"Matt A" wrote:

I found the following information:

" ... don't go out and buy commercial wine to top up your carboy (it will
probably contaminate it anyway) ... "

Is this true, will commercial wine contaminate ?????

It depends on your definition of contaminate. Commercial wine has probably
been sterile filtered, and pasteurized or sulfited, thus the chances of
microbial contamination are small. If you added a heavily-sulfited wine to a
fermenting wine, it could cause problems, but I wouldn't describe them as
contamination. But if you try to add Ripple to your Chardonnay or Cabernet,
that would certainly be contamination in my book.

An English tourist entered a small tienda in Catalonia, where he purchased a
bota (a small leather wine flask made of goat skin). As he started to leave
the shop, he turned to the proprietor and queried, "It's ok to use water,
isn't it?" The proprietor's face turned ashen. "¡No, señor!", he exclaimed.
"Water will completely destroy the insides!" The customer rejoined, "Are you
quite certain? I don't see how water could hurt the flask." The proprietor's
face returned to its normal colour. "¡Ai! la bota. I thought that you
intended to drink it".