The first potatoes to be fried in space will have a… Greek signature. Quite fitting, one might say, since for some the now “international” “fryer” has its roots in the ancient Greek “frygitron”, a deep pan-like vessel in which our ancestors roasted barley. However, the issue is not etymological. This is the idea of a group of researchers from the Aristotle University of Thessaloniki (AUTH) that was enthusiastically adopted by the European Space Agency (ESA).
The usefulness of the "space potato" is not limited only to the obvious but rather overly limited effect of allowing astronauts to eat something on their long-distance missions that will remind them of home and improve their psychological state and performance, alleviating their hunger and loneliness (Russian cosmonaut Sergei Volkov, who recently made a relevant statement upon returning from the International Space Station, is not the only one who has expressed a desire for such a "homemade" meal). The seemingly trivial act of frying a potato hides previously unknown mechanisms that can find valuable "space" uses in improving heat exchangers and fire protection of spacecraft and beyond. They can also have "earthly" applications, offering healthier and more energy and time-efficient products to one of the largest sectors of the food industry. Finally, on a more personal and everyday level, they can teach us the secrets to perfect frying.
Operation "space frying pan"
These are precisely the secrets that are beginning to be revealed. The results of the first two phases of the experiments that have been carried out so far in conditions of terrestrial gravity and hypergravity have surprised the world of science and industry because they have revealed completely new parameters in the "frying pan" business. First, they found that the orientation of the potato - whether it "floats" horizontally or vertically in the oil - is of decisive importance for how quickly it is fried, how much crust it forms and how much oil it absorbs, knowledge that on an industrial and domestic level can offer energy and time savings as well as crispier and less fatty potatoes. More findings are expected in the next phase, when Greek experts will fry in conditions of weightlessness, in a parabolic flight that will take place no later than the summer of 2014. But let's start from the beginning.
A potato fried in hot oil is a porous medium that reacts at very high temperatures, and porous materials are one of the latest “cutting-edge” areas being studied to improve heat transfer devices – devices used to quickly remove large amounts of heat to points where high temperatures develop. In this context, the European Space Agency is funding five research groups that are examining boiling phenomena in various materials. One of them is the group from the Department of Chemistry of the Aristotle University of Thessaloniki, led by Professor Thodoris Karapantsios. “It has been funding us for the last three years to study the phenomena of heat and mass transfer with simultaneous phase change in porous media. Particular importance is given to the comparison between artificial porous media, such as ceramics or polymers, and natural porous media,” the professor says, speaking to “Vima”. "We told them that we would like to examine the evolution of the porous structure of potatoes during frying as a natural porous medium because this is important for the food industry and technology, and they found the idea very attractive."
The fried potato from the inside
The result is that Greek researchers will be the first on the planet to fry in zero gravity conditions. Although frying is a very basic process for the study of heat and mass transfer, it seems that no one has examined it systematically until now. Thus, the AUTH team, in its series of experiments, which have been underway for three years, has achieved many firsts, “testing” the relevant models for the first time and frying a material for the first time in hypergravity conditions at the ESA Large Diameter Centrifuge (LDC) in Noordwijk, the Netherlands last summer. For all the studies, the head of the experiment, Yiannis S. Lioubas, has developed a special experimental setup that allowed for the first time precise measurements not only on the surface of the potato but also inside it. "The most difficult thing we achieved with this device was that we were able to measure just below the surface of the porous medium with an accuracy of a fraction of a millimeter," says the researcher. "And at the same time we filmed the bubbles on its surface with a high-speed camera.
Thanks to the experimental setup, which varied the inclination of the potato (at 0, 90 and 180 degrees) and having insulated the sides of the potato that they did not want to examine, the researchers were able to record the formation of bubbles, the temperature and a series of other data (30 per second, as Mr. Karapantsios tells us) that allowed them to follow in every detail what was happening throughout the frying process. “We were able to record the violent removal of moisture that, as it receded, left behind a labyrinthine porous structure, known as a crust, whose thickness initially grows rapidly but then more and more slowly during frying – things that until now we had assumed or only had a more general qualitative view of. And it is the structure and thickness of the crust that significantly determines the final penetration of the oil and therefore the nutritional load of the potato," he explains.
