Do You Need To Preheat A Thermos?

Thermoses allow the busiest people to enjoy a nice hot lunch or beverage, whether on the road, on the way to the office, or a long hike. It only makes sense that you want your contents to stay at a consumable temperature for as long as possible and get the most out of your thermos. Do you need to preheat a thermos?

It is advised to preheat a thermos correctly before filling it with the desired contents. Although the preheating step is often skipped, it could be easy and worth it, especially on those winter mornings when you need to pack some leftover food or a fresh and hot cup of coffee for the road.

Preheating a thermos is not tricky and won’t take up much of your time either. Continue reading as we go over why you should preheat a thermos, how to do it correctly, and why you should consider making preheating your thermos a part of your routine!

Why Should You Preheat Your Thermos?

If you notice that your freshly brewed hot cup of coffee or your hot food doesn’t stay hot for an acceptable amount of time in your thermos, don’t go into a panic just yet!

Fortunately, you don’t have to buy yourself a new thermos if you find yourself in this situation. the trick is to preheat your thermos, which is a well-known preparation activity amongst survivalists, camping enthusiasts, and even backpackers!

These people will frequently rely on their thermos containers on their journeys for storing their hot food and beverages while on the go.

Thermos-type beverage and food containers will keep your food and liquids at a warm and constant temperature by surrounding them with air, which is an excellent insulator.

If you preheat your thermos with hot liquid, such as boiling water from a kettle, it won’t only make the contents in your thermos warmer, it will also preheat the air inside your thermos.

This will ultimately cause the contents in your thermos to remain much warmer for much longer!

How Long Can Contents Be In A Thermos While Remaining Safe?

Considering how long your contents will remain safe for consumption is a factor that should not be overlooked when you have preheated your thermos and poured your beverages or packed your food in it for the day.

Given that you cooked or prepared the contents to a safe temperature and then warmed it up to a piping hot temperature, your food or drink inside your thermos will not likely go bad before you consume it.

However, it would be best to check and carefully read the instructions with your thermos to find out how many hours it can keep food and drinks safe to consume. Your food or drink will only remain safe to consume for this period if you have packed it steaming hot. The acceptable temperature would be 74°C or 165°F.

Otherwise, harmful bacteria could grow inside your thermos, contaminating your food or drink and making it unsafe for your consumption.

If you’re still unsure, you can keep in mind that once you have opened your thermos, any food or drink that remains unconsumed should be thrown out immediately.

If you find that your thermos has not kept your food or drink hot even after preheating it, it would be best not to consume it.

It is likely that harmful bacteria have already started growing, and it is not safe to consume, even if you re-heat it correctly. It would be best to throw the contents out and consider purchasing a new thermos.

How To Preheat A Thermos Correctly

Knowing how to preheat your thermos correctly will make all the difference.

To get the most value for money out of your thermos, you should always practice these steps when preheating, as it will keep your food and drink hot for longer and ensure it stays safe for consumption.

Follow these steps if you’re making use of a microwave to heat the food to pack into your thermos:

Start With A Clean Thermos

Before using your thermos, practice everyday food safety and ensure no leftover liquids or food are inside. Turn your kettle on and wait for the water to boil.

Add The Boiling Water To The Thermos

Preheat your thermos by pouring some freshly boiled water into it. How much water you pour in depends on how hot you want the contents in your thermos or how quickly you want it to heat up.

If you have the time, you can pour only a few inches of boiling water in, secure the cap of your thermos, and allow it to stand.

The steam inside the thermos caused by the boiling water will heat the rest of the thermos within a few minutes. It is recommended to allow the steam to warm your thermos for roughly five minutes.

If you need your thermos preheated as soon as possible, you can fill the whole thermos will the boiling water, and your thermos will become warm in only a minute or two.

Remove The Boiling Water From The Thermos

If you think your thermos is hot enough, you can remove the lid and dispose of the boiling water in a sink or outside.

Keep in mind that young children should be helped when opening a thermos containing hot water, as they could burn themselves.

If you want to be very accurate regarding the temperature of your preheated thermos, you can use a thermometer.

To keep your food hot for as long as possible, it is advised to do this step just before leaving your house.

Fill Your Thermos With The Contents Of Choice

After you have emptied all the hot water, you can pour your drink or place your food inside your thermos and enjoy it later on while it is still at its hot and comfortable temperature!


Knowing the benefits of preheating a thermos, you will only benefit from making it a part of your morning routine for any food or drink you want to keep warm.

However, it is crucial to keep in mind that your food has to be stored safely and at the correct temperatures for it to remain safe for consumption. Preheating a thermos is well known, and you will not regret it!


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