I am planning to brew 3 batches of Imperial Stout at the same time with the same recipe.
The difference is that I will age two batches with different oak cubes (one will be soaked in bourbon, one will be plain oak) and one will be left as it is. I want to compare 3 batches at the end. Anyway...
How many oz of cubes (assuming they are 1/2") should I use for a 5 gallon batch? How long should I keep them in the carboy, so I won't over-oak the stout (I heard that it might be an issue)?
Thanks.
Bear in mind this is for oak cubes, but I've heard a good starting point is between one to two ounces for at least two to three weeks. The lower the amount, the less oak flavor you'll get in a longer amount of time. The more oak you add, the more oak flavor you'll get in a less amount of time. Cubes have more surface area (therefor less contact with the beer and less/slower extraction) than chips, but less than spires or barrels, so your mileage may vary depending on what you read or hear from people. Also understand that people's responses to this will vary depending on how much oak they personally like, which may not match what you like.
With that said, your best bet is to start probably at 1-1.5 oz, let it sit for two weeks, draw a sample, and see if it is to your liking. If not, let it sit longer (or even add more oak). Don't be surprised if it takes in the upwards of months to get the flavor you're looking for, as the oak flavor will change over time. Be careful to not add too much oak, as it may impart undesirable intensity. Luckily if you do happen to over-oak your beer, it sounds like you'll have an oak-less batch that you can blend back in to the oaked batch(es) to help subdue the error.
The only way is to plan on tasting the beer regularly as the oaking occurs. For me it would be a matter of free time on my hands. If you think you can get in there and taste it every couple days using more oak would make things go faster. If you want to taste it once a week then less oak.
In general I agree <2 oz of oak is a good place to start for 5 gallons.
Keep in mind to that you get different flavors from the oak depending on how long it sits. Initially the flavor is predominantly woody raw oak stuff. But with more time the wood starts to yield more of the wood sugars and vanilla like cmpds. So its really hard to gauge that part of the process.
