How to Safely Clean a Thermos and Use It Effectively

Properly cleaning your thermos will allow you to use it for years to come.

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There's nothing worse than opening up your to-go coffee cup, ready to enjoy a delicious (and healthy) sip, only to find your beverage at room temperature. A thermos allows for hot or cold retention, keeping the contents inside as close to the original temperature as possible. They're also meant for taking on the go and can stay secure whether you're just heading to the office with cold water or going on a camping excursion with healthy soup.

Maintaining your thermos is a bit different than you may be used to with your typical reusable bottle or container. While many thermoses claim to be dishwasher-safe if placed on the top rack, when in doubt, hand-washing is the way to go so the insulation does not get damaged. But don't worry, there are a few simple tips and tricks you can follow to keep your thermos in top shape for years to come. Read on for everything you need to know about how to clean a thermos.

How a Thermos Works

A thermos uses vacuum-insulated technology to keep hot contents hot and cold contents cold. The bottle-within-a-bottle design has a vacuum between the two walls, which allows whatever you put inside to stay at the same temperature longer.

The design doesn't conduct heat, and also prevents condensation from forming outside. It stays room temperature/cool to the touch, even when something inside is icy cold or piping hot. Thermoses are widely available from different brands, in varying capacities and colors.

How to Clean a Thermos

Here are three popular methods to get your thermos clean of coffee and soup stains, and even to remove lingering odors.

Vinegar and Baking Soda

The combination of vinegar and baking soda is a tried-and-true cleaning hack for common kitchen problems.

  • Pour 1/2 cup distilled white vinegar into your thermos and sprinkle 1 tablespoon of baking soda on top. The combination will undergo a chemical reaction to cause frothing.
  • Add in some warm water and allow the mixture to sit for about 10 minutes.
  • Use a bottle brush or cleaning cloth with hot water to give the inside of your thermos a good cleaning. Repeat if needed.

Denture-Cleaning Tablets

You might be familiar with the cleaning power of denture tablets if you wear a retainer or dentures. They're also an effective way to clean your thermos!

  • Fill 1/2 to 3/4 of your thermos with warm water.
  • Drop a tablet into the thermos and allow it to sit until it has stopped fizzing, 5 to 10 minutes.
  • Use a bottle brush or cleaning cloth with hot water to give the inside of your thermos a solid final cleaning. Repeat if needed.

Ice and Salt

  • Add crushed ice to your thermos with about 2 tablespoons of sea salt. (Salt naturally has antibacterial properties.)
  • Secure the lid and shake well, as with a cocktail shaker.
  • Use a bottle brush or cleaning cloth with hot water to give the inside of your thermos a good final cleaning. Repeat if needed.

As we mentioned, many thermos manufacturers suggest hand-washing your thermos, even if it is labeled as a dishwasher-safe product. You risk damaging the vacuum seal which allows for insulation by placing it in the dishwasher, defeating the purpose of having a thermos.

How Not to Clean a Thermos

Now that we've covered a few tips for cleaning your thermos, there are also a few things you should NOT do while cleaning it.

  • Do not use chlorine or bleach to clean your thermos. These chemicals can be too harsh and may damage the stainless-steel interior.
  • Do not use super-hot or boiling water to clean your thermos. Not only will using boiling water potentially damage the paint or exterior of your thermos, it could also cause melting and even break the vacuum seal, which will prevent your thermos from properly insulating.

Tips to Maximize the Staying Power of Your Thermos

Thermoses are designed to be used with liquids, so this isn't the place to shove any old leftovers. Think soups and stews, coffee and tea, or even milk and juice. Here's our best tip to maximize the insulating abilities of your thermos for cold and hot contents, respectively.

For Cold Contents

  • Stick your thermos in the fridge or freezer in advance. In a time crunch? Fill it with ice and water for a few minutes.
  • Take your thermos out of the fridge and dump out the ice water.
  • Add in your cold coffee, juice or smoothie and secure the lid.

For Hot Contents

  • Fill your clean thermos with hot water and put the lid on.
  • After a few minutes, remove the lid and empty out the water.
  • Add in your hot soup, tea or coffee and secure the lid. The temperature of the contents should be hotter than it would be if you were to consume it immediately, so use caution when filling your thermos.

Don't forget, once you've opened your thermos to enjoy your contents, anything not enjoyed should be tossed to prevent harmful bacteria from growing.

When to Throw Out a Thermos

Even with proper care and cleaning, not every item in your kitchen will last forever, including a thermos. If you find that it's not keeping the contents insulated any longer, whether hot or cold, it's probably time to say goodbye. Also, look out for any chips or cracks on the interior of your thermos—use that flashlight on your phone if you have to. If the inside of your thermos is damaged in any way, it's time to replace the thermos.

Bottom Line

Thermoses are a useful tool to have on hand year-round. To make sure they remain clean as whistles, use one of the recommended cleaning methods: vinegar and baking soda, denture tabs, or ice and salt.

Heading out on a camping adventure? Not without some tasty recipes that will keep you feeling full! Take a look at these 24 Healthy Camping Recipes.

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