Place the shredded red cabbage, sliced onion and smashed garlic clove in a large jar.
Add the apple cider vinegar, water, cane sugar and sea salt to a small saucepan. Simmer over a medium heat until the sugar and salt have dissolved. Pour this brine mixture over the cabbage in the jar.
Cover with a lid and shake to completely submerge the cabbage in the brine. Uncover and leave to cool to room temperature. Cover and chill for at least 1 hour prior to using.