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Water – the Main Architect of Crispness

A fresh potato contains around 75–80% water, which is why the first and most important process taking place during frying is its rapid evaporation.

Once chips are immersed in oil heated to approximately 175–190°C, the surface of the potato very quickly reaches a temperature exceeding 100°C. The water present in the outer layers rapidly changes into a gaseous state, and the resulting steam escapes to the outside

– explains Dr inż. Paulina Bartos.

This process leads to the formation of a thin, dry and porous layer on the chip’s surface. The microscopic pores left behind by escaping steam make the outer layer rigid and brittle. When it breaks simultaneously in many places during eating, we hear the characteristic crunch.

From a scientific point of view, this is the effect of the mechanical properties of a material with a very low water content

– adds the researcher.

Starch – Nature’s Structural Engineer

The second key component of a potato is starch, which consists of two polysaccharides: amylose and amylopectin. At temperatures of around 60–75°C, starch granules absorb water and swell in a process known as gelatinisation. As a result, the inside of the chip becomes soft, delicate and fluffy.

The situation on the surface is entirely different.

In areas where water evaporates intensively, starch becomes dehydrated and forms a compact, rigid network. During cooling, starch undergoes partial retrogradation – a process involving the reorganisation of polysaccharide chains. This further strengthens the structure of the crispy outer layer 

– says Dr inż. Bartos.

The Maillard Reaction – the Chemistry of Flavour and Colour

The golden colour of chips is produced by one of the most fascinating chemical reactions that takes place in the kitchen – the Maillard reaction.

It usually begins at temperatures above approximately 140°C, when reducing sugars react with amino acids present in potato tissues. This is not a single reaction but an entire cascade of transformations leading to the formation of hundreds of new chemical compounds. Among them are volatile substances responsible for the characteristic aroma of fried chips, as well as their golden-brown colour

– explains the chemist.

It is the Maillard reaction that makes freshly fried chips smell so appetising. The same processes are also responsible for the aroma of freshly baked bread, coffee and roasted meat.

Why Are Chips Fried Twice?

Professional chefs have long been applying knowledge derived from the physicochemistry of food. The first stage of frying, carried out at a lower temperature (approximately 150–160°C), allows the potato to heat evenly and enables complete starch gelatinisation inside. The surface remains relatively pale and flexible.

The second frying stage, at around 180–190°C, causes the rapid evaporation of the remaining surface moisture and intensifies the Maillard reaction. As a result, a thin, