While thermoses offer convenience for storing beverages, health experts advise against keeping milk or tea in them to avoid potential health risks.

According to Sohu, not all beverages are suitable for being stored in insulated flasks, as such storage can not only spoil the drink but also pose health hazards. Below are five types of drinks to avoid keeping in these containers:

Milk

Many people like to heat milk and keep it in a thermos for later consumption on cold days. However, this is not the recommended approach.

Milk is highly nutritious, and the warm, enclosed environment in a thermos encourages bacterial growth, which can cause the milk to spoil quickly. Additionally, the proteins in milk can change when exposed to high temperatures for extended periods, diminishing its nutritional benefits.

If you need to store milk in a thermos, it is best to consume it within an hour.

Herbal medicine

Storing herbal medicine in a thermos for convenience is a common practice. However, herbal mixtures can be complex, containing both acidic and alkaline components.

Thermoses are usually made from stainless steel, which contains metals like manganese, iron, chromium, and nickel. When herbal medicine interacts with these metals, chemical reactions may occur, potentially reducing the medicine’s effectiveness or generating harmful substances.

Furthermore, herbal medicine can deteriorate if kept in high temperatures for too long. For better preservation, store herbal medicine in a glass or ceramic container.

Acidic or carbonated beverages

Beverages such as fruit juices and carbonated water are also unsuitable for thermos storage. The acids in these drinks can corrode the thermos’s stainless steel lining, damaging the protective coating and potentially releasing heavy metals into the liquid, posing a health risk.

Additionally, if carbonated beverages are stored in a thermos and the container is shaken, the buildup of carbon dioxide can create high pressure, leading to the risk of explosions or spills when opening the lid.

It is safer to use glass or ceramic cups for storing these types of drinks.

Salty drinks

Beverages containing salt should not be left in a thermos for extended periods. Even with corrosion-resistant coatings, the protective layer of thermoses can still be damaged by saltwater, potentially releasing heavy metals that may be harmful to health.

Tea

Tea contains tannins, caffeine, essential oils, and vitamins, which are best extracted with water heated to around 80 degrees Celsius. Prolonged high temperatures inside an insulated flask can also destroy the vitamins in tea, evaporate essential oils, and over-extract tannins and caffeine, leading to a bitter taste and a higher risk of harmful compounds.

Moreover, tea that sits too long in a thermos can leave behind residues that are difficult to clean, making the thermos appear dirty.