WINETECH Technical Yearbook 2020

mm inside staves. This is the temperature required to kill Brettanomyces. The treatment of barrels with hot water of at least 85°C for 20 minutes eliminates viable acetic acid bacteria if the temperature of the water is at least 60°C at the end of the treatment. This led to the development of a protocol for the sanitation of Brettanomy- ces- contaminated barrels by the Australian Wine Research Institute (AWRI). According to this protocol, Brettanomyces- contami- nated barrels can be sanitised to a depth of 5-9 mm in barrel staves by a water treat- ment of 30 minutes at 70°C or 20 minutes at 80°. These temperatures can be reached by filling barrels with water at 70°C and further heating it by using a spray nozzle of a hot water pressure pump. The decrease in temperature of the hot water is limited and water can be used four times before further

heating is required. The hot water can dam- age the stator of pumps and it must be con- sidered to siphon the water between barrels. Although the shaving and retoasting of barrels were considered a possibility in the past, it is not efficient to remove all viable Brettanomyces cells, which penetrate deeper into the wood. This treatment, as well as the treatment with dry ice, also require the removal of the barrel heads, which is a more elaborate process than the hot water treatment. High-pressure ultrasound treatment of barrels filled with hot water is also efficient for the Brettanomyces treatment of barrels, but special equipment is required to apply it. After barrels are treated, the success thereof must however be monitored. It can be done by filling the barrel with 4 L sterile water

the lifespan of barrels can be shortened. Sodium carbonate, potassium carbonate and peroxicarbonate solutions can leach the oak flavours. Due to the potential formation of chlorophenols and chloro- anisoles, chlorine solutions can also not be used. Although chitosan (a polysaccharide) is used by some winemakers to decrease the Brettanomyces population in wines, no information regarding its use for the sanitation of barrels is available. Steam can kill yeast up to a depth of 2 mm in cleaned barrel staves. Neither high-pressure warm water, steam, ozone, dissolved sulphur dioxide or sulphur dioxide gas can however deactivate yeast at a depth of 8 mm in barrel staves. Recent research has indicated that steam must be applied for at least 10 minutes to reach temperatures above 57.5°C at a depth of 8

or wine, without a preservative and leaving it for 24 hours after rolling the barrel. The liquid can be sampled and analysed for viable micro-organisms (Cowey, 2019). REFERENCES Anonymous, 2019. Brett on the rise again? Australian and New Zealand Grapegrower and Winemaker , October 2019: 50. Cowey, Geoff, 2019. What does the latest research say about barrel sanitation against Brett? Australian and New Zealand Grapegrower and Winemaker , October 2019: 76-77. helpdesk@awri.co.au.

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