On your next brisket, try hickory, a low tannin wood. Oak has a higher concentration of tannin which might lead to bitterness. Regardless of what wood you are using, if the smoke is heavy and grey, it will be bitter. Here is good article, more information than actually needed but interesting none the less.
http://amazingribs.com/tips_and_technique/zen_of_wood.htmlThanks for sharing Dave. Interesting read. I thought I had thoroughly researched that topic but clearly there are numerous factors to consider. I found it interesting that a tree's locale and soil will affect the smoke even more than the type tree. Here in my home state of Texas, post oak is the favorite of some of the top pitmasters for it's alleged "milder smoke". But those articles neglected to mention tannin content. I'll be ordering some quality hickory and/or pecan to try next time!