The Wine Wizard replies: In the home winemaking world there is quite a bit of debate on how to treat corks before they’re fed into the hand corker and forced down the neck of a bottle. What’s interesting is that, in the commercial wine world, there is no debate because no one boils, soaks or gets their corks wet in any way before feeding them through the corkers on commercial bottling machines.
Natural corks today have a coating that’s comprised of a mixture of silicone and paraffin wax. This coating helps protect the cork somewhat but most importantly, the paraffin provides the corks with a little tackiness (meaning stickiness, not the fake pink-flamingo kind) so that the cork doesn’t slip down into the neck of the bottle when it’s forced in by the corking machine.
I think the whole boiling and soaking thing is a holdover from the old days of winemaking. Back then corks were not very pliant and had to be softened by heat. In addition, water acted as a lubricant to help the corks get into the bottle. Also, corks were not very clean to begin with. So boiling was an attempt at sanitation. Though, technically, corks are never sterile, you can now buy nice, soft, clean corks in vacuum-packed bags from many sources. These newer corks are a breeze to use if you have a good hand-corker.
The results of your soaking routine are interesting. If you’re boiling your corks, you’re melting off the silicone and paraffin coating. You will therefore have a greater chance of corks not staying put once in the bottle (pushing out or sinking into the neck). This could possibly lead to more oxygen and microbes getting into your wine, a scary proposition.
Soaking for four to five hours in water similarly seems scary to me. At least while water is boiling, the water itself won’t get contaminated by any ambient bacteria or molds that might be floating around in the room or indigenous to the corks themselves. Soaking in plain water — not doctored up by anti-microbial potassium metabisulfite — for that long is just like asking the little buggies to come on in and go for a swim, not only in your soaking water but also your finished wine. I would try to bottle your wines without exposing your corks to water in the first place. If you find you need to soften them, or to use a little water for lubrication, make a strong (60 ppm free) sulfite solution and soak them for 15–20 minutes.