Oak fermenting can have a variety of affect on wine, but in a good way. White wines fermented in oak include a pale color with an extra silky texture. White wines fermented in steel and then matured in oak will have a darker coloring. As far as flavoring of white wines that have been exposed to oak, you can expect notes of caramel, cream, smoke, spice and vanilla. Phenols within the wood interact with the wine, resulting in the vanilla type flavors. As far as red wines go, the degree of toast on the barrel will bring out varying degrees of mocha and toffee notes in the wine. There will also be a subtle vanilla and spice to the wine.

As for the barrel types, obviously oak is a common wood used to make the barrels. Other wood types that have been used include chestnut, pine, redwood and acacia. However, oak proves to be the best choice of wood because of its compatibility with wine; chestnut needs to be coated with paraffin to prevent excess wine loss through evaporation and redwood is too rigid to bend into smaller barrel shapes. Acacia brings out a yellow tint to the wine. It’s generally your best bet to stick to an oak barrel, it has proven historically to give off the best flavoring for wine, and stores the wine wonderfully.

Hope all this helps you out!