I've retired a few barrels this week and began considering their next phase of life. These are medium-toasted Am oak 53-gal barrels, for the interested. For the last 5 years they have been in continuous use aging various red wines and so are pretty much neutral oak now. One possible life for them would be to use them as fermenting barrel for a white, such as chardonnay or viognier. However, the natural question that arises is whether they can be sufficiently cleaned (without disassembling) to avoid a pink hue to the white wine. I've already rinsed them several times using a barrel spray ball, caustic wash (1% NaOH), and finally citric+sulfites. However, I'm not convinced that the rinsate is perfectly clear enough for me and that there are not hidden tartrates in the crevasses that are waiting to give a pink hue to a white wine. Thus the question: what steps, if possible, are suggested to satisfactorily condition a previously used red-wine barrel for use as a white wine fermentation barrel?