Grandmothers and fryers
The first surprising observation in the phase of the experiments carried out in 1 g conditions – that is, in Earth's gravity – was that a potato that is "sizzling" in oil does not fry in the same way on all sides. The sides that are perpendicular to the bottom fry faster and form a thicker crust than the upper horizontal side, while the lower horizontal side becomes rather boiled, since it forms almost no crust. This is because, as the researchers saw, due to the buoyancy, the steam bubbles that are created (for gastronomy the difference can be huge, but for Physics, frying is essentially boiling, only it is done in oil and at higher temperatures) "stick" to it and act in a way as a thermal insulator. So the secret to fast, crispy potatoes is to place them vertically in the oil. "The more vertical the potato is, the faster it will fry – which means saving energy and time – and the crispier it will become since its crust increases," says the professor.
In real life, of course, outside the laboratory and the researchers' special experimental setup, potatoes rarely stand upright in the oil, and our grandmothers who fried them by constantly turning them over prove to be wise. This is the advice that the scientists of the Aristotle University of Thessaloniki are giving today for "domestic" use, while for industry they are proposing mechanisms that will create a gentle agitation by changing their inclination. After the recent publication of two relevant studies in the "Journal of Food Science", an American company that manufactures fryers got in touch with Mr. Carapaccio: the idea is to equip its fryers with systems that will adjust the inclination of the potatoes depending on how crispy each person wants them, but as the professor told us, this is something that they have not yet examined.
On a more theoretical level, the researchers also managed to experimentally verify for the first time the recent overthrow of an old theory about frying. “Until recently, scientists had the impression that the potato crust was identical to a water evaporation front – that, that is, the water retreats abruptly like a front towards the interior of the potato and as it retreats, the crust is formed at the same time,” explains the professor. “A few years ago, however, American researchers from Cornell University showed with a theoretical model that this is not the case, that the process does not occur abruptly, like a front, but over a wider area, like a zone. "Our experiments showed for the first time that their theoretical model for the evaporation zone is valid and furthermore that this evaporation zone is narrower the higher the oil temperature, so at very high frying temperatures (180 degrees Celsius) it can – under certain conditions – be considered to be approaching an evaporation front.
Precious centrifuge!
The second phase of the frying experiments in hypergravity reached the very “heavy” conditions of 9 g – a gravity nine times greater than that of Earth. When gravity increases, frying becomes more intense, meaning that, although the temperature of the oil is the same, heat is transferred at a faster rate, offering a good way to “test” theories and models. The evaporation zone theory passed the test here too, while the researchers examined another important factor. The force of g, as Mr. Karapantsios tells us, is included in all industrial models that describe the transfer of heat from the oil to the body being fried. “This dependence, the relationship of heat transfer with g, had never been tested, because no one had ever done experiments in hypergravity,” he explains.
As for the most attractive aspect for a non-scientist, the potato itself, it seemed to reach its… peak under the “heaviest” conditions. Higher gravity and more intense heat transfer mean much smaller bubbles, much faster frying and potatoes with a thicker crust and less oil – and this was theoretically expected. But what the experts discovered was that there is an optimal limit here, 3 g. “After 3 g, at 6 or 9, there is a small improvement, in times and crispiness, but not so impressive,” says the professor. “The bubbles are smaller, but as we saw with the crater, the imprint they leave on the potato by forming the crust does not change.
This means that a fryer equipped with a small centrifuge system could significantly reduce frying time, offering crispier, healthier and less fattening fries. Mr. Karapantsios estimates that the different porosity of the crust in “centrifuged” fries could lead to a 15%-20% reduction in their oil content, but the relevant measurements will be made in the near future.
