Lucky surprise for you! I greatly prefer my ciders to have a decent amount of sparkle. I'm still relatively new to cidermaking, but I like to run my primary fermentation down to SG 1.000 (or even less) but that obviously leaves a really dry cider. I back sweeten with a nonfermentable sweetener (I like splenda best) and then add a bit of tannin and also a nice high-quality dark maple syrup as a primer. I've used honey as well, but prefer the maple as it gives a bit more body. I then bottle it and allow it to use the primer to naturally carbonate in the bottle. I obviously don't use any sorbate or K-meta as that would prevent the natural carbo. Using about 500gm of maple syrup per 5 gallons yields a carbonation level of about 3 volumes which is moderately fizzy if all goes well and the bottles don't leak. When bottling, I fill one plastic bottle like a 16oz soda bottle or a 1/2 gal plastic cider bottle (both sanitized) and then use glass flip top bottles for the rest of the cider. I let all of the bottles sit out at room temp for several days while priming. When the plastic bottle is VERY firm, I put them all in the fridge to markedly slow the fermentation, and then *fingers-crossed* most of the primer should be gone by then too. I use flip top bottles of decent strength and so far (knock on wood) haven't had any fridge grenades.
Exciting that you seem to have gotten a natural carbo without even really trying...now good luck trying to replicate it!
Cheers, Stretch
