Year of Plenty fermentation products are designed to enhance your life by helping you prepare and preserve the fruits of your labor. Lacto-fermentation is an natural method of food preservation resulting in delicious food with well-documented health benefits. Year of Plenty fermentation lids are specifically designed to aid in the fermentation process by allowing gas bubbles to escape from the brine while preventing oxygen from entering the jar. Oxygen causes mold - you don't want that, so use the lids. You will be making your first batch of sauerkraut within a few minutes of opening the package. Happy Fermenting!