Buttermilk's Primary Reaction: The Leavening Effect
The most common and important reaction buttermilk undergoes is with baking soda. Buttermilk is a mildly acidic ingredient, and baking soda is a pure alkaline base. When they combine, they neutralize each other, and this acid-base reaction releases carbon dioxide gas. This gas becomes trapped in the batter or dough, forming bubbles that expand when heated in the oven. This is the secret behind light, fluffy pancakes, tender biscuits, and airy cakes.
The Role of Temperature in the Leavening Reaction
While the initial reaction between buttermilk and baking soda begins at room temperature, it is significantly amplified by the heat of the oven. The rising temperature causes the trapped carbon dioxide bubbles to expand rapidly, providing the final and most powerful 'lift' to your baked goods. This two-stage process—initial reaction and heat-driven expansion—is why buttermilk and baking soda are such a powerful leavening pair in quick breads and other recipes.
Buttermilk's Secondary Reaction: The Tenderizing Effect
Beyond its leavening power, buttermilk's acidity also reacts with proteins. This property makes it an excellent marinade for meat, especially poultry. The lactic acid in buttermilk helps to break down tough muscle fibers and collagen in the meat, resulting in a more tender and juicy final product. Unlike harsher acids like vinegar or citrus juice, buttermilk's milder acidity prevents the meat from becoming tough or stringy. This reaction is the reason behind the incredibly moist and flavorful buttermilk fried chicken.
Buttermilk and Other Ingredients
Baking Powder
Buttermilk reacts differently with baking powder. Baking powder is a mixture of baking soda, a powdered acid, and a starch. Since it already contains an acid, buttermilk can actually interfere with the leavening process, potentially reducing the amount of carbon dioxide released. For recipes that use buttermilk, it is often necessary to reduce the amount of baking powder and add a small amount of baking soda to achieve the best results. This highlights the importance of recipe-specific instructions when using these leavening agents.
Gluten in Flour
The acid in buttermilk also reacts with gluten, the protein network that develops in flour-based doughs. Buttermilk's acidity helps to break down the long strands of gluten, resulting in a more tender and softer crumb in baked goods. This is particularly beneficial in recipes like biscuits and scones, where a tender, pillowy texture is desired over a chewy one. This reaction explains why many baked goods made with buttermilk have a distinctly soft and delicate texture.
Comparison: Buttermilk's Reactions vs. Regular Milk's
| Feature | Buttermilk Reactions | Regular Milk Reactions |
|---|---|---|
| Primary Leavening | Reacts with baking soda to produce carbon dioxide gas, providing significant lift. | No significant reaction with baking soda; does not provide leavening on its own. |
| Protein Tenderizing | Acidic properties break down tough meat proteins, resulting in a more tender product. | Not acidic; does not break down or tenderize meat proteins. |
| Flavor Profile | Adds a tangy, slightly sour flavor to dishes, which can add complexity. | Adds a creamy, neutral flavor; does not alter the overall taste significantly. |
| Gluten Structure | Acid reacts with gluten, leading to a softer, more tender crumb in baked goods. | Helps activate gluten, but without the acid, it doesn't have the same tenderizing effect. |
| Metal Interaction | Reacts with copper and brass, forming toxic compounds and spoiling the product. | Does not react with these metals in the same harmful way. |
Buttermilk's Reaction with Metals: A Cautionary Tale
Because buttermilk contains lactic acid, it is a bad idea to store it in containers made of reactive metals like copper or brass. The acid will react with the metal, forming poisonous metallic salts that can cause food poisoning and spoil the buttermilk. For this reason, buttermilk and other acidic dairy products should always be stored in non-reactive containers made of materials like glass, plastic, or stainless steel.
Conclusion
Understanding what does buttermilk react with is key to mastering its use in the kitchen. Its most well-known reaction is with baking soda, creating a powerful leavening effect for fluffy and tender baked goods. The same acidity that drives this reaction also makes buttermilk an exceptional meat tenderizer for marinades. However, this same acidic property also warns us to be cautious about storage, as it can react harmfully with certain metals. By respecting the simple chemistry of buttermilk, home cooks can unlock its full potential to create delicious, high-quality dishes every time. For more in-depth information on food chemistry, a wealth of resources is available online, such as the informational site of the Australian Academy of Science which touches on the science behind foods like pancakes made with buttermilk.
