If you’ve ever wondered, “How long can you keep food hot in a flask?” you’re not alone. Insulated flasks are specially designed to keep hot and cold foods at the right temperature for a longer time. With the right thermos, you can avoid allowing your food to enter the “danger zone” when you’re at work, travelling, or on a long commute.
The question is, how long can you expect your flask or thermostat to keep your hot lunch at the right temperature? Perhaps even more importantly, can you still eat food from a flask after it’s no longer as hot as it once was?
Let’s take a look at the basics of keeping your food hot and preserving food safety when using a flask.
How Long Does a Food Flask Keep Food Warm?
Not all food containers are built with the same quality of materials. Lower quality materials may mean you can only keep your food warm for two hours or so. Additionally, the kind of food you’re transporting and the food preparation (like whether you use boiled water or roasting methods) will also have an impact on how long your food remains safe to eat.
When you’re trying to keep your food hot or cold in a carefully-constructed flask, it’s worth following the instructions and information provided by the flask manufacturer. Some flasks will require you to take certain steps to ensure your food doesn’t spoil faster than it should.
Will Hot Food Spoil in a Thermos?
Hot food shouldn’t spoil very quickly in a thermos. However, your food will not remain safe to eat forever.
Ultimately, you’ll only be able to safely eat hot food from a thermos or flask if it doesn’t drop below the temperature of 40 degrees Fahrenheit or 60 degrees Celsius. Underneath this temperature, a hot food container is sitting in the “danger zone,” which means bacteria can grow in it.
Though food in a thermos won’t necessarily spoil straight away after its heat starts to drop, you should be extra careful about which foods you eat out of a thermos or flask. A drink or liquid-like coffee will generally be fine to drink when it’s just warm. On the other hand, leaving milk to sit for several hours in a thermos is extremely dangerous.
As a general rule, try to avoid allowing your food to enter the danger zone for food temperatures, and follow the instructions given by your flask manufacturer. Don’t pack beverages and foods you know will spoil quickly.
How Long Can You Keep Soup in a Flask?
As mentioned above, there are various rules to follow to determine how long you can safely keep food warm in a thermos or flask. For instance, if you store a lot of food in a thermos, the bigger the thermos, the more difficult it will be for the food to stay warm.
If you have a thermos with a wide mouth and keep opening it to expose the contents to air, this will increase your chances of the food going off.
Soup is one of the most common foods to keep in a thermos or hot flask. You can easily keep soup in a thermos for a few hours at a time without worrying about it losing its heat. Sometimes, a thermos can keep piping hot soup warm for up to 7 hours. However, you’ll need to make sure the soup is hot, not just warm, before placing it in the flask.
Getting your lunch to the right heat before you place certain foods in a thermos can help it last longer. Certain foods simply won’t be well suited to a flask or thermos at all. While you can keep soup warm when packing school lunches or food for work, you should avoid keeping milk or chicken in a thermos. It’s also best to avoid placing rice in a thermos.
How Do You Keep Food Warm in a Flask?
Learning how to keep food hot in your flask is a good idea if you’re going to be eating warm leftovers at work or taking a liquid like coffee or soup with you in a thermos on the go.
First, make sure you know which foods shouldn’t be kept in a thermos, like milk and rice. Next, consider the materials of your thermos or flask. A product like stainless steel will often be better at keeping food hot or cold than plastic.
Other points to keep in mind when trying to keep your food at the right temperature in a thermos include the following.
Prep the Night Before
If you plan to take leftovers with you on the move, preparing your food the day before is a good idea. Straight after cooking your lunch, place the food you want to eat in the fridge for the night to keep it at an ice-cold temperature. You will then be able to reheat your food the next day for your lunch.
Make Your Food Extra Hot
If you want to keep heat in your thermos for as long as possible, getting your food to the right heat before storing it is a good idea. Your soup and other foods should be as hot as possible before you fill your thermos. Heating your food to the highest possible temperature range will ensure it can stay hot in a thermos for longer. Plus, piping hot food will kill off any harmful bacteria.
Preheat your Thermos
Preheating your thermos can be a good way to ensure your foods stay hot. If you’re going to pack foods you want to eat hot within a couple of hours, consider filling your thermos with boiling temperature water for a few minutes before packing hot food into it.
Boiling water will warm the inside of the thermos while killing off any bacteria. Remember, you need boiling water to prepare hot foods in your thermos. If you’re packing cold food, boiling water is also great for cleaning a thermos first.
Remember to use the right size of container to stop food spoiling too. If you want to avoid your thermos making your food unsafe, don’t put smaller kid-sized portions into a large thermos. This makes it easier for the heat to dissipate over time as the food moves around in the thermos.
How Do You Know if Food is Safe from a Thermos Flask?
Concerns about food spoiling can make it difficult to enjoy the hot food or cold food from your thermos. The good news is that thermos flasks and similar products are designed to keep cold food cold and hot foods at the right heat for as long as possible. As long as you heat food correctly before you store it in your thermos, your food should stay hot for several hours.
Whether packing food for school lunches or your own workplace meals, the best thing you can do is prepare. If you have a stainless steel thermos, use hot water (boiling water) to heat the inside of the thermos before you fill it. When you boil water for the inside of your thermos, this also gets rid of extra bacteria.
It’s also worth having a thermometer handy, so you can check the temperature of your food whether you want to keep it hot or cold. Being able to test the temperature of your lunch will help to ensure it hasn’t entered the danger zone.
Finally, make sure you conduct a smell test before drinking your soup or eating your hot or cold lunch, as this will help you determine whether something doesn’t smell right before eating.
Enjoy Your Hot Meal
So, answering the question, “how long can you keep food hot in a flask” can be complex because different flasks deliver different performance levels. Sometimes, you’ll be able to keep a hot lunch popping hot for as long as five hours. However, how long you can keep food hot in a thermos will differ from how long you can preserve hot food in a standard vacuum flask.
Follow our simple tips and enjoy your hot meal safely from your thermos!
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Tom is a former chef turned full-time food blogger. He has always been passionate about food, and loves nothing more than experimenting in the kitchen and sharing his recipes with others. Tom’s blog is one of the most popular food blogs on the internet, and he has won numerous awards for his cooking. When he’s not blogging or cooking, Tom enjoys spending time with his wife and two young children.