FAQ

Furthermore, Rotho products also do not include materials containing cadmium. The general rule for all plastic products is that they must not contain more than 100ppm lead or 1ppm cadmium. In the case of plastics that will come into contact with foodstuffs, these thresholds are significantly lower. In the past, cadmium compounds were used for plastic colouration.

All plastics have a glass transition range. In other words, there is a range in which their properties change from stiff and inflexible, like glass, to partially elastic and flexible. In the case of our plastics, this range is around -10°C. This range can be made even lower by the use of certain additives, and we do this with our freezer boxes. The plastic used for these has been specially developed for the purpose, meaning that even at around -18°C, the material retains its residual flexibility. It therefore does not split, as glass does, when you handle it.

Fun fact:

Are frozen goods heavier? If a kilo of feathers, a kilo of water or a kilo of iron are frozen, they do not become heavier. They still weigh 1 kg. What changes is the space they take up. With water, we know that the density changes from 1 kg per litre to about 0.9 kg per litre – otherwise, ice would not swim on top of water. And as a result of its linear thermal expansion coefficient, iron definitely requires less space. In other words, its density increases.

Fennel, for example, contains anethole, among other things. This only occurs in notable concentrations in fennel, aniseed and star anise. This anethole is chemically related to SAN, which is the reason why it can penetrate into the SAN, disturbing the SAN’s highly transparent structure, resulting in discoloured spots. We also recommend using glass storage containers, rather than plastic containers, for the following foodstuffs: seeds, flavoured tea and cinnamon. These foods too also include substances similar to the styrene in the SAN, which leads to the material becoming cloudy and its surfaces roughening.  The majority of citrus-like or peppermint-like flavourings pose no problems for SAN.

Our products can in principle be sent to recycling, as they are made from high quality plastic. Some time ago, we began partnerships with some major companies, in order to master the main problem associated with materials recycling. The main problem with materials recycling is the logistics required in order to be able to collect the plastic waste in a manner in which less oil is used for the transport than is contained in the actual product. For a while now, we have therefore been obtaining so-called post-consumer polypropylene. On another production line, we use so-called post-industrial polypropylene for some products. This occurs as the result of processing waste from the plastics industry. So today, more than 25% of our products are made from recycled plastic, and this proportion is continuously increasing. Because Switzerland is a European leader in recycling plastic waste, recycling more than 99% of it, Rotho products that have reached the end of their life can be sorted for disposal at the operations centre.

