Vacuum-fried: how our vegetable crisps are made

Our bags say "vacuum-fried". It sounds technical, but the idea behind it is simple physics. It explains why our beetroot crisps come out deep red and our carrot crisps orange, rather than brown.

What happens when you fry

Vegetables are mostly water. For a thin slice to turn crisp, that water has to go. In an ordinary fryer this happens at around 170 to 180 degrees: the water evaporates and the slice becomes dry and firm. At that heat, though, the sugar in the vegetable browns heavily, and much of the colour and natural flavour is lost.

What the vacuum changes

The boiling point of water depends on air pressure. At sea level it is 100 degrees; high up a mountain it is noticeably lower. Vacuum frying puts this effect to work: the fryer is sealed and the pressure inside is lowered a lot. The water in the vegetable then evaporates at a much lower temperature, and the oil does not need to be as hot as in an open fryer.

The result is a slice that still turns crisp but has taken less heat. Three things matter most to us:

• The colour stays. Beetroot stays deep red, carrots stay orange. We need no colourings to get there.

• The taste stays recognisable. Beetroot is earthy and slightly sweet, carrot mild and sweetish. That is why no artificial flavourings are needed.

• The slices turn crisp without burning. Sugary vegetables like beetroot quickly turn bitter in hot oil.

Fried is still fried

Vacuum frying is frying, just at lower pressure. Our crisps do come into contact with oil, and we say so. What is different is the temperature, and you can tell from the colour and the taste.

Where we do it

Our beetroot and carrots grow on a farm in Iffwil. They are vacuum-fried and packed in Siselen by M. + R. Schwab AG, about 28 km away. Both places are in the canton of Bern. If you want to try the crisps, you can order them in the shop from three bags: beetroot, carrot or mixed.