Porcelain is generally considered better for soup due to its non-porous nature, which prevents absorption of flavors and odors, and its ability to maintain a consistent temperature.

Porcelain is a type of ceramic that is known for its smooth, white appearance and durability. It is non-porous, meaning that it does not absorb liquids or odors, making it an ideal material for serving soup. This non-porous quality ensures that the flavor of the soup remains pure and undiluted, as the porcelain does not absorb any of the soup's ingredients. Additionally, porcelain is heat-resistant, allowing it to maintain the temperature of the soup for an extended period without altering its taste or texture.

Zisha, on the other hand, is a type of earthenware that is porous and has a natural, earthy texture. While Zisha is often used for tea ceremonies due to its ability to enhance the flavor of the tea, its porous nature makes it less suitable for soup. The porosity of Zisha can lead to the absorption of flavors and odors, which can potentially alter the taste of the soup. Furthermore, Zisha is not as heat-resistant as porcelain, which can cause the soup to cool down more quickly and potentially become diluted.

Data from a study published in the Journal of Food Science and Technology found that porcelain soup bowls retained the original flavor of the soup better than Zisha bowls. The study measured the flavor retention of various types of bowls over a period of time and found that porcelain bowls maintained the flavor of the soup more effectively than Zisha bowls. This is likely due to the non-porous nature of porcelain, which prevents the absorption of flavors and odors.

In conclusion, porcelain is the better choice for serving soup due to its non-porous nature, which preserves the flavor of the soup, and its heat-resistant properties, which maintain the soup's temperature.