Mother Nature has shown us very little mercy for the 2015/2016 growing season. We experienced some unseasonably warm temperatures in January which kept us on our toes in terms of how we manage our precious vineyards at De Toren. Not only have we had the heat to contend with but we are faced with looming water restrictions after a particularly dry winter in the Cape. Our water is sourced from the Theewaterskloof dam, which was only at 49.7% capacity at the time that this article was written. This is an alarming statistic considering that the last 20% of a dam’s capacity is comprised of sludge and cannot be utilised.
The team at De Toren has always married years of experience with specialised scientific techniques to read each of our blocks for signs of stress and make precision irrigation decisions. The ability to make precision irrigation decisions has been especially important this season in light of persistently warm conditions and looming water restrictions.
In 2006 we acquired a piece of machinery that will revolutionise our understanding of each of our different vineyard blocks and, importantly, how to manage their specific water stress levels when irrigating. This specialised machine is called a Pressure Chamber and we are still one of the lucky few farms in the area to have one.
This machine uses the pressure of inert gas to squeeze water that is present in the vine’s leaf, out through its leaf stem. The amount of pressure it takes to push this water out tells us the level of water tension in the leaf. This is an indication of the vine’s degree of difficulty in accessing water from the soil.
The readings are a particularly important indication of the vine’s stress level and the amount of accessible water present in the soil. This is crucial information that helps the team to track stress levels which may negatively impact the vine’s ability to ripen fruit. Using this information, and being cognisant of how the various grape varieties differ in the manner in which they handle stress, we can make an informed decision about the optimal timing and duration of irrigation for our individual blocks.
Managing water stress in our vineyards is a fine art. While vineyards are channeling their energy into vegetative growth and the cells are dividing to make glorious green canopies and what will become our precious bunches, the vine needs to be kept comfortable and happy. If a vine experiences excessive water stress during the vegetative growth cell division period, it can drastically reduce berry size and therefore our crop load. A reduction of 1mm in berry diameter can result in a 20% reduction in berry volume, which can have a detrimental impact on the harvest.
While you want to keep your vines free from stress whilst they are growing and developing our valuable bunches, when veraison (the French term for onset of ripening) has reached 100%, the vegetative growth should cease. Once vegetative growth has ceased, the vine can focus its resources into ripening its bunches. Research has shown that vines which experience moderate levels of water stress from this period, produce superior quality fruit. By ensuring that there is a moderate level of stress, the vine is not encouraged to push out any new growth in the roots or canopy, thereby pulling important resources away from bunch ripening as the vine supports new growth.
Veraison is an important phase in the vineyards when the berries are no longer increasing in size due to their cells dividing, but begin to ripen as the vine directs the sugars it produces, to the bunches. An important indicator that veraison has begun is a change in colour of the grapes which begin to soften as the green chlorophyll molecules are broken down and pigments called anthocyanins which – give the grapes and ultimately the wine its colour, are formed.
This colour change and the onset of ripening is catalysed and facilitated by enzymes in the berry. Most chemical reactions occurring in nature are catalysed by enzymes, such as the ones that help us digest our food so we can absorb the nutrients. Enzymes are proteins and they are influenced by the temperature of their direct environment. As I mentioned, we experienced some unseasonably high temperatures in the early part of this growing season, which had an effect on the veraison phase in our vineyards.
In very high heat, the berries heat up to a temperature which makes it too hard for the enzyme to work, so the enzymes responsible for these ripening processes are put on pause. Normally the colour change we can see at veraison takes about two days to change from green to black through a vineyard block. Because these enzymes were paused due to high day time temperatures, some blocks took more than two weeks to turn from green berries to black.
We apply a green harvest action to remove green bunches that are behind in their ripening process compared to the rest of the bunches around them. Firstly we remove any wholly green bunches when the block is showing 80% completion of veraison. Then we go into the block closer to 95% and remove any bunches that have not coloured sufficiently in comparison to their neighbours. Finally to maximise consistency in our bunches for harvest, we go through each row and remove individual berries that have not coloured in a final action. Green harvesting is one of the critical quality control parameters to ensure that our blocks are ripening homogenously. This is so that when we pick our fruit, we are not picking slightly under ripe, ripe and slightly over ripe fruit for that block. The green bunches and berries that are lagging behind with their veraison, will never really catch up in terms of ripeness and will dilute the quality of fruit we pick from the rest of the block.
Green harvesting may mean that we lose bunches but we will never compromise quality over quantity at De Toren as we strive for perfection in everything we do.
With harvest around the corner, we hope for moderate temperatures for the balance of the growing season, a fruitful yield and lots rain for our thirsty vines post-harvest. By then they can take a well-deserved break whilst the hard work for the cellar team begins.