Taking out of the barrel: when ready to use fermented cabbage, take the lid off the barrel, remove heavy objects, and take out however many cabbage heads as you'll need. Transfer them to a deep bowl immediately as they'll be dripping with kraut juice (rasol). Also, take as much kraut juice as you need as well, or use whatever drips out of the cabbage heads (they hold a lot of it). Transfer the juice to a bottle and keep it in the fridge. After you're done taking what you need out of the barrel, return the weight(s) on top, and fasten the lid.
Serving and/ or using fermented cabbage for a dish: before you use sour cabbage, taste it. If it's too salty for your taste, wash it out under lukewarm water. Remove outer 1-2 leaves, and use the rest for your chosen dish.
If you have leftover fermented cabbage, place it in an airtight container and keep it in the fridge for up to 2-3 days. Kiseli kupus smell packs a punch, so be warned!
Freezing fermented cabbage: freeze whole heads (if you have a big freezer) in a freezer bag for up to 6 months. However, if you plan to use sour cabbage for salads only, shred or grate a desired amount, put them in the freezer bags, and transfer them to the freezer for up to 6 months. Finally, if freezing to use in sour cabbage rolls (sarma), freeze whole leaves. Simply remove leaves from a cabbage head, stack them in piles of 5-10, and then roll the stacks up. Place rolls in a freezer bag. Transfer to the freezer for up to 6 months.
Thawing fermented cabbage: a few hours before you plan to use it, take it out and let it thaw at room temperature. Use it for the recipe. Keep leftovers in the fridge in an airtight container or a freezer bag.