Tong sui is a sweet, warm Cantonese dessert soup that is offered in a range of flavors and textures. Literally meaning "sweet water" in Mandarin Chinese, this dessert is served as a palate-cleansing treat to cap off a meal. Just as many flavors of tong sui can be found as flavors of ice cream — perhaps even more, when varieties like red bean, black-eyed pea, glutinous rice, water chestnut and even box turtle are considered.
The base of tong sui is simple, formed by either coconut milk or water with sugar added to taste. After this mixture is brought to a boil, various chopped nuts, fruits and even vegetables like corn or water chestnuts are added. Then, the mixture simmers for about a half-hour over reduced heat. Some ingredients will take more or less time to cook, so cooks will often add them to the simmering liquid in the order it takes for them to cook. This minimizes the chance for over- or undercooked components in the final dish.
Depending on the fruits and vegetables added, tong sui takes on a myriad of colors and appearances. Some make simple mango, pearl tapioca or vanilla bean varieties that have one primary flavor; others combine several ingredients in coconut milk. One popular recipe combines the Asian fruit longan with dates, nuts, beans and snow fungus for a diverse culinary experience. Another is a medley of berries and citrus rinds imparted with the inherent creaminess of the soup.
On an international scale, some tong sui varieties are more palatable than others. The cornerstone of Hasma, for instance, is frog fallopian tubes. The Guilinggao variety of tong sui is made with box turtle. Many of the others, however, include ingredients more accepted by a world audience.
One popular ingredient used in many tong sui recipes is black sesame paste — a distinctive sweet and nutty addition, which also gives the soup a darkened hue. Seasonal fruits, vegetables and beans are customary, leading to an ever-changing variety of dessert soups. Though most prevalent in Cantonese regions of China, sweet soup stands and shops have sprung up in other parts of the world, including the United States and Europe, which boast heavy Chinese populations, especially in major cities like New York and San Francisco. These shops either make ton sui exclusively or include it among other menu items.