Chips with everything – except fat – University of Reading
08 May 2001How does fat get into chips during frying? Well, it doesn't. This surprising find comes from research by Professor Leo Pyle and PhD student Pedro Bouchon in the University of Reading's School of Food Biosciences. Their work has shown that 95% of the fat or oil which ends up in your chips is absorbed once the hot chip has been removed from the oil. Why? Because, despite appearances, frying is really another way of boiling potatoes.
When the chip is immersed in hot (not boiling!) oil, it heats up and when its surface is hot enough the moisture in the chip begins to boil off. This creates a moving interface or evaporation front in the chip, separating two very different regions: the crust and the core. This composite structure is very important: most of the pleasure in eating fried foods (apart from licking your fingers) is due to the sensation of biting into a dry, porous, crispy outer layer surrounding a cooked (boiled) interior. In fact, hardly any oil is taken up into the chips during frying time.
It's a different story once the chips are removed from the oil. The chips carry oil with them on their surface. This oil can do one of three things: it can evaporate (at the temperatures in question, this is negligible); it can drain off; or it can be sucked into the porous crust region – which is approximately .5 – 1 mm thick – by capillary forces. Capillary suction can't begin until the inside of the chip has cooled sufficiently for evaporation to stop: until then steam still provides a barrier to prevent oil uptake. Once this point is reached, oil can rush in to (more or less) fill the pores. All this work involves some pretty hard science. With Dr Peter Hollins (Chemistry) the Synchotron source at Daresbury was used to get the first ever measurements of the oil distribution in the crust Understanding how oil is taken into up chips gives important clues about how to minimize it – that is , how to make a low fat chip. In the end, of course, the proof of the chip is in the eating &ellipse;
For further details, please contact Sue Rayner or Carol Derham, Tel: 0118 931 8004/5, Fax: 0118 931 8924