South Africa Wine Technical Yearbook 2025

faults (for example Brettanomyces ) not tested for on routine basis can be noticed in this way. The sensory development of wine in the barrels should also be monitored. • Detailed records of the barrel analyses, including sensory evaluations, should be kept. This allows winemakers to gain a better understanding of the wine’s development over time. Drawing wine samples The use of a curved stainless steel or glass wine thief is the most suitable method for drawing wine samples from a barrel. The opening on top of the wine thief is pressed shut while the wine thief is lowered into the wine in the barrel. By then lifting the finger from the opening, the wine will slowly fill the wine thief. As soon as it is full, take out the wine thief and carefully transfer the contents to the sample bottle. If a composite sample has to be assembled, the sample should be taken as reductively and carefully as possible to avoid excessive oxygen uptake, which can cause a false reading on the free sulphur analysis. Bungs A well-sealed barrel ensures that the wine is protected against oxidation and contamination. It is important to inspect the condition of bungs regularly. Over time, bungs can become worn, causing the fit to be too tight or loose, which can have negative effects on the wine. Bungs should be replaced as needed to maintain the integrity of the maturation process. Currently, there is a wide variety of bung closures available on the market. All of these come with their own set of advantages and disadvantages. There is even an electronic version (e-bung), which can send the temperature and volume of a barrel to a cellphone to warn if certain parameters are exceeded. Temperature, humidity and CO 2 Barrels must be spaced in such a way as to allow for good airflow around each barrel. This promotes the control of temperature, humidity and CO 2 levels around the barrel. The most acceptable barrel storage room temperatures for winemakers in South Africa are between 16 and 18°C. The temperature influences the maturation process of the wine, and temperatures lower than 16°C will result in slower development of the wine, whereas temperatures higher than 18°C will lead to higher losses and accelerated development. It is important to make sure that the temperature-control

system is functioning properly on a regular basis (at least every other day). Especially after power outages, these systems tend to not restart automatically and this can lead to a drastic increase in barrel storage room temperature. The ideal humidity in a barrel storage room is between 75 and 85%. Anything lower will result in greater wine losses over time, and anything higher can promote fungal growth. To maintain an appropriate humidity, wine cellars must be equipped with humidifiers or moisture-control systems. Keeping the doors of the barrel storage room shut as far as possible is very helpful in controlling the temperature and humidity effectively. If systems are not set up to regularly allow the inflow of fresh air from outside, it is a good practice to open the doors at least once per month for a while to allow entry of fresh air. VERY IMPORTANT If, however, there are barrels in the storage room undergoing alcoholic fermentation or even malolactic fermentation (MLF), the control of carbon dioxide (CO 2 ) is extremely important as high levels thereof can be life threatening. The barrel storage room, in this case, should have very good ventilation, and the CO 2 levels should be monitored with gas detectors. An alarm system should warn workers to leave the storage room immediately if CO 2 levels Hygiene is of utmost importance in the barrel storage room to prevent contamination by spoilage micro-organisms. Regular cleaning and sanitation of the storage room and barrels are essential. The whole storage room, including floors, walls and equipment, must be kept clean. One of the best solutions to keep unwanted micro organisms under control is to install a UV light behind the fans in the storage room. These lights can be connected to a time-controlled switch and, depending on the size of the storage room, can be switched on for a set period per day. There is also an option available of UV lights that produce ozone (O₃). The fact that the ozone gas can penetrate where the light is not necessarily able to makes this option very effective. This same type of light can also be used to sterilise barrels, providing a fantastic alternative to burning sulphur strips in barrels. When sulphur strips are, however, burned, take care to ensure that the room is well ventilated and that staff wear the required PPE (personal protective equipment). rise beyond a safe concentration. Barrel storage room hygiene

Conclusion Each storage room aspect, from barrel stacking to the precise control of temperature, humidity and hygiene, plays a key role in upholding the quality of a wine. Maintaining a constant barrel storage room environment will ensure that the wines reach their full potential in the maturation process and develop the characters desired by the winemakers. 

For more information, contact Pieter Badenhorst at pieterb@fortheloveofwine.co.za. Reference https://www.wineland.co.za/guidelines-for-the-management-of-barrel-storage-rooms/

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TECHNICAL YEARBOOK 2025