Thermoses are indispensable allies to keep our drinks hot or cold for longer. They are practical, durable, and increasingly popular for taking coffee, tea, or water anywhere. However, not everything is suitable to be stored in a thermos.

Some liquids or foods can spoil it, alter the taste, or even affect your health. In this article we tell you what are the three things that you should never put inside your thermos and how to take care of it correctly so that it lasts for many years.

The 3 things you should never store in a thermos flask

1. Dairy drinks (milk or derivatives)

Storing hot milk or milk drinks in a thermos may seem like a good idea, but it’s a serious mistake. Milk is a highly perishable product that, when kept at a constant temperature for several hours, favors the proliferation of bacteria. This can not only cause a bad odor, but also health risks if consumed later. In addition, residue can stick to the interior and be very difficult to clean completely.

Advice: If you need to carry milk, try to use a thermal container only for a short time and wash it as soon as you finish using it.

2. Natural juices or acidic drinks (lemon, orange, etc.)

Liquids with a high acid content, such as citrus juices, can react with stainless steel or other materials in the thermos, causing wear, alteration of flavor and even possible contamination due to metal release. This chemical reaction can damage the inner lining of the thermos and considerably reduce its lifespan.

Advice: Bring juices in food-safe glass or plastic containers and consume them early.

3. Soups or foods with solid pieces

While a thermos may seem ideal for keeping a soup warm, especially in winter, the reality is that many thermoses are not designed for foods with solid chunks. Thick soups, with pasta, rice or vegetables, can obstruct the closing mechanism, make cleaning difficult and generate a build-up of residue. In addition, very hot and hermetically sealed foods can generate internal pressure.

Advice: If you need to transport soup, use a thermos specially designed for food, which has a wide mouth and a safety valve closure.

How to take care of your thermos correctly

To extend the life of your thermos and ensure that it always retains the flavor and temperature of your drinks well, follow these tips:

• Clean it after each use, especially if you used liquids with sugar, milk, or food scraps. Use hot water with a few drops of vinegar or baking soda to disinfect it without damaging the materials.
• Dry it well before storing. Leave it open for a few hours to avoid bad odors and mold formation inside.
• Do not put it in the dishwasher unless the manufacturer tells you to. Excessive heat can damage insulation.
• Avoid bumps and falls, as they can affect the internal vacuum and cause it to lose its thermal capacity.

The thermos is an excellent daily companion, but it requires certain care and precautions. Avoid storing milk, acidic juices or soups with solids if you don’t want to ruin it or put your health at risk. Choose well what to wear in it, and always clean it carefully. Thus, your thermos will accompany you on hundreds of cold mornings and hot days, without unpleasant surprises.