Condensation inside your fermentation jars is perfectly normal and indicates that fermentation is actively occurring. It's a sign that your vegetables are releasing moisture and gases as they ferment.
During fermentation, microorganisms like bacteria and yeast consume sugars and other compounds in your vegetables. This process produces various byproducts, including carbon dioxide and water vapor. The water vapor evaporates from the fermenting vegetables and rises within the jar. When this warm, moist air comes into contact with the cooler surfaces of the jar's lid and walls, it condenses back into liquid water, forming the droplets you observe. The amount of condensation can vary depending on factors like the ambient temperature, the type of vegetables being fermented, and the activity level of the microorganisms. A higher temperature generally leads to more condensation. The presence of condensation is a good indicator that your fermentation is progressing as expected.
While condensation is normal, excessive condensation combined with other signs like mold growth could indicate a problem. Ensure your vegetables are fully submerged in brine to prevent unwanted mold or yeast from developing on the surface.