It is crucial to stick to the correct salt ratio and not just eyeball amounts to make sure you create the right environment for good bacteria to thrive and bad bacteria to stay out. Your salt to veggie ratio should be anywhere between 3-5%.
Oxygen exposure can lead to spoilage and mold growth, so make sure to fully submerge everything in brine.
The first few days will create lots of activity and potentially overflowing brine from the jar. Make sure to place a small plate underneath and 'burp' the jar if needed to release gasses.
Once you’re happy with the taste and fermentation time, move to the fridge to slow down fermentation. The sauerkraut will last up to 1 year in the fridge.