Why are thermoses not suitable for acidic drinks?

Thermos are an indispensable drinking device in our daily lives, but many people may have heard that “acidic beverages like carbonated drinks and milk shouldn’t be stored in thermoses.” Is this a myth or scientific fact? Today, we’ll delve into the compatibility of thermoses with acidic substances from the perspectives of material properties, chemical reactions, and practical safety.

1. Carbonated Beverages: Not Just Leakage, but Potential Explosion

Bebidas carbonatadas (such as cola and Sprite) contain large amounts of carbon dioxide gas. Thermos seals primarily rely on silicone seals. While these effectively prevent leakage of ordinary liquids, they can’t completely block gas permeation. Especially when shaken or bumpy, the increased gas pressure in the beverage can cause the following:

• Liquid Leakage: Gas continuously escapes, pushing the beverage out of the rim or cracks, soaking bags or clothing.
• Surge in Pressure Within the Cup: If the thermos seal is extremely tight, gas can’t be released in time. The continued buildup of pressure can even cause the cup to burst, posing a safety hazard.

2. Acidic substances: Corrode aço inoxidável, affecting health and insulation performance.

The inner liner of a thermos is typically made of 304 ou 316 aço inoxidável. While these materials are corrosion-resistant, prolonged contact with acidic substances (such as juice, lemonade, and milk) can still cause chemical reactions:

• Metal ion precipitation: An acidic environment slowly corrodes stainless steel, potentially leaching trace amounts of metal elements like chromium and nickel. Long-term consumption can be harmful to health.
• Oxidation and Rust: Acidic substances can damage the passive film on the stainless steel surface, accelerating oxidation and causing rust spots on the inner liner. This not only affects the appearance but also shortens the lifespan of the thermos.
• Beverage Deterioration: Protein-rich beverages like milk and soy milk stored in a thermos for extended periods can easily breed bacteria, causing deterioration, sourness, and even gastrointestinal discomfort.

3. Usage Tips: How to Use a Thermos Properly?

Although thermoses aren’t suitable for storing acidic beverages long-term, occasional use is fine. Just be mindful of the following:

• Cleaning promptly: After using acidic beverages, be sure to thoroughly clean them with a neutral detergent to avoid residue.
• Avoid prolonged storage: Drinks like milk and juice should be consumed within two hours and not stored overnight.
• Choose a dedicated cup type: If you need to carry carbonated beverages, it’s recommended to use a sports bottle with a venting feature rather than a tightly sealed thermos.

Safe Use and Extended Lifespan

The thermos’ material and design make them ideal for storing neutral liquids such as hot water and tea. Carbonated and acidic beverages can not only leak and burst, but can also corrode the cup, potentially affecting your health. Therefore, proper use of the thermos will ensure it lasts longer.