Adding milk to mashed potatoes isn't just for flavor, but for structure, as well. As Harold McGee, author of "On Food and Cooking," explains, when potatoes are cooked, the cells swell and separate, creating a dry and fluffy texture. By coating the pieces with liquid and fat, the potato comes together to create the smooth mashed potatoes much loved as a side dish. Whether you simply ran out of milk, cannot consume dairy for health or personal reasons, or, you are looking to try something new, many substitutes exist for milk in mashed potatoes.
If dairy consumption is not a problem, try substituting all or part of the milk with cream. Half-and-half, light and heavy cream all work, though the higher the fat content, the more prominent the flavor. Start with one-quarter of the amount of milk you would normally use and add the substitute gradually until you reach the desired consistency and flavor. Sour cream provides a tangy and rich alternative to milk. Add about 1/2 cup of sour cream per cup of milk in the original recipe; adjust to taste. For another tangy alternative, try substituting buttermilk at a 1-to-1 ratio. Creme fraiche, added as one cup per 3 pounds of potatoes, offers a luxurious substitute for rich mashed potatoes. Alternatively, add 1/4-cup instant nonfat dry milk plus 3/4 cup of the water the potatoes were cooked in as a substitute for each cup of milk.
If you prefer a non-dairy substitute for the milk in mashed potatoes, opt for a plant-based milk, such as soy, rice, oat, hemp or almond milk. Substitute these options at a 1-to-1 ratio. Consider adding an extra tablespoon or two of vegan butter for richer potatoes that more closely mimic the fat in milk. Each of the different substitutes brings its own flavor, and the potatoes will taste more earthy or nutty, depending on your choice. Coconut milk may also be substituted, but add a coconut flavor that might be off-putting for some palates.
Substitute chicken or vegetable stock for milk for rich mashed potatoes. Choose a strong broth with full sodium for the most flavor, preferably homemade or a high-quality brand, and substitute it at a 1-to-1 ratio. Using broth instead of milk adds the benefit of cutting fat from the dish, making it a good choice if you're watching your caloric intake.
Vary the flavor and texture of mashed potatoes by mixing and matching milk substitutes. Use both broth and cream, or add a dollop of sour cream alongside the half-and-half. Add vegetable broth and soy milk in equal parts. Try substituting creme fraiche and light cream for an over-the-top decadent side dish. Enhance any of the substitutes by adding extra flavor, such as roasted garlic or freshly chopped sage.