⭐ Buttermilk (thickened with flour or cornstarch) (Best Fat-Free Option)
3/4 cup buttermilk + 1 tbsp flour or cornstarch per 1 cup sour cream Quick tip: Thicken buttermilk to approximate sour cream’s consistency; it adds tang and moisture but may slightly alter dough hydration.
Buttermilk provides the acidity and moisture that sour cream contributes, which is important for gluten development and flavor in bagels. However, its thin consistency requires thickening with a small amount of flour or cornstarch to avoid overly wet dough.
Mix buttermilk with flour or cornstarch and let it rest to thicken before adding to the dough. Adjust other liquids slightly to maintain dough consistency.
Bagels made with this substitute have a tangy flavor but may be slightly less rich and have a marginally different crumb texture due to the lower fat content.