Thermos, skis, boiling water: a thermos choice

Thermos is a very winter article: as a rule, neither an “ice age” at the local ice rink, nor a ski trip in the park, nor a banya with birch brooms can do without it… Obviously, it has uses in other seasons as well: we go fishing with it in summer, or pick mushrooms in fall, but maximum pleasure and benefit can be got from it only in winter.

Consultant: Ekaterina Grzhibovskaya, Commercial Director of Cold Technology 2000 Ltd.

How a vacuum flask became a thermos

We owe the birth of the thermos to basic science: scientists-physicists did a lot for it – probably because they liked to indulge in hot tea even in the field.

At the end of the century before last the German Adolf Ferdinand Weinhold invented the double-walled glass container, with air pumped out between it. Eleven years later, in 1892, the Scotsman James Dewar, whose aim was to reduce heat loss in such a device, turned a glass box into a narrow-necked flask. He applied a reflective layer of silver on the inner surfaces of the vessel and “dressed” the flask in a metal casing.

As a physicist, Dewar made great scientific advances: he was able to keep liquid and solid hydrogen in his vessel. Scientifically, it was a brilliant invention, but only an equally brilliant businessman could grasp the practical benefits it would bring to mankind. Reinhold Berger, a Berlin industrialist, was such a visionary.

He understood that if we make the vessel compact enough and “teach” it to close hermetically, then it can easily be taken with you, but not with a “scientific” filler, but with hot tea, for example.

Since it is inconvenient, dangerous and indecent to drink hot drinks from the neck, the ingenious thing is simple – he complemented his device with a cup- lid.

So, at the beginning of the twentieth century, an enterprising German founded the company for the production of “vacuum flasks” – as they were then called.

You may ask what the Greek has to do with it? Just the word “thermos” of Greek origin from therme – “hot” , and since 1904 the familiar to us subject began to be called just that.

From the same year a well-known German company has been producing the products under the THERMOS brand, but the modern market is literally flooded with thermoses produced by little-known companies, and it is rather difficult to choose a quality device among this variety.

Keep it cool! It is hot and cold?

Contrary to its “hot” name, not all thermoses can keep hot tea, but all perfectly keep cold. The number of hours of heat preservation, declared by the manufacturer, you can safely multiply by 2.5 or 3 – get the number of hours of preservation of cold.

By the way, it is not so easy, in terms of science, to define what is “warm” or “cold”. For example, in America there is such a standard: if the product or a drink is hotter than 50 degrees, then it is considered hot.

Each company-manufacturer of thermoses has its own idea of “hot” temperature, and when buying a particular product, it is not bad to ask about the figures. For example, by “keeping warm” THERMOS means keeping the temperature not lower than 70 degrees C, which is the minimum temperature at which you can brew tea or coffee in hiking conditions.

Versatile and non-sinking thermoses

Modern thermoses are not only camping tablecloths. In addition to their direct duties of keeping food warm, many of them have added all kinds of talents and skills. Judge for yourself – thermoses became universal and even non-sinking: they can swim even completely filled, to entertain children and many other things!

Thermos bottles are developed mainly for people who lead an active life and are keen on sports: they allow to drink a beverage at the right temperature without opening a thermos and without pouring the drink directly while walking, running or cycling.

Devices for drinking can be of 2 kinds: in the first one it is enough to press the special valve – and you can drink through a tube, in the second – the liquid enters through slits in the cork. Most bottles do not retain heat and are designed for cold beverages.

Important design features for “bottles” include a neck that is wide enough for you to put ice cubes in your drink, and a shape that provides a comfortable grip.

Thermoses with coffee-presses help to properly prepare and keep hot the ground coffee or herbal tea. Piston-press technology is very popular now for preparation of these drinks, and glass French-presses are convenient for all but one thing – coffee in them quickly cools down.

Floating thermos – a miracle, indispensable in camping, especially in “kayak raids. Even if it is filled to the top, it will not sink if exposed to water. Such thermos is a record holder on heat retention, holds up to 12 hours.

Children’s thermoses are the devices made in a child funny and funny design. Joyful colors and favorite animals will help to feed your baby under any circumstances – after the training, visiting the doctor, a hike or a walk.

For a child of secondary school age this thermos can be given to take to school or to the training – as a rule, the size and weight of children’s thermos allow it. It is very important to remember that the temperature of the drink must be suitable for drinking even when poured into the child thermos, because the child can get burned.

That is why children’s thermoses of world famous brands indicate the preservation of cold drinks and juices and drinks up to 50 degrees, as children do not need boiling water and drink, as a rule, directly from the thermos ready drinks.

Children’s thermoses must meet the highest standards of quality, material, safety, reliability and well thought-out details for easy, convenient and safe use. By the way, equipping the children’s thermoses drinking tube is not a fun, but the concern for safe use – especially on the road.

Three meals for one thermos

Are there thermoses intended only for drinks – with a narrow neck, there are – only for food – with a wide neck, and there are universal. The latter is the best option for those who have a large family and the thermos will be used for different needs and situations.

As a rule, these are big enough vessels with wide necks so that it was convenient not only to pour drinks there but also to put and take out the second courses. If the thermos is purchased just for them, then you need a food thermos – it has a larger diameter and a wide neck.

