Scraping the barrel for recycling
Wooden barrels are difficult to sterilize, but they are too expensive to use just once and then throw away.
Sophie Lecomte of Thales SA of France told the 2001 World Congress of the OIV (Office International de la Vigne et du Vin) at Adelaide that using second-hand barrels saves money but runs a risk of introducing off-flavors.
“It is an expensive process to control contaminants,” she said.
She said second-hand barrels are excellent value but bad maintenance can be the cause of the origin of phenolic characters in the wine and be the carrier of contamination.
“Chose only clean barrels for purchase,” she advised.
“Up to five liters of wine can be trapped in the wood of an empty barrel, in the tartrate layer or in blisters,” Lecomte said. “Wood is microporous. Bacteria can hide deep in the wood and are protected from sterilizing agents.
“Another problems is the stave joints and the fact that wood insulates bacteria from heat. It is a poor heat conductor,” she said. Microorganisms such as Brettanomyces can lead to ethylphenols or phenolic characters in the wine.
“Old barrels can contain up to 450[micro]g of ethyl phenols per liter,” she says.
Contaminating material is found on doors, taps, links, pumps and pipelines. Gutters and sewers are also often forgotten. These must be carefully cleaned and disinfected, she said.
Reconditioning Second-Hand Barrels
Traditional treatment consists of physically scraping the inside of the barrel and retoasting, but Lecomte says this risks tar or a burnt odor getting into the wine. Other options include steam and hot water, microwaves, ozone and chemical disinfecting.
Lecomte says treatment with hot pressurized water (90[degrees]C 130 bars) eliminates tartar and lees, but bacteria hidden deep in the wood can only be killed by very long treatment.
Heat treatment by steam and hot water removes aromas and residual tannins, but phenols survive several minutes treatment. On the other hand, a higher temperature can cause the bad tastes by action on molecules of wine remaining in the wood.
“Thermal treatment with hot water and steam is effective and will remove the tartrate, but it takes a long time,” she said.
Another cleaning system is to treat the barrel with microwaves after cleaning. Microwaves raise the temperature of the mass of wood uniformly without damaging the outer layers. This dry disinfestation can be carried out without washing away tannins and desirable residual aromas.
Lecomte says disinfestation using ozone is also becoming widespread, and ozone is limited to disinfecting. It is no substitute for thorough cleaning beforehand.
“Ozone is good for removing odors,” she said. “But this may give the operator the impression that disinfecting has been carried out when it hasn’t.”
Ozone gas destroys germs on inert substrates efficiently, but it may not be so effective on microporous material, such as wood. “Ozone is only at the empirical stage at present,” she said. “There are also possible health problems.”
Gaseous ozone can be hazardous to the operators. Under European regulations they should not be exposed to more than 0.2ppm gas. Moreover, traces of ozone can modify wine color, thus limiting its application.
“It is important to make the right choice of chemicals,” she said. A bad choice of chemical products can lead to loss of efficiency in the cleanliness plan. All disinfectants do not have a great spectrum of activity, and some can be totally inefficient against certain yeast contaminants.
If the cleanliness/disinfestation operation is carried out in a single stage, the chemical products used must include cleaning agents to eliminate dirt as well as disinfectant agents to destroy microbial flora.
“It is always better to operate in two steps,” she says.
Lecomte said wineries need to monitor their product flow and keep a watch out for cross contamination. Material such as polystyrene make good markers because of their strong affinity with this type of contaminant. Alternatively, contaminants may be absorbed on bentonite for analysis. However, this method is not sensitive enough to detect all contaminants.
“Adopt a product control plan which takes into account the different risk with each type of wine.
“Also, develop a cleansing plan, train staff to maintain cleanliness and audit operators’ performance,” she said.
(Frank Smith lives in Perth, Western Australia. He specializes in corporate and science writing.)
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