Acids and Bases in Cooking: From Ceviche to Baking Soda

Every time you squeeze lemon juice onto fish, add vinegar to a braise, or reach for baking soda instead of baking powder, you’re adjusting the pH of your food. Most of us do this on instinct. But once you understand what pH actually changes about food chemistry, you can do it on purpose and get much more predictable results.

What pH Is

pH stands for “potential of hydrogen” and measures how acidic or basic (alkaline) a solution is. The scale runs from 0 to 14.

pH 7 is neutral (pure water)
Below 7 is acidic (more hydrogen ions)
Above 7 is basic or alkaline (fewer hydrogen ions)

Each step on the scale represents a tenfold difference. So pH 4 is 10 times more acidic than pH 5, and 100 times more acidic than pH 6. This is why small differences in pH have large effects on chemistry.

Here’s a quick reference for common kitchen ingredients:

Lemon juice: pH 2-2.5
Vinegar: pH 2.4-3.4
Yogurt: pH 4-4.5
Buttermilk: pH 4.5-5
Coffee: pH 5
Milk: pH 6.5-6.8
Water: pH 7
Baking soda solution: pH 8.3
Egg whites: pH 7.6-8

Common Acids in Cooking

Your kitchen has several organic acids, each with a slightly different flavor profile and behavior.

Citric acid: Found in citrus fruits. Bright, clean sourness. Used extensively in lemon juice and lime juice, and as a preservative and flavor additive in processed foods. Effective at chelating (binding) metal ions, which is why lemon juice prevents cut fruit from browning. It grabs the copper and iron ions that catalyze enzymatic browning.

Acetic acid: Vinegar in any form. Sharper, more pungent than citric acid. The acetate ions in vinegar can penetrate food quickly, which is why vinegar-based quick pickles work faster than lacto-fermented pickles.

Tartaric acid: Found in grapes and wine. Less common in home cooking, though cream of tartar (potassium bitartrate, a salt of tartaric acid) is used to stabilize whipped egg whites and prevent sugar crystallization.

Lactic acid: Produced by bacteria in fermented dairy and vegetables (see the fermentation basics article). Milder, rounder sourness than acetic acid. The dominant acid in yogurt, buttermilk, and sauerkraut.

Phosphoric acid: The acid in cola drinks. You don’t cook with it, but it’s responsible for the distinctly sharp acid note in dark sodas, different from citric acid.

What Acids Do to Food

Protein Denaturation: Ceviche and Acid Marination

Ceviche is the classic demonstration. Raw fish or shrimp sits in lime or lemon juice for 15-30 minutes. The acid denatures the proteins, unfolding their 3D structure and causing them to firm up and turn opaque, much like heat would. The fish looks and somewhat feels “cooked” because the protein structure has changed.

This is also why acid marinades tenderize meat, but only to a point. Acid denatures the surface proteins, breaking down some of the connective tissue. If you marinate too long in a highly acidic marinade, though, the proteins over-denature and become mushy rather than tender. There’s a sweet spot, usually 30 minutes to 4 hours depending on the cut and acid concentration.

Acid denaturation in ceviche does not kill all pathogens the way heat does. For immunocompromised individuals or when using high-risk seafood, heat is the only reliable safety step.

Color Changes in Vegetables

This is where pH gets visually dramatic.

Red/purple vegetables (red cabbage, red onion, radicchio, beets) get their color from pigments called anthocyanins. These pigments are pH indicators. They change color depending on acidity.

In acidic conditions (low pH): bright red or purple
In neutral conditions: purple to blue-purple
In alkaline conditions: blue, then green, then yellow

Add a splash of vinegar or lemon juice to red cabbage while cooking and it stays vibrantly purple. Cook it in tap water (often slightly alkaline) and it drifts toward blue-grey. This isn’t just aesthetics. The same anthocyanin chemistry is why red cabbage soup looks different every time depending on your water’s mineral content.

Green vegetables (broccoli, green beans, peas) stay green thanks to chlorophyll. Acid turns chlorophyll olive-drab brown by displacing the magnesium ion at the center of the chlorophyll molecule. This is why you don’t add lemon juice to vegetables while they’re cooking. Add it after cooking and just before serving if you want brightness without color loss.

Alkalinity has the opposite effect on green vegetables: it keeps them vivid green longer by preventing chlorophyll degradation. Some old-school recipes call for adding baking soda to boiling water to keep vegetables green. It works. It also turns the vegetables mushy and destroys water-soluble vitamins. It’s not recommended.