If you want to take a “complex dinner” with you – both the first and the second at once, then you have to use a thermos with food containers, which are put in it one on top of the other. You can put different dishes in them.

Minus of this approach is lower ability to keep warm though on the market there are some models for example Thermos JLN 1400 for individual lunch that keep warm for 24 hours.

Standard features of conventional stainless steel thermoses are 8-10 hours. Ideally, each container-bag should be equipped with an individual tightly closing lid, which will give the possibility to use them without a thermos: put them in the fridge, heat food in them in the microwave.

There are “kids” in the family of food thermoses – these are thermocaps. They won’t feed a company, but thanks to their lightness and small volume up to 0.5l they are ideal for individual use. , are very suitable.

Vacuum thermoses: the heat of the double bottom

Bright colors and funny pictures – obviously not what you should look for when choosing a thermos. Specialists advise to pay attention to the material of the body.

The absolute leader in durability, practicality and – what is important! – In terms of style it is stainless steel, but in terms of hygiene the winner is glass.

For a long time steel and glass thermoses were compared by weight of flasks, and the thermoses with glass flasks won in this comparison. Modern production technologies have improved steel products so much that they have become lighter and more compact than their glass “brothers”. And what else do you need to look for in “material science”??

The first important point – the thermal conductivity of the material itself. For the average consumer it is important that the food or drinks are kept hot for a long time, and from this point of view glass is preferable. The fact that the food-grade stainless steel, of which, as a rule, are made metal flasks, heats up long enough, while taking some of the heat of the product.

A glass flask heats up very quickly and all the heat stays in the product. If you chose a thermos with a metal flask then before you pour your drink into it scald it with boiling water to make it hotter and the drink will stay hotter for longer.

However, with the high-tech manufacturing of vacuum stainless steel thermoses the temperature retention rates are far beyond the usual standards 8-10 hours . Such thermoses can be used in extreme conditions -20-50 degrees for a long time 24-48 hours .

Thermos must last a long time

The second benchmark is the durability of the material. Here, of course, steel wins, because glass is more fragile. Quality thermoses with metal flasks are not afraid of dents, bumps and even drops on hard surfaces, because their body is not damaged.

Some models made of the so called “spring steel” can restore its shape after a collision. However, if the metal flask still forms a dent, then the integrity of the vessel will be compromised, and the ability to retain heat is lost completely.

Many firms that produce thermoses with glass flasks, produce replacement flasks, but in today’s rhythm of life it is unlikely that someone will look for a suitable flask – it is easier to buy a new thermos.

It is considered that the glass flask can not stand a sharp temperature drop, so you can not pour boiling water into it if you have recently brought it from the cold – for example, from a walk or just from the balcony. To date, most of the world’s famous manufacturers have eliminated this drawback.

But the most important thing when choosing a material is its inertness, that is, its neutrality towards the foodstuffs in contact with them. The material must be of very high quality – not loose, easily washable, does not allow any chemical reactions with the products.

If the material of the flask is steel, it must be a chrome-nickel alloy with a grade no lower than 18/8 – the so-called food grade stainless steel. The easiest consequences of using a thermos flask of low-quality steel are coffee-flavored tea or fish-flavored chicken broth and non-washable walls.

After several uses of this flask you will want to eat or drink from it only as a last resort. But more serious consequences can also be: this and allergic reactions, and poisoning, and with systematic use – the accumulation of harmful substances in the body.

I want a thermos! Who’s responsible for the heat?

The manufacturers single out two main factors that affect heat retention in a thermos:

– The quality of the deep vacuum that is created in the thermos – between the walls to keep the temperature,

– the brand of stainless steel that the thermos flask is made of, which will retain that vacuum.

Unfortunately, it is possible to check how adequate the deep vacuum technology is and how good the stainless steel is only after purchase – already in the process of use. Poor-quality vacuum and wall material can make itself felt at the first use, and during the year – the heat will be preserved worse.

To protect yourself from buying a substandard product, we advise you to choose the products known brands with a manufacturer’s warranty of at least 5 years. This indirectly confirms the high quality of the thermos. High-tech products are given a branded warranty of 5 to 15 years. Needless to say that if in the technical specifications of the thermos you can not find any data on the vacuum and steel, it is better to postpone the purchase!

How to choose a thermos: our advice in big letters

Clever details, small construction peculiarities may not draw your attention when you buy it, but they significantly add to the comfort of using the thermos. The obvious pluses include:

– Non-slip, wide base,

– guiding for pouring in a neck or in a cork if the liquid is poured through the cork ,

– An additional mechanism for closing and locking the lid for example, if the lid is not screwed, but hinged, it can be a lock in the form of a ring or button ,

– air inlet valve on the inside lid for easier opening without the “sucking” effect of the lid,

– demountable cork design for washing the thermos,

– Folding handle that allows you to conveniently place the thermos in a bag or backpack,

– snap hook to secure the thermos to your backpack,

– dishwasher safe,

– possibility of installation in a car holder for mugs as a rule, thermoses of up to 0.5 l volume correspond to this size ,

– the coating of the stainless steel body with a special lacquer that prevents stains and protects against scratches.