What Foods React With Copper and Why You Should Care

December 2, 2025 •

4 min read

According to the U.S. FDA, foods with a pH less than 6.0 should not come into contact with copper materials, as it can cause the metal to leach into the food. Understanding exactly what foods react with copper is crucial for home cooks, particularly those using unlined vintage pots or decorative pieces. This reactivity can alter food taste and pose significant health risks if proper precautions are not taken.

Quick Summary

Acidic ingredients like tomatoes, vinegar, and citrus cause copper ions to leach into food, which can lead to toxicity symptoms. Modern lined cookware is safe, but unlined copper must be used carefully for specific tasks like whipping egg whites or making jams to avoid contamination.

Key Points

Acidic Foods React Strongly: Foods with a pH below 6.0, such as tomatoes, citrus, and vinegar, react with unlined copper, causing metal ions to leach into the food.
Copper Toxicity is a Risk: Ingesting high levels of leached copper can lead to symptoms like nausea, vomiting, abdominal pain, and diarrhea.
Lined Cookware is Safe: Modern copper pots and pans are lined with a non-reactive metal like stainless steel or tin to create a protective barrier.
Unlined Copper Has Specific Uses: Unlined copper is safe and even beneficial for tasks involving sugar (jams, candy) and whipping egg whites due to controlled chemical reactions.
Inspect Vintage Items: Always check vintage or heirloom copper for corrosion or exposed patches, as these are unsafe for cooking.
Avoid Prolonged Food Storage: Never store leftover food, especially acidic dishes, in copper containers, as this increases the risk of contamination.
Temperature Increases Reactivity: Higher temperatures accelerate the reaction between copper and acidic foods, increasing the rate of metal leaching.

The Core Reaction: Acids and Copper

The most significant and common reaction that occurs with copper and food involves acidic ingredients. Copper is a reactive metal, and when it comes into contact with an acid, a chemical reaction occurs. This process causes copper ions to dissolve and leach into the food, contaminating it. This can cause the food to take on an unpleasant metallic taste and, in large enough doses, can be toxic. The risk is highest with unlined or corroded copper cookware where there is no protective barrier between the food and the metal.

Why Acids Are the Main Culprit

Foods with a low pH are the primary catalysts for this reaction. The higher the acidity, the more vigorous the reaction and the greater the risk of copper leaching. Common acidic foods found in many kitchens include:

Tomatoes: The high acidity in tomatoes makes them one of the most reactive foods with unlined copper. Simmering a tomato sauce for a long period in an unlined pot is particularly hazardous.
Citrus Fruits: Lemon, lime, and orange juice are highly acidic and should never be cooked or stored in unlined copper containers.
Vinegar: Whether in dressings or reductions, vinegar's acetic acid content will react strongly with copper.
Wine: The acids in wine can cause a similar reaction, so avoid deglazing an unlined copper pan with wine.
Pickles: The brine in pickled foods is acidic and can cause copper containers to tarnish and react.

Surprising Exceptions: The Safe Reactions

Not all copper reactions are hazardous. In fact, some unlined copperware is intentionally used for specific culinary tasks where a controlled reaction is beneficial.

The Sweet Science of Sugar

Traditional French confectionery often uses unlined copper pots for making jams, caramels, and candy. The reason for this is twofold. First, copper's superior heat conductivity allows for very precise temperature control, which is essential for sugar work. Second, the high sugar content in these recipes buffers the acids in the fruit, preventing a negative reaction. Additionally, copper ions can bind with pectin, helping jams to set more effectively. The key is to avoid letting the jam or candy sit in the pot for too long after cooking.

The Magic of Whipped Egg Whites

Whipping egg whites in an unlined copper bowl is a long-held secret of pastry chefs for creating a more stable, voluminous foam. As the egg whites are whipped, copper ions from the bowl are absorbed by a protein called ovotransferrin. This prevents sulfur atoms from bonding too tightly, which would cause the foam to collapse. The result is a glossy, stable meringue that is more difficult to overmix.