Crispy and healthier
If we exclude the advanced technology of centrifugation and the special device for measurements, the experiments could be a foodie’s delight: the scientists used “real”, fresh and not pre-fried potatoes, which they fried in olive oil, in the traditional Mediterranean way. “The idea is that the astronauts will not take two tons of pre-fried potatoes with them. They will grow potatoes themselves either on the transport ship, if there is space, or at their destination,” says Mr. Karapantsios. “However, on a practical level, most of us fry raw potatoes at home. For the industrial sector, where pre-fried potatoes are mostly used, our experiment is a reference experiment, since it studies the conditions in the primary, unprocessed product.
And what about the taste? We cannot have an official answer to this question at the moment. As the professor explains, in order to make a scientific judgment about the taste, one would have to consult a panel of experts, and there are no expert tasters for fried potatoes in Greece. In addition to an effort to train a team at the Aristotle University of Thessaloniki, there are also thoughts about collaborating with experts from abroad. “However, if you want me to tell you as an amateur, the potato is the same potato that we know, only it is crispier,” he tells us. “And for me, it is an advantage that it has less oil.
Do you fry in microgravity?
In the next phase, frying in zero gravity, the researchers do not expect to taste delicious potatoes. This is because in these conditions the potato will not be fried. “What we expect to see is what happens in the conventional frying pan with the bottom horizontal side: because there is no gravity the potato will be trapped in a huge bubble,” says Mr. Karapantsios. “But we are not concerned with whether someone can fry in microgravity. The answer is no.” What concerns them – beyond the problem of the astronauts’ “menu”, which will probably be solved with a centrifuge system – is to study frying in these completely unknown conditions and to understand its mechanisms in order to use their knowledge to improve, not only our dish, but also the durability of ESA spacecraft.
“Frying as a mechanism for removing water from porous media with intense heat transfer rates is of interest for boiling heat exchange systems that are often used in space,” explains Mr. Karapantsios. Also, as Mr. Lioubas points out, many processes in space involve heat and mass transfer in porous media, with the most familiar example being the entry of spacecraft into the Earth’s atmosphere. “Due to friction,” says the researcher , “very high temperatures develop in the shell in front of the nose and many spacecraft have been destroyed during their entry into Earth. Perhaps we could produce better materials to avoid these disasters.” The possibilities do not end here. "You know, no matter how much someone fries a potato, even until it burns on the outside, a part of it inside always stays fresh because it is protected by the crust that is created," he adds. "This is very important because it shows us a biomimetic approach. Nature shows us how to exploit phenomena in our own applications.
Fire in Space
A fire in zero gravity is very different from the fires we know here on Earth. "A few years ago the European Space Agency did a simulation and saw that inside a spacecraft, because there is a lot of oxygen, the fire spreads very quickly, while due to the lack of gravity it does not spread in the usual way, it does not spread everywhere, but diffuse pockets of fire are created in space," describes Theodore Karapantsios. In these cases, the astronauts have 60 seconds to reach the hatch, open it and get out. This time, as the professor explains, is very short, while due to the fire it is very likely that the walls of the ship and the hatch will be so hot that they cannot even touch them.
A fire in zero gravity is very different from the fires we know here on Earth. "A few years ago the European Space Agency did a simulation and saw that inside a spacecraft, because there is a lot of oxygen, the fire spreads very quickly, while due to the lack of gravity it does not spread in the usual way, it does not spread everywhere, but diffuse pockets of fire are created in space," describes Theodore Karapantsios. In these cases, the astronauts have 60 seconds to reach the hatch, open it and get out. This time, as the professor explains, is very short, while due to the fire it is very likely that the walls of the ship and the hatch will be so hot that they cannot even touch them.
"To keep the temperature of the walls and the hatch low," he adds , "we have proposed, and we are studying this, to flood the interior with water, and indeed with the spacecraft's sewage, not the clean water that the astronauts use. The walls and the hatch are made of porous materials and the water will be channeled inside them, so the boiling that will occur will reduce their temperature, giving extra time for the astronauts to get out.
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