Well, for a maiden seltzer voyage, I am not unhappy with the results. I started this batch on Sunday and after pitching the Lutra Kveik I didn't take great care to keep the ferment room within its ideal range of 80-95 degrees. I did turn on a space heater for the carboy for a few days, but it never hit 80 in that room. So here we are on Saturday, six days later, and I am damn near 100 percent attenuation. Gravity was reading 1.010 yesterday, it's halved the remainder today down to 1.005, so I think quite capable of doing the full attenuation job if I was willing to give it another day or so. I'm pulling the plug now so I can bring it to a party, um, tomorrow.
The mango puree with Everclear did strange things. The morning after I added the Everclear to the puree, I had mango cheese. It was like the mess just coagulated (looks like there is some evidence to suggest that mango, or its seed and peel, anyway, could serve as a natural coagulant . . . no, I didn't blend up the seed and peel with the flesh, though). Henceforth, if I wanted to come up with some sort of natural mango extract, I think I would definitely go with chunks, even if they were small chunks. Because of this reaction, I couldn't just strain the puree; it's like a fruit curd. It wasn't even like curds and whey in draining cheese; there was nothing to drain off. So I just racked the seltzer onto the mango curd, which was soft enough that it kind of broke up on contact and I'm letting it sit over night, then straining it off for party time tomorrow.
Even though it sounds like oxidation isn't as much of an issue with seltzers, I wouldn't treat it this carelessly if I didn't think most of it was going to get drunk tomorrow and that this was just a good learning experience. I definitely hear the folks advocating for just mixing vodka and not messing with fermentation at all. Perhaps it is the way to go if you're more focused on where you're going, not the journey, and looking for a higher quality overall end product. But I've gotta say, even if you didn't add any flavoring at all to the seltzer, I actually like the flavor the Lutra imparted on its own. It's very pleasant in an almost indistinct tropical way. Glad to know about Amoretto purees for the future. I'll report back again if we all think my finished seltzer is just godawful or anything, but dipping a spoon into non-mango puree territory after mixing in, the mango flavor is definitely already there and quite pleasant. It's mild, but seems appropriate for a seltzer.
Glad to hear the tip about the lime juice to brighten things up, and will probably try adding puree midway through fermentation if I do this again, as suggested. For this batch, we're just going to carb with a Soda Stream since it's so late, but there is a lot of natural carbonation staying incorporated in the seltzer from fermentation. I just had cheesecloth over the carboy opening, so it's really surprising that so much was preserved.