For beer aged either in oak barrels or on oak chips/cubes, does the contact with the oak noticeably affect final gravity, and if so, what is the direct cause?
Not really. In a discussion of the subject on the AHA forum recently, it was brought up that using barrels will increase the "angel's share"...the beer that evaporates. But it's such a small amount that it's negligible in terms of increasing the alcohol. Using chips or cubes should have no effect whatsoever.
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+1. Alcohol evaporates more quickly than water. Water won't evaporate through the barrel and leave a higher abv beer behind. – JackSmith Mar 4 '11 at 20:42
Not as long as the wood isn't infested with Brettanomyces, anyway.
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Even if it was that would be the brett not the wood causing a change in gravity. – brewchez Mar 5 '11 at 15:27
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1True, but if you saw a significant change in gravity after racking to a barrel, that would be an indication that you have something in the barrel that will eat "unfermentable" sugars. It addresses the "direct cause" portion of his question. – baka Mar 5 '11 at 15:56
