Solutions under scrutiny to remedy cracking

Expertise and Experience

Cracking

What can be done to fight against the risk of cracking that is always a possibility on barrels? The Boutes cooperage is giving the problem its full attention and a number of possible responses are being tested out in the workshop. Cracking is a well-known phenomenon in all companies working in cooperage. “Wood is a living material and can always hold some surprises. The term cracking refers to the micro-cracks that appear in the most curved part of the barrel, the bulge, where the wood is under the greatest strain, especially around the bung-hole. They can appear visibly during production of the barrel or may be impossible to detect. It sometimes happens that cracking only occurs after one or two years,” explains Boutes Director Eric Besson. “The problem can even cause the stave to snap, although that is rather rare.” “Rather than having to deal with the problem once the barrel is on the client’s premises, we prefer to address it at its source.” Pre-toasting using an oak-wood brazier, over which the future barrel is placed, makes it possible to bend the staves. Cracking can affect all barrels, especially those with lighter toasting to allow the terroir and fruit to express themselves to the full in the wine aged in them. “This milder toast tends to leave the wood under greater tension and stress. Putting in the wine can then create further strain and a risk of cracking,” notes Philippe Trouvé, Quality, Safety and Environment Manager at Boutes. “We are working on this problem to eliminate the risk, while keeping our toasting profiles and the typical character of our barrels, like the Grande Réserve.” The cooperage has already taken measures in recent years to combat cracking. In terms of hygrometry, the staves of the barrel must not exceed a rate of 16%. “We also make sure that we do not exceed a width of 10.5cm for the stave with the bung-hole in it. The wider the stave, the higher the risk of micro-cracks, because the strain on the stave is all the greater,” points out Eric Besson. “To drill the bung-hole, we use a tool that goes more gently on the wood fibres, and to ‘cauterise’ the rim of the hole, we have had a machine specially made, that burns and evens out the area all at the same time, applying a backwards and forwards movement.”

Use of Lids

Cracking on the bung-hole

Another technique is also being tested at the cooperage: placing lids on the barrels. “After toasting, the barrel is left to stand. Its internal temperature remains high, so the heat passes through the wood and is also released via the open top, the ‘head’ of the barrel,” explains Philippe Trouvé. “By placing a wooden lid over the ‘head’ of the barrel, we force the heat to remain concentrated inside the barrel and escape slowly through the staves. The shaping of the barrel under the effect of the heat can thus be extended, thereby reducing the strain on the wood.” “The idea is to make the barrels more supple before they are trimmed by machine,” adds Eric Besson. Test protocols have been devised, with the barrels being placed under lids for various periods of time. Measurements are then taken to assess the risk of cracking. “We have created instruction sheets for these manufacturing inspection procedures,” explains Delphine Hubert. “Several hours after toasting, once the barrels are cold and arrive at the workstation where the ends are fitted, their head perimeters are measured. Each model of barrel has its perimeter. The measurements are taken on the ‘closed’ barrels, with their four working hoops,and then the same measurements are repeated with the barrels ‘open,’ meaning without the upper hoops.” "Once the hoops have been removed from the upper part, the barrel opens out slightly, as the wood tends to straighten out and return to its initial shape,” explains Philippe Trouvé. “The difference between the perimeter of the ‘closed barrel’ and that of the ‘open barrel’ must not exceed 8 centimetres. “Above this threshold, we consider that there is a risk of cracking,” says the Quality Manager. Series of tests will be conducted on the whole range of Boutes barrels. Their results will then be analysed to determine the right balance between the open and closed barrel perimeters, and the duration and characteristics of the toasting.