Would it be OK to break in a new wine barrel by barrel fermenting some apple
cider? I don't want to "taint" the barrel with apple character that might
pass on to subsequent wines.

For the purposes of making an initial foray into barrel use, I chickened out
somewhat and went with a small, inexpensive 30 liter barrel made from
Portuguese oak. I was going to go Hungarian until a friend found references
that suggest Hungarian oak is fine for chips, but that they are harvesting
the trees too young to produce quality barrel staves.

Brian