Now for the opinions and comments...
Current lineup of the covenant's magi: 3 Bonisagi, 1 Criamon, 1 Jerbiton
Note that we also have one dedicated brewer for the covenant (covenfolk), one grog who has brewing as a hobby, and the Jerbiton magus came with another covenfolk who is a high-quality low-quantity vintner. And there is a companion who is a magical cooper. So if all of these are fully exploited, you may find the niche crowded.
I would have a tendency to rule out another Bonisagus, particularly if he comes from Egypt. Ex Misc is always a possibility, though that means creating a lineage. I'm not personally fond of Merinita, but if it floats your boat I'd be fine with it. Verditius definitively has potential. Verditius certainly, for the alchimical side and all the apparatus for brewing. Have you thought about an unlikely Flambeau magus? He might be more into the distillation than straight brewing, although temperature control would certainly fit nicely into his magical capabilities.