Causes of Foam on Pickled Eggplant

Using inappropriate salt can cause pickled eggplant to develop foam. When pickling eggplant, it’s essential to use coarse salt (sea salt). This type of salt is obtained through the evaporation of seawater. The remaining salt crystals are cleaned but not fully refined, so they retain many trace minerals such as iron, zinc, sulfate, carbonate, potassium, magnesium, and calcium. Sea salt contains about 80% sodium chloride (NaCl) and has a mild sweet aftertaste, with mineral and iron notes.

In contrast, refined salt is sea salt that has been fully processed, removing all trace minerals, so it contains 97–99% sodium chloride. This type of salt tastes much saltier and lacks the natural aftertaste.

Additionally, refined salt may be iodized. Other additives can include anti-caking agents to prevent clumping, and sometimes dextrose, which helps stabilize the iodine. Using refined salt for pickling cucumbers or eggplants can cause discoloration and foaming.

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Choose Fresh Eggplants

Eggplants can be divided into two types: white-skinned and green-skinned (also called turmeric-type eggplant with slightly green skin). You can choose the type based on your preference.

Turmeric-type eggplants have fewer seeds and thicker flesh. They are suitable for quick pickling or pressed pickles. When pickled, the eggplant turns yellow. It’s best to choose medium-sized eggplants—not too young, not too old.

Fresh eggplants should be lightly sun-dried to remove some moisture, which helps maintain a crisp texture during pickling.

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Soak and Wash the Eggplants

Remove the stems of the eggplants but do not cut too deeply. Simply remove the stem while keeping the flesh intact. After cutting, immediately soak the eggplants in water to prevent browning. Then rinse with clean water and toss with coarse salt. Salting helps draw out water, making the eggplants crisper, and also has antibacterial effects to prevent spoilage and foaming.

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Prepare the Pickling Brine

You will need a small amount of peeled and sliced garlic, and thinly sliced galangal (or ginger). You can also add sliced chili if you want a spicy flavor.

For the brine, use boiled water cooled to room temperature. Mix 1 liter of water with 50 grams of coarse salt. You can boil the water and salt together, but be sure the brine is completely cooled before using it to pickle the eggplants.

To speed up fermentation, you can add a little sugar to the brine.

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Pickling the Eggplants

It’s best to use ceramic, porcelain, or glass jars for pickling. Wash the jar thoroughly and rinse with boiling water to sterilize. Make sure the jar is completely dry before use.

Remove the salted eggplants, rinse with clean water, and let them drain. Layer the eggplants with galangal, garlic, and chili. Pour the prepared brine over the eggplants until fully submerged.

Use a bamboo mat or a plate to press down so that all the eggplants remain underwater. This ensures even pickling, prevents browning, and avoids foam formation.

After 2–3 days, the eggplants will turn yellow and develop a sour taste, indicating they are ready to eat. Fermentation time may vary depending on the weather. Store pickled eggplants in a cool, dry place. In hot weather, you can refrigerate them to slow fermentation. Always use clean spoons or chopsticks to serve, minimizing bacterial contamination that could spoil the entire jar.