Let’s take a short detour into the periodic table of the elements: Water – which consists of hydrogen and oxygen – is a dipole. This is a result of the wildly differing electronegativity, ie how strongly an element attracts another electron, in order to achieve a stable configuration (noble gas state/octet rule). We know that hydrogen gladly emits its electron, whereas oxygen would be pleased to absorb an electron. The result is that the water molecule’s electric charge is powerfully displaced to oxygen, forming a so-called ‘polarised bond’.  
Now let’s take a second short detour into the world of chemistry. Carbon is in the middle of the periodic table, and can therefore barely decide whether it wants to emit or absorb electrons. The result is that bonds between carbon and hydrogen are not polarised bonds.
Polypropylene consists solely of carbon and hydrogen, and Rotho’s microwave boxes are made from polypropylene.
But back to the microwave:
The microwave attacks polarised bonds and attempts to displace the charge. The molecules don’t want that, and so they move backwards and forwards in the microwave’s field. At the same time, the molecules rub against one another, generating frictional heat – just like when you rub your hands together. If I now fill a Rotho box with water, put it in the microwave and switch the microwave on, the water molecules rub against one another, at the same time heating one another. The Rotho box is not heated by the microwave. The heat you can feel on the microwave box is emitted heat, transferred from the heated water to the box. Think of it as being like a saucepan in reverse. The pan is heated on the hob, and its heat is then transferred to the water.
And it is this direct heating of the food that makes the microwave so interesting, as loss of energy during heat transfer (hob to pan, pan to food) is prevented. What’s more, the microwave also directly heats the food’s core, not from outside to inside via diffusion and convection, like a pan does.
If water in one of Rotho’s microwaveable containers is heated in the microwave, the microwaveable container cannot become damaged, no matter how long the water is heated, or even if it completely evaporates.
This use can therefore be described as being absolutely safe.
Because lots of types of food contain water (dough, starch, potatoes, cucumbers, peppers, meat and sausages, milk etc), these can be heated in the microwave. How long these products need to be heated is different for every type and combination. It is therefore only possible to provide tables for pure components. But what use is it to the consumer if he or she has to divide their spring vegetables of peas, carrots, broccoli and cauliflower into their individual components, in order to be able to calculate the time needed for the vegetables’ average temperature to reach their desired eating temperature? It is therefore much better to simply rely on the information on the frozen vegetables’ packaging, as the manufacturer knows the composition.
For more advanced users, the question of heating food that has already been cooked comes into play.  Because the combinations are infinite, it is not possible to state generally applicable times after which the combinations of food have reached a certain temperature. The recommended course of action – and, to the best of my knowledge, this is what is also stated in the microwave’s specification – is to select a short heating time, then occasionally check and heat further until the desired temperature has been reached.
But if you want to go a step further, you must try the products in our Clever range. Thanks to the use of special plastics, we have succeeded in increasing the temperature resistance of the products in this range to 180°C. So, for example, you can heat a pizza on the microwave plate to 180°C without problems. But this also means that you cannot bake the pizza at 250°C.
If we can rule out roasting at more than 180° fat temperature and baking at up to 250°C, then our steamers and egg, rice and pasta cookers can be of assistance.
First, let’s look at the egg cooker, which denaturises and solidifies your boiled egg at between 70°C and 100°C, within just a short period of time. A disadvantage is that you cannot cook your bacon with it at the same time. This can therefore not be seen on the packaging, nor in the preparation guidelines on the flyer included with the product.
Steamers, pasta cookers and rice cookers use water, and therefore do not heat to over 100°C.  
Despite your apprehensions, even the steamer is made from plastic (in this case, transparent).  
From my own experience, I can however say that the details on the flyer enclosed with the rice cooker are a little overoptimistic. The cooking time is considerably longer, especially if you are preparing larger quantities of rice. That said, the risk of scalding is low.
The symbols on the website, as well as those on the products, are not governed by any generally applicable regulations. However, Rotho is currently working with the General Plastics Industry Association on developing such a uniform regulation. To this end, we are in close contact with the Federal Ministry of Health, as well as with the consumer associations. However, up to now, both institutions are having considerable difficulty with our venture. Although they have now recognised the necessity of such standardisation, there is no direct contact person who is properly capable of contributing to discussions on the topic. The initiators are therefore forced to pursue the long and arduous path of trying to convince the individual federal states and relevant ministries (which have different political compositions) and the consumer protection associations, which are organised on a federal basis, and to unite everyone around a compromise acceptable to all.  
Rotho therefore seeks to represent the various aspects clearly, using self-explanatory icons.
We hope that this answers your questions, and we would like to wish you continued pleasure cooking and heating your meals using our Rotho products.
Our quality assurance department has prepared a table, which is attached.

Our products generally refer to heating, rather than actual cooking. The time required to heat to 70°C is therefore stated.
 
V in ml      400     500     600     700     800     900
Microwave power in W     Heating up time in sec
80     945     1181     1417     1653     1889     2125
150     504     630     756     882     1008     1133
300     252     315     378     441     504     567
450     168     210     252     294     336     378
500     151     189     227     264     302     340
600     126     157     189     220     252     283
800     94     118     142     165     189     213

We would also like to inform you that polypropylene’s melting point is 161–162°C. Also of interest is the glass transition temperature of around 110°C, after which changes can occur to the polymer.

For example, we are working on waste bins which extinguish by themselves in the event of fire. As part of this work, we have made the following observations. The waste bins we tested – by starting a fire in them – extinguished the fires when the lid was closed and the oxygen supply therefore cut off. But a smouldering fire – where the bin melts – is still possible.