Begin by slicing the cabbage very thin with a sharp knife or mandolin, being extra careful if you're using the mandolin.
Grate half the apple leaving the remaining half. Finely chop the chilli and grate the ginger. Add these to the large bowl of sliced cabbage and mix thoroughly.
Sprinkle the salt all over the red cabbage mixture and stir so that it's fully incorporated then leave for 20 minutes. This gives the salt time to work on your ingredients and begin drawing out water from the vegetables which will start to soften.
Go back to your bowl and with clean hands start to work it all together. You need to grab handfuls and squeeze the red cabbage mix tightly over and over again until it becomes really wet and a big puddle of gorgeous pink liquid builds up at the bottom of the bowl. This mini work-out should take about 10 minutes.
You want it to produce so much water that, once it's packed into the jar, the cabbage is completely submerged. This is REALLY important because it will keep the sauerkraut fresh while it's in the anaerobic environment and prevent it from going mouldy.
Pack the mixture into your jar and press it down to get it all in.
Take the apple half and stuff it on top of the sauerkraut to make sure it’s completely covered in the liquid. There needs to be a gap between the completely submerged sauerkraut and the lid of 1-2 inches.
Put the jar of sauerkraut on a plate and burp it (open the lid and let the air out) every day to let the build up of gas out of the jar so it doesn’t explode! Allow your sauerkraut to ferment for a minimum of 3 days and up to 2 weeks before popping it in the fridge to hold the flavour where you like it.