How to Clean a Flask in 6 Simple Steps
Whether you use it for lunchtime soups, a warming cup of tea on a long journey or a reviving coffee when out on a hike, a stainless-steel flask is a versatile piece of kitchen kit. And, with the drive to reduce waste, a reusable and durable flask is also good for the environment. But, as all flask users will know, this handy thermal container does have a habit of getting a bit grimy and stained. Then there’s the likelihood that at one time or the other, you’ve left it in the car, only to discover it a week or so later, still filled with leftover soup that has gone pretty yucky.
One of the main downsides of the thermal flask is that is can be a bit tricky to clean and will more often than not need a lot more than a quick rinse. We take a look at how to clean a stainless-steel flask in six quick and easy steps.
A Thorough Initial Rinse
As with most things in life, prevention is better than cure so aim to get into good habits from the start when buying a new thermal flask. As soon as you finish with your flask, empty away any residue liquid and rinse immediately with hot water and a squirt of dish cleaner. If you have a bottle brush, give the inside of the flask a good scrub, then rinse again before placing the flask upside down to drain. It’s important to always ensure your flask is totally dry as this is a must-do when it comes to how to clean a flask.
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Soak With Boiling Water
To remove very light staining and food or liquid residue that a quick rinse doesn’t quite shift, then all you need to do is turn up the heat. Boil a kettle of water and then carefully fill your thermal flask to the brim, with a drop of dish detergent if you wish. Now leave the filled flask to one side for five to 10 minutes to let all that heat do its work. Give the insides a quick scrub with a bottle brush, paying attention to the lid and screw top section before rinsing.
Get Fizzy With The Baking Soda
Ok, we have all done it; totally forgotten to clean our flask, only to discover it still has some food or drink remains inside a few days later. By now, what was left inside the flask will have dried, crusted and has started to smell and so a quick rinse simply won’t cut it. It’s time to break out a baking soda mix and get a bit tougher on these stains.
Pour half a cup of distilled white vinegar into the flask, then add one tablespoon of baking soda for each cup the flask holds. The vinegar/baking soda mix should froth up nicely and will wear down the stains as well as kill any bacterial nasties. Once the fizzing starts to subside, fill up the rest of the flask with hot water and let it sit for around 10 minutes, with the lid off. As it rests, the water and baking soda solution will soften and remove any stains that remain. Then empty the flask and rinse with hot water again and leave to thoroughly dry.
Shift Stubborn Odors
As well as grime, your flask can also hold on to odors if you are not on the ball when it comes to cleaning after every use. Putting the lid back on to the flask when storing or when the insides are still damp is also going to lead the flask to become a bit whiffy. If you find your flask has a musty smell when you come to use it, then turn to your kitchen cupboard. White vinegar or lemon juice are both good at whipping those whiffs into shape. Simply fill the flask to three-quarters full of very hot water then top up with either vinegar or lemon and leave to soak. Make sure you then rinse the flask well and the insides should smell sweet again. And you find your flask has a metallic smell that is affecting the taste of your drink, here’s a great tip – pour in very strong black tea and leave for a couple of hours. Trust us, it works!
Shifting Really Stubborn Stains
Despite all your best cleaning efforts, the insides of your stainless-steel flask can get stained over time, with hard water and coffee two of the main culprits. If scrubbing and soaking is not working, then we have two home remedies that will get tough on those stubborn stains:
- Denture tablets: Designed to remove stubborn stains on dentures, denture tablets are an effective way to shift those marks and with their antibacterial properties, are also perfectly safe. All you need to do is fill the flask with water and drop in a couple of denture tabs. The hotter the water, the faster the fizz and so the cleaning action. Leave for a few minutes without the lid on, then when the fizz subsides, give a good scrub with a bottle brush and rinse thoroughly several times.
- Ice and salt: Fill your empty flask with crushed ice until it is about a quarter full then sprinkle two to three spoonfuls of salt over the ice. Coarse or sea salt is best as they have larger grains and get to work faster. Now pop on the flask lid and give it all a good old shake for a few minutes and the ice/salt combo will act as an exfoliator on those stubborn inner stains. When you’re done, empty out the ice and salt and then thoroughly rinse with warm water and leave your flask to dry.
Clean Up Outside
Don’t forget the outside of your flask to remove water stains and keep it in tip-top condition. Here’s how to clean a flask with leather once it has been thoroughly rinsed and has been left to dry. Dab on a little lemon oil – baby oil will also work – with a dry cloth and work into and across the metal. Now take your leather buffing cloth and polish the surface to remove not just the oil but surface stains too, leaving your stainless-steel flask with a lovely shine.
What Not To Do
Now you know how to clean the thermos bottle, here are a few tips on what not to do.
To protect your flask and preserve its shelf life, never use chlorine bleach or a cleaner that contains bleach as your flask has a liner which will be corroded by the chlorine. Also avoid using any abrasive cloths or cleaners as these will scratch the flask’s outer surface. When storing your newly cleaned thermal flask, always ensure it is thoroughly dry inside and don’t pack it away with the lid screwed back on but leave it open and the lid to one side. This way, you will prevent any musty smells developing inside and your flask will be fresh, clean and ready to go next time.