemakers can make informed decisions and increase their chances of producing a successful batch of wine.
On the UV light, cloud cover and abscisic acid:
Abscisic acid (ABA) is a plant hormone that plays a crucial role in various physiological processes, including grape ripening. One of the critical functions of ABA is its role in promoting sugar accumulation in the berries by enhancing the translocation of sugars from the vine to the berries.
Its synthesis is in response to cues such as water stress, temperature fluctuations and light exposure.
Consequently, a reduction in cloud cover precipitates an augmentation of ultraviolet radiation, particularly UV-B, which catalyses the process of grape ripening through enhanced sugar accumulation. Concurrently, the development of the grapes’ flavour profile and phenolic maturation unfolds at variable rates of reaction kinetics, resulting in protracted periods of grape maturation on the vine, potentially yielding wines with elevated alcohol content due to prolonged exposure to the elements.
Inversion Layer:
A last challenge was that during early February, we experienced an inversion layer that formed over 3 days. Typically, according to the adiabatic lapse rate, the temperature decreases with an increase in elevation – usually around 0.7ºC for every 100 metres. This means Elgin, at 300-500 metres elevation, is commonly far cooler than Somerset West and, along with its proximity to the sea, is around 6-10ºC cooler than Stellenbosch.
However, on these three days, we had a high-pressure system and a very stable air mass that trapped cool air near the surface beneath a layer of warm air, thus inverting the temperatures. These warmer nights slightly dehydrated the berries and thus gave unusual sugar readings on the refractometer that often were higher than expected.
Once the inversion layer had been alleviated by cooler weather and, importantly, cooler nights, the berries rehydrated their shape, resulting in lower, more normal readings for that time of year.
All in all, the key was to navigate this challenge by closely monitoring phenolic ripeness alongside sugar ripeness, ensuring that our grapes reached optimal maturity before harvest – i.e. avoid panicking!
Optimism for Quality
As we progress through the harvest, we are optimistic about the quality of our Chardonnay and Pinot Noir grapes. Early indications suggest that despite the initial weather hurdles, our vines have adapted well, yielding fruit with a notably lower pH and excellent flavour potential; however, it is premature to project specific outcomes currently, and we haven’t finished picking Syrah yet.
Unique challenges have characterised the 2024 grape harvest season; diligent monitoring and management allowed for the navigation of these obstacles. Overall, this season underscores the necessity of adaptability and patience in the face of environmental variability, offering insights into the interplay between viticultural practices and grape quality outcomes.
Here are some definitions for the terminology that I used in this article:
Adiabatic lapse rate: The rate at which atmospheric temperature decreases with increasing altitude in conditions of thermal equilibrium.
Phenolic ripeness: Phenols, which comprise of tannins, among other compounds, are intricate molecules found in grape skins, seeds, and stems capable of imparting bitter tastes. As the grape matures, its phenolic profile transitions from harsh and green to pleasantly astringent, eventually culminating in a soft, ripe flavour.