Commonsense winemaking – Brief Article
Richard G. Peterson
Q: The previous winemaker always used a 1% citric acid soluto neutralize excess chlorine after sterilizing tanks and equipment. He swears by it but can’t tell me why it works or what concentration of citric acid is optimum. How do you recommend I do it?
Sounds like we’ve just put our finger on why you’re the new winemaker. Citric acid and chlorine reacting in dilute solution at ambient temperatures is not chemistry; it’s witchcraft. Citric acid solution doesn’t remove residual chlorine any faster than plain water does. I’m always amazed at how these old wives’ tales in chemistry get started and how rapidly each one spreads among winemakers. The beliefs often change for the worse after they’ve been around for a while.
I believe this is a confusion caused by the fact that citric acid was used for many years to neutralize excess soda ash after the soda ash was used to treat new American oak barrels before their first use. It removes soda ash very well, because soda ash is alkaline and everybody knows that acid kills alkali instantly. It removed soda ash so well that, maybe, citric acid in some circles became “the thing to use” for removing all chemicals (including chlorine) from barrels. Too bad it doesn’t work against chlorine: Damn textbook chemistry, it can ruin simple and easy cellar practices every time.
Well, you ask, if citric acid does not react with chlorine in dilute solution, what does? Sulfur dioxide does–and fast! One of the cardinal rules of chemistry is “never mix an oxidizing agent with a reducing agent.” To a winemaker, this means never store dry chlorine next to dry [SO.sub.2] in a winery. (Never allow dry, “swimming pool” chlorine powder to contact dry meta bisulfire powder.) If the two dry chemicals somehow get into contact and the mixture hasn’t exploded yet, well, it won’t be long! Flood the mix with cold water as soon as possible.
But in dilute solution, that’s a horse of a different color. After washing barrels, tanks, hoses or other equipment with chlorine and rinsing it off, there remains a significant residue of chlorine which would be damaging to the equipment if not removed promptly. Even stainless steel becomes pitted if allowed to stay in contact with chlorine repeatedly! Worse, any wine contacted by chlorine (even as little as a few ppm) would be ruined promptly, and irreversibly.
To remove this chlorine residue, simply mix up a dilute water solution of [SO.sub.2] and rinse away the chlorine with that. A barrel or wood tank which has been sterilized with chlorine solution should be rinsed with water, then filled with [SO.sub.2] solution, emptied, rinsed and presto, it’s ready for wine use. If it has to stand empty for a few weeks, then burn a partial sulfur wick in each barrel after the [SO.sub.2] rinse and before storing the empty barrel or tank. The chemistry is: [SO.sub.2], a reducing agent, reacts instantly with chlorine, an oxidizing agent of renown. In dilute solution, there’s no danger and they’ll neutralize and remove each other very quickly. Since [SO.sub.2] in ppm amounts doesn’t harm, but actually protects wine, always be sure you end up with excess [SO.sub.2] and never excess chlorine. If you do this, the concentration used is unimportant.
Can [SO.sub.2] be used to remove other oxidizing agents? Sure, same chemistry. Take ozone, for example. It’s a strong oxidizer like chlorine except that it can’t occur in a dry powder form, and the breakdown products of ozone are only water and oxygen. So it’s safer to use in many respects. But ozone, if added to wine in significant amounts, will certainly ruin the wine in the same way that chlorine will, by oxidation. Just be sure you have enough [SO.sub.2] in the wine to remove any excess ozone that might be there, and you’ve dodged a bullet.
But save your citric acid for acidifying. If anybody still uses soda ash to clean oak barrels, rinse with a little citric acid to remove residues of soda ash and re-acidify the wood surface. If the soda ash has been soaking in barrels for a day or two, traces of it will have penetrated into the porous wood. To get all this out, it’s a good idea to actually fill the rinsed barrel with citric acid solution, soak a while, then empty and rinse again with water, drain and use the barrel for wine (burn a quarter wick of sulfur in each barrel if it is to be stored longer than a day or two prior to refilling with wine.)
Of course, very few winemakers use soda ash any more for barrels. It hasn’t been necessary since barrel makers started using fire to bend hoops rather than following the old whiskey practice of using steam. More about that in a future article.
Group Arnault Forms Internet Investment Company
Group Arnault is the holding company that controls LVMH Moet Hennessy Louis Vuitton. The new company, Europe@web, will invest, via the Internet, in companies in Europe and the United States. Europe@web will create links with such European operations as Vivendi. Among LVMH’s holdings are Dom Perignon, Moet & Chandon, Hennessey and Mine cagnacs, Veuve Cliquot, Krug and Pommery champagnes and Chateau d’Yquem.
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