Can you make hard cider by pouring some yeast into a jug of store-bought cider and jamming a brewing airlock into the cap? IDK, let's find out!
Twelve hours after pitching the yeast, the cider has started to foam. I also poured some out, as several people pointed out I’ll need some headspace to prevent overflow.

OK, so two months later I bottled my cider in swing-top bottles, bottle-aged it for another couple of weeks, and I just had my first glass.

It’s…meh. There is nothing about it that is actively bad, but it's definitely not *good*.

Here's the challenge with homemade cider: it can either be sweet or carbonated, but not (easily) both. And this is *neither*, which is not a great combination.

When cider is done fermenting, the yeast has turned the sugars into alcohol. So it's no longer sweet. Also, the yeast has died off (because it ran out of sugar to eat or the alcohol got so high that the yeast can't live), so there are no longer any bubbles.

You can correct that by adding sugar just before you bottle it, if you kill off the yeast, which makes it sweet but not carbonated. Or you can add a bit of sugar before bottling, which will make it carbonated but not sweet.

I added a carefully measured bit of sugar to every bottle before bottling (too much and the bottle will explode), which somehow resulted in the cider being neither sweet nor carbonated. The bottle I opened was much improved through the addition of simple syrup, although of course it wasn't sparkling.

I've added a simple syrup to the other five bottles, and I hope to drink them at the perfect point when they're carbonated but still have sweetness.

IDK how much alcohol these have (I don't have a way to test), but the swimminess in my head tells me it's more than zero. I'll keep tweaking the remaining five ciders. I hope to learn enough to make cider from scratch next fall.

Backsweetening my cider did nothing to make it fizzy, so I added a pinch more yeast (which fizzed instantly) and waited a few days. I killed off the yeast with campden tablets, and just had some with lunch.

It’s pretty good! A little sweet, fizzy, entirely legit. I’ll enjoy drinking the rest, now that I’ve fixed them. And it all started by adding some yeast to a store-bought jug of cider.

@waldoj very cool. I still have some I need to bottle downstairs …