Combining soy sauce and milk can result in a peculiar flavor combination that may not be appealing to everyone. While there's no inherent danger or safety issue in mixing soy sauce and milk, it's essential to consider the taste and texture implications.
Soy sauce is a savory, salty, and umami-rich condiment commonly used in Asian cuisine. On the other hand, milk is creamy and has a mild, sweet flavor. When boiled together, the contrasting flavors can clash, leading to an odd taste profile that may not be enjoyable.
Additionally, the acidity in soy sauce can curdle the proteins in the milk when exposed to high heat or acidity for an extended period, resulting in an undesirable texture. This is similar to what happens when you add lemon juice or vinegar to milk, causing it to curdle.
However, if you wish to experiment with unique flavor combinations, you can try small amounts of soy sauce and milk in a separate and controlled setting before incorporating them into a larger dish. Some cuisines do use soy sauce in combination with dairy or dairy-like ingredients, such as in certain fusion recipes or sauces, but these are generally used in specific ways to balance flavors.
If you want to create a sauce that incorporates both soy sauce and milk, it's better to do so gradually, adjusting the ratios and tasting as you go to find a balance that suits your palate. Remember that cooking is all about experimentation, and sometimes unexpected flavor combinations can turn into delightful surprises.
Alternatively, you can explore other umami-rich ingredients to complement the milk in your dish without clashing flavors, such as using fish sauce, miso paste, or mushrooms, which can provide depth and richness without creating a jarring taste.