Beyond Acids: Other Noteworthy Reactions

While acids are the primary concern, other foods can also react under certain conditions. For instance, a study found that highly alkaline egg whites can cause severe corrosion of copper, suggesting a complex interaction with certain proteins. Some sources also recommend caution with storing milk in copper, as its enzymes may react, though modern linings mitigate this risk. Cooking with high-fat or certain dark vegetables like spinach in unlined copper has also been cautioned against due to potential interactions, though the evidence is less conclusive than with acids.

Comparison of Copper Cookware


Feature	Lined Copper Cookware (e.g., Stainless Steel)	Unlined Copper Cookware
Safety	Completely safe for all food types, including acidic foods.	Potentially toxic when used with acidic, alkaline, or salty foods.
Food Compatibility	Suitable for all cooking tasks, from searing meat to simmering sauces.	Limited to specific tasks like whipping egg whites or making sugar-based confections.
Maintenance	Easier to clean and more durable. Lining protects the copper interior.	Requires careful cleaning to avoid scratching the lining (if present) or damaging the copper.
Heat Control	Retains the excellent heat conductivity of copper but can have slightly slower response times due to the lining.	Offers the fastest heat response, ideal for delicate temperature-sensitive cooking.

What Are the Risks of Copper Exposure?

Ingesting excess copper from a contaminated meal can lead to acute copper toxicity, a form of food poisoning. Symptoms can include nausea, vomiting, abdominal pain, and diarrhea. In rare cases of chronic high-level exposure, such as from consistently using damaged unlined cookware, more severe issues like liver or kidney damage can occur. The risk is generally low with modern, properly maintained cookware, but it is a serious concern with vintage, unlined, or corroded pieces.

How to Ensure Safe Cooking with Copper Cookware

To enjoy the aesthetic and thermal benefits of copper without the risks, follow these safety guidelines:

Use lined cookware: Always opt for copper pots and pans with a protective lining, such as stainless steel or tin, for general cooking.
Inspect vintage pieces: If you have vintage copperware, check the interior carefully for scratches, flaking, or exposed copper, especially if it was originally tin-lined. If the lining is compromised, it is no longer safe for cooking.
Reserve unlined pieces: Dedicate unlined copper bowls or pots exclusively for safe applications like whipping egg whites or candy making.
Avoid storage: Never store acidic foods like tomato sauce or fruit compote in any copper container, even briefly.
Hand wash gently: Use soft utensils and hand wash your copperware to avoid scratching the protective lining.

Conclusion: Know Your Cookware

While copper is a beautiful and effective material for cooking, its reactivity demands careful handling. Knowing what foods react with copper, particularly acidic ones, is the key to preventing potential health risks and metallic-tasting food. For everyday cooking, relying on modern, lined copper is the safest choice, while unlined copperware should be reserved for its specific, time-honored uses. Ultimately, understanding your kitchen tools and their material properties is essential for both food safety and achieving culinary excellence. For more information on copper safety, consult resources from the Agency for Toxic Substances and Disease Registry.

Frequently Asked Questions

You can only cook tomato sauce in a copper pot if it is lined with a non-reactive metal like stainless steel or tin. Cooking acidic tomatoes in unlined copper will cause copper ions to leach into the food, which is a health risk.

The safest type of copper cookware is modern, lined cookware, most often with a stainless steel interior. The lining provides a durable, non-reactive barrier that prevents food from touching the copper.

Unlined copper pots are used for jams and candy because sugar acts as a buffer against the acids in fruit, preventing a negative reaction. The high thermal conductivity is also beneficial for precise temperature control required in sugar work.

Symptoms of acute copper toxicity can include nausea, vomiting, abdominal pain, and diarrhea. Chronic exposure from contaminated water or food can also lead to more severe issues like liver and kidney damage.

Yes, it is safe to whip egg whites in an unlined copper bowl. The copper ions stabilize the protein structure of the egg whites, resulting in a more stable, voluminous foam.

You should not use unlined copper pots or bowls for serving food, especially if the food is acidic or salty, as it can still react with the metal and contaminate the meal.

Inspect the interior of your pot. If it shows any signs of scratching, peeling, or corrosion that exposes the underlying copper, it is not safe for cooking acidic foods. It is safest to use such pots only for non-reactive tasks or for decoration.