"Suhl-leung Tang, What makes the broth milky? Is it milk?"

In the dish Suhl-leung Tang, What makes the broth milky? Is it milk?

Thank you for the question. The color comes from the stock. The milky (more like skim milk) appearance comes from the minerals that have leached out of the bone & bone marrow during long, sustained heat source to break down the bone matrices.  As you may know, stocks are in general made from cooking bones & remnant meat pieces on the surface. The Korean stock has had a long and even spiritual history. The stocks were often made in the past centuries in the context of "BoShin". "BoShin" literally means supplementing(Bo) the body (Shin). This may be another instance where culinary creativity & ingenuity comes to the rescue in meager pickings in the kitchen. Meat has always been the most prized & costly item in most traditional cultures. Due to its high cost, poor general populace could not afford to keep meat in their diet predictably. Often, eating of beef was an annual event while celebrations with pork possibly was a semi-annual activity. Frequently, it was a wedding, 100th day birthday, 1st year birth day, 60th day birthday, each decade mark thereafter, or funerals. Chicken was less costly & was more affordable monthly culinary affair. For the most part, in traditional non-aristocrat, non-royal Korean kitchens, vegetables, beans, in-season wild items (grasshopper, frog, wild game, birds), fish, and poultry provided protein/amino acid needs. In this economic & culinary circumstances, recipes were developed to use every part of the scarce animal. Hence, are, the less frequently seen fares such as head cheese, aspics, blood sausage, pigs feet, whole pig soup, blood clot soup, vertebrae stew, cooked or (rarely) raw inner organs. Less frequently, in farming areas, fresh liver, heart, or bile from organically farm grown animals were eaten dipped in simple dipping sauce made from sesame oil or coarse salt. This type of preparations were mostly for medicinal purposes.
Traditional oriental medicine providers have always had special reverence for food items. They regard food more like daily medicine & also assign various spiritual values in the context of chi, yin & yang . In this context, when serious general weakness or an illness strikes a family member, these families were often advised to purchase large cow bones & make milky stock to "BoShin". Illness in this sense was considered a tipping point when the body can no longer compensate for the lack of supply to the rigorous nutritional needs. This "BoShin" combined with bed rest, often did the trick. Families that achieved economic independence with hard work, would often incorporate this healing cuisine into their annual periodic culinary events. The stocks were made by applying constant high heat for an extended period of time, often for days. The resultant stock was rich, more like whole milk or even cream with emulsion resulting from this cooking method. The stock contained minerals (from the bone), fat (from the bone marrow) & protein/amino acids (from the meat). The BoShin stocks were served warm, simply with coarse sea salt & neatly-sliced fresh green onion garnish. This was often a welcome relief to a diet lacking animal proteins, minerals, & fats.
The restaurant version is much leaner with fat skimmed off. One can still see the simple approach, though, from the ways Suhl-leung Tang is still served. Simple with sea salt, green onion garnish, & Kak-doo-gi on the side. Kak-doo-gi is cubed spicy radish kimchi. For this pairing, Kak-doo-gi is served generally in a pleasantly fermented stage. The acidity serves as a sort of palate cleanser in between spoonfuls of richness. Nevertheless, Suhl-leung Tang has its own story to tell as well. It involves a king. So, stay tuned!
Anyhow, the tradition of BoShin concept still permeates the Korean culinary culture. Even today with economic affluence in the country, people are observed purchasing large pieces of bone as a gift to their aging parents or unwell family members for BoShin. However, Korean kitchen is in constant transition. Back, is the ingenuity that incorporated this poorly accommodating ingredient into its culinary repertoire. It is hard at work, making positive changes to accommodate needs in the time of bounty.