Any know how to go about doing the Cluster 16+ that the Bent Spoke in Canberra brew?
All quad IPA recipes I've found come in at no more than 10% ABV but they get 16%+ whilst still being a beer, not a barley wine. The balance of malt, hops etc is perfect.
Any thoughts?
Are you interested in Cluster 16, which is more of a Belgian Quad with some vague leanings towards being an IPA (16% and only 52 IBU), or Cluster 18, which is a frankly insane sextuple IPA at 18% and 160-odd IBU? You said 16, but you should know that it's really not a Quad IPA at all.
At 16% Cluster 16 is on the high side for a quad, but only a little outside the usual ABV range for Abbey/Trappist yeasts (Wyeast 1214, WLP500, WLP530 etc). Those should make it to 12-14% with no real difficulty. Getting it up to 16% can probably done with oxygen and a really big pitch - a massive starter, or the yeast cake of a lighter beer.
I'd probably go the second route if I wanted to try this - brew up a normalish Tripel (maybe, I dunno, 8%) and then rack your crazy-high gravity Quad wort onto that yeast cake.
The recipe itself would be dead simple - a lot of pilsner malt, a little less pale malt, belgian candi syrup, maybe a touch of cara-pils or carahell. There's lots of quad recipes out there - this one is much too small but very well regarded, so you might try scaling from here:
https://www.homebrewtalk.com/forum/threads/westvleteren-12-clone-multiple-award-winner.500037/
I haven't tried Cluster 16 so I have no idea how it's hopped. I think it's a reasonably traditional trappist quad, though, so I'd just pick a recipe and roll with it.