I don't re-use my oak chips. I don't think that it would be wise to do so. Spirals maybe but only if I am doing the exact same batch. The thing to remember is that wood is porous, as you extract you do infuse a little. There is a little back and forth. That's actually the point of it. To essentially flush out the good oils and have the oak ablsorb some of the undesireable flavors. Just a little. So rather than contaminate other batches with extra flavors and possibly yeasts or what not, I just use new. Also, I never sainitize the oak. Boiling the oak or other methods would also ruin what you are wanting from the oak.
Now some people like to soak the cubes/chips in burbon or other substances to subtly flavor (or in some cases not so subtle) their batch. That's great too. This is also why some people use burbon barrel cubes, to get that little extra flavor and trust me, it's there. Personally, I don't have access to this and don't care for burbon flavoring.
As for what to do with the oak when done? Makes great smoking oak for bbqing. Some of the mead flavors get into the meat, or if you are smoking fish, that's even better, more flavors get imparted at the slower smoking.
Also, If your oak chips look like sawdust then don't use it. Sift out the dust and toss that crap. That's not good for the mead. I had some hungarian oak that looked like sawdust, It made an bad after taste that I couldn't nail down until I did 3 batches with them. Tossed that oak. I am hoping that the bad after taste will age out.
Matrix
Actually, the infusion of past batches can be desirable.
Look at "Madame Rosemerta's Oak Matured Mead". It possesses remarkably subtle hints of liquorice and cherry... when not polluted by poison.
Ok, kupie doll to anyone who gets the reference.
But think about it. They do it with whiskies, they do it with scotch, they do it with many different types of wines and spirits. I think what's called for is a nose for it and experience, experience, experience.
That having been said, I would tend to worry about infections of one sort or another....
Brace yourselves, I just had a thought... I remember reading years ago that they had tested the 'cleanliness' of plastic kitchen cutting boards as opposed to traditional wooden cutting boards. Believe it or not, the wood was much more hygienic than non-porous plastic. It seems that the wood itself helps kill the little beasties.
Going to have to test this out some day.
Just some random thoughts,
Joe