Preservation

Acid preserves food primarily through pH reduction. Most pathogens, including Listeria, E. coli, and Salmonella, can’t survive below pH 4. Pickling (whether quick vinegar pickling or fermentation) works by getting food below this threshold. This is also the principle behind canning safety. High-acid foods (tomatoes, fruit) can be safely processed in a water bath canner because their pH already inhibits botulism. Low-acid foods require pressure canning to reach temperatures high enough to sterilize without relying on pH.

Common Bases in Cooking

Baking Soda

Baking soda is pure sodium bicarbonate (NaHCO3). It’s a weak base with a pH around 8.3 in solution.

When baking soda contacts any acid (buttermilk, lemon juice, yogurt, vinegar, brown sugar, cocoa powder, molasses) a chemical reaction produces CO2 gas. That CO2 leavens baked goods by expanding existing air bubbles in the batter.

The reaction happens fast. Once baking soda meets acid and moisture, bubbles start immediately. This is why pancake batter or muffin batter mixed with baking soda should go into a hot pan or oven quickly. You’re already spending your leavening.

Baking soda also neutralizes excess acid in the recipe, affecting flavor. A recipe using only baking soda (with an acidic ingredient) will taste relatively neutral or slightly alkaline.

Baking Powder

Baking powder is a mixture: typically baking soda (base), cream of tartar or sodium aluminum sulfate (acid), and cornstarch (to absorb moisture and prevent premature reaction).

Because baking powder contains its own acid, it doesn’t require acid in the recipe to produce CO2. It releases gas in two stages: once when it contacts moisture, and again when heated. This “double-acting” behavior gives recipes more flexibility. The batter can sit for a bit and still rise in the oven.

Use baking soda when the recipe has enough acid to react with it. Use baking powder when the recipe doesn’t have significant acid.

Some recipes use both. This typically means the recipe needs more leavening than baking powder alone can provide, or the baker wants to neutralize some acid for flavor reasons while still having plenty of CO2 for lift.

The lye exception: Pretzels and some bagels use a food-grade lye (sodium hydroxide) wash before baking. Lye is a strong base (pH close to 14). It reacts with proteins on the surface of the dough to form new compounds that give the pretzel its distinctive deep brown color and chewy exterior. This is not something to try casually at home. Food-grade lye requires careful handling.

How pH Affects Browning

pH directly affects the rate of the Maillard reaction. This relationship is underappreciated by most cooks.

The Maillard reaction proceeds faster under alkaline conditions and slower under acidic conditions. The reaction requires that an amino group on an amino acid interacts with a reducing sugar. At higher pH, more of those amino groups are in the reactive (unprotonated) form.

In practical terms:

A small amount of baking soda added to caramelizing onions dramatically speeds up browning. Many cooks add a pinch (1/8 teaspoon for a large pan of onions) when they want to shortcut the 45-minute process.
Chocolate cake recipes often include baking soda partly for leavening but partly to raise pH and promote browning in cocoa. Dutch-process cocoa has been alkalized for similar reasons. It’s darker and has a different flavor than natural cocoa.
Adding acid (like tomatoes) to braised meat early can slow surface browning. Professional cooks often sear before adding acidic liquids.
The distinctive dark color and flavor of pretzels from the lye wash is an extreme version of this. A very high-pH environment creates rapid, deep Maillard browning during baking.

Deep dive: Why buttermilk and baking soda make fluffier pancakes than milk and baking powder

This seems like a substitution question, but the answer reveals something interesting about baking chemistry.

Buttermilk is acidic (pH around 4.5-5.0) and contains lactic acid from bacterial fermentation. When you combine buttermilk with baking soda, several things happen:

The acid-base reaction produces CO2 immediately, giving the batter lift right away
The sodium bicarbonate neutralizes some of the acidity, reducing the sour flavor and leaving a slight alkalinity
That slight alkalinity enhances Maillard browning, giving the pancakes a slightly deeper color and more complex flavor
Buttermilk’s acidity also partially denatures the gluten proteins, resulting in a more tender crumb

When you use milk (pH ~6.7) and baking powder instead, you get CO2 from the double-acting reaction and adequate leavening, but you don’t get the flavor complexity, the tenderness from acid denaturation of gluten, or the enhanced browning.

The textural difference comes down to gluten. Acid weakens gluten networks slightly by disrupting some of the protein-protein interactions. This makes buttermilk pancakes more tender and delicate compared to the slightly chewier result from a neutral batter. For pancakes, tender is almost always the goal.

This same logic applies to other quick breads. Buttermilk biscuits, banana bread with yogurt, lemon loaf. All of these use an acidic dairy product to tenderize gluten while baking soda provides the lift. The chemistry is consistent: acid plus base plus heat equals something more than the sum of its parts.