Use of new oak barrels

[wondersofwine]

When a vintner says he uses 25% new oak (or 50% of whatever) does that mean that only 1/4 of the vats he produces are in new oak (how would you ever know which ones until you taste them?) or does it mean that the forming wine spends 25% of its time pre-bottling in new oak casks and then goes into old oak casks or stainless steel?