Vinaigrettes are technically temporary emulsions, meaning while you can whisk them together, they'll separate eventually. But not to worry, you can give them a good shake or whisk to mix them together again before using. Standard store-bought salad dressings are usually made with some sort of additives or emulsifying agents to keep the vinaigrette from separating. These healthy homemade salad dressings don't have these add-ins, so it's normal for them to separate.