Once your napa cabbage has been brined to perfection, drain and rinse 2-3 times to wash off any excess salt. Drain off any excess water and add cabbage into a large bowl.
Pour over kimchi sauce and mix thoroughly. (I highly recommend wearing some gloves)
Add kimchi into a clean airtight container of choice. I recommend using a kimchi fermentation container (you can order them online or find them at most Korean grocery stores). The next best option would be to use 3 - 1 quart size mason jars with the wide mouth. Once you have gotten all the kimchi into your container, press the kimchi down to submerge all the cabbage under the kimchi sauce and close the lid. If you have a kimchi fermentation container, you can press out all the air with the airtight piece, then pop the lid on. Lactobacillus grows best in anaerobic conditions, meaning in low-oxygen conditions. Thus, kimchi is fermented in a closed container to keep air out.
Set aside in a cool place away from direct sunlight. Keep at room temperature for 1-3 days. Times will vary depending on the temperature of the room. On a hot day, it can take less than 1 day. On a normal day, it can take about 2 days. On a cool winter day, it can take up to about 3 days. These are general estimated times.
Put your kimchi in the refrigerator when it reaches about 60-70% of the desired sourness. Your kimchi will continue to develop flavor and sourness in the fridge. You can eat this right away, but it’s best about 1-2 weeks after it’s been in the fridge. This gives the bacteria more time to develop depth of flavor. Do not leave out kimchi at room temperature for too long because that will result in a mushy kimchi that’s overly sour. Do not keep opening the container multiple times per day and exposing the bacteria to oxygen. This will disrupt the Lactobacillus and result in a bad tasting kimchi. Try to check it once per day only. Creating the ideal environment for the bacteria is the key to developing the best flavor and texture for your kimchi.