A recent trend for microbreweries and home brewers is to impart oak flavor upon their beer. Imbuing a beer with an oak flavor can be a good way of adding complexity or mellowing out other strong flavors in a beer.
Beer styles that typically benefit most from oak flavors are higher gravity stouts, porters, sours, traditional English Ales, and some Belgian ales. It is always important to use caution when adding oak to your beer because it is easy to overdo it and end up with a beer that tastes like a desk. Factors that impact the degree of oak flavor are the ABV of the beer, age of the oak, ratio of oak to beer, type of oak, toast of the oak, previous use of the oak, surface area, aging temperature, and aging time.
There are a lot of available options when it comes to imparting oak flavor on your beer. You can age the beer in an oak barrel, or you can add pieces of oak to your fermenter and age your beer with that oak. If you choose the latter option, you will need to decide if you want to use oak cubes, oak chips, previously used oak barrel pieces, an oak infusion spiral, or just chunks of oak. Each option has different potentials for flavor, so make sure that you choose the one that is right for you.
Oak cubes tend to be the most popular with home brewers. For most styles, you will want to add about 2 oz of medium toast new oak cubes per 5 gallons of beer, and allow it to age with the beer for 2 weeks to about a month. I would recommend sampling the beer each week to see if it has acquired the right amount of oak flavor, if it needs to be aged longer, or if it needs to have additional oak added.
A wide selection of oak additives for home brewing can be found here:
Here is a photo of the oak cubes that I added to my Russian River Consecration Clone. They were actual chunks of previously used Russian River Consecration barrels. I allowed the beer to age with them for about a month.
In regards to my Russian River Consecration clone, I first soaked the oak cubes in a Cabernet Sauvignon. Vinnie from Russian River recommends using a bottle of Kenwood if you will be soaking your cubes first.
If you are interested in purchasing a Russian River Consecration clone kit, they can be found here and sometimes have the oak included in the kit. Consecration Kit
I highly recommend the kit, but make sure you have at least 6 months available for the beer to finish up. Just let me know if you have any questions.