After 48 hours, you can check for these three things just to make sure it’s working:
1. Take the airlock off and check for any new smells. Does it smell like things are happening? It should smell differently than your juice did at the beginning — often a bit yeasty or acidic.
It might not smell great just yet. Don't worry, any weird smells are just byproducts of fermentation — they'll go away in the next steps!
2. Shine your phone flashlight in your container, give it a swirl, and look inside. Are there any small carbonation bubbles moving around inside? That means that your yeast is producing carbon dioxide and alcohol, which means it's working.
3. Look at the bottom of your container. A layer of sediment should start appearing at the bottom - that means the yeast are reproducing, multiplying, and dropping to the bottom of your container!
If you're not seeing any of these things, your yeast may not be energized enough to do their job. If that's the case, you're going to want to briefly warm up your fermentation environment to re-energize your yeast and get them going!