Loosely pack the sliced cabbage into the jars adding the caraway seeds and juniper berries throughout. Leave enough room at the top of the jar to allow enough liquid (the brine) to be added.
Pour the brine over the cabbage mixture and gently push down the cabbage to ensure that it is fully submerged under the brine and that any air bubbles have been released.
Cover each jar loosely with a lid. You don't want the lid on tightly at this point because as the fermentation process commences, the liquid may overflow from the jars.
Place the jars on a plate or tea towel on your kitchen counter to catch any potential overflow.
Leave the jars at room temperature, out of direct sunlight, for a couple of days (3 full days seems to work best in my experience). During this period, remove the lids from the jars at least once a day and make sure that the cabbage is still submerged in the brine adding more brine if necessary.
Are you seeing bubbles on top? If you are, that's a good thing! It means that your red cabbage kraut is starting to ferment.
At the end of the 3 days the fermenting kraut should start to have a fresh, clean, and slightly sour smell. You may want to do a taste test at this point but hold off on eating it for a few more days.
Now, tighten the lids and move the jars to the refrigerator. I know waiting to eat the fermenting sauerkraut can be hard but give it at least 5 more days for the flavor to develop. The longer you wait, the more flavorful it will be.