Raisins. Has anyone brewed with them?

[Know]

I covered 10oz Sunmaid Raisins with boiling water, puréed, and dumped into my oatmeal stout.

Secondary fermentation started back up within minutes. 4 days later I took a gravity reading and the sample was tart. The tartness masked nearly all other flavors. The beer is still very young so not mch flavor has developed, but damn does that prominent tartness have me concerned.

Anyone has experience with this?Should I rack off the raisins ASAP? Will this flavor recede? What kind of success have people had using raisins?

 

[secondbase]

I've only used raisins in a dark sour. I pan fried them with a little bit of framboise, pureed and dumped them into secondary to rack the beer on top. Grapes are highly acidic and tannic, so I knew they would play well with the character of the beer I was making. I'm not sure the acidity will decrease with time, but the tannins will mellow a bit.