There’s a reason why thermoses come with a lifetime guarantee from top manufacturers. No matter how long you’ve had one, there is always some dirt, dust, or debris that collects in its interior. Getting rid of this buildup is essential to keep the thermos safe and clean for drinking water. You can use different chemicals, including vinegar, lemon extracts and dish soaps, to clean them.

Methods to Clean the Interior of a Thermos

1. Baking soda and vinegar
2. Denture cleaning tablets
3. Dishwasher powder
4. Eggshells
5. Lemon juice
6. Ice and salt

1. Baking Soda and Vinegar

Baking soda is already in your kitchen cupboard, so all you need to do is grab a bowl and add 2 cups of water to it. Then add one tablespoon of vinegar. Stir the mixture thoroughly to incorporate the solution with the baking soda before using it on your thermos. The solution should be clear, almost transparent, but not too runny. You should mix the solution well into the thermos. After the process, you can wash it inside and out by pouring hot water over it.

2. Denture Cleaning Tablets

These tablets are easy to find and help in removing stains from the inside of your thermos. You will need to dissolve one tablet of denture cleaning tablets in 1/4 cup warm water. When the tablet has dissolved, mix your solution and pour it into your thermos. Once you have poured the solution, fill it with boiling water and let the thermos sit for a few minutes before draining it.

3. Dishwasher Powder

This is one of the most accessible ways to clean your thermos, and it’s also easy. Just fill your thermos with warm water and add a teaspoon of dishwashing powder. Once you have added the powder to the water, fill the thermos with excess warm water and shake vigorously for a few seconds. Then empty all the water from your thermos and rinse it thoroughly before filling it again. 

4. Eggshells

If you don’t have any baking soda, vinegar, or dishwashing powder in your pantry, you can use eggshells to clean your thermos. The easiest way is to grate an eggshell into tiny pieces and dissolve it in water. Let the eggshell dissolve for a few minutes before adding more hot water. Shake vigorously for around 10 seconds and then rinse it thoroughly.

5. Lemon Juice

Lemon juice is one of the easiest ways to remove stains from your thermos. Just add some lemon juice and fill it with boiling water. Let it sit for 5 minutes before pouring it out. The lemon juice should dissolve any stains or rust on the thermos, leaving it clean and fresh.

6. Ice and Salt

If you have a stainless steel thermos with stubborn stains inside, you can try cleaning it with ice and salt. First, put some ice cubes in your thermos and then add plenty of salt onto them. Swirl this mixture around for a few minutes until the ice has melted. Then pour out the water until there are no more visible particles in it. Repeat this process until all of the stains are removed from your thermos before rinsing it.

Can Bleach Ruin a Thermos? 

Although some thermos manufacturers recommend against using bleach to clean a thermos, many people still choose to use it. Bleach is considered more potent than other cleaning solutions and can easily remove stubborn stains inside a thermos. However, it can fade the color of a thermos or damage the plastic parts, which means you will have to replace your thermos before its useful life ends. 

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Having a well-maintained thermos can help you to stay properly hydrated. Cleaning it regularly ensures that you have a usable drinking vessel at all times. You can purchase chemicals from home improvement or department stores to clean the interior of your thermos. It is also essential to thoroughly clean the outside of a thermos because mold and mildew can easily grow on its surface if it’s not kept clean.

Frequently Asked Questions

Q. Why do thermos lids get moldy?

A. Thermos lids are made of plastic which can be damaged by hot water and many cleaning products. The cover of your thermos is also the part exposed to the outside, meaning it has more chance of becoming dirty or collecting bacteria. Keep the lid separate from the rest of your thermos when cleaning it with hot water. You can use a soft bottle brush to clean it gently if possible.

Q. Why do I get rust stains in my thermos?

A. Rust stains are caused by water with traces of iron in it. Although this happens to all thermos over time, soft drinks are more likely to cause rust because they are acidic. If you notice any rust build-up on your thermos, try to rinse it with white vinegar to remove the stain before rinsing the thermos again with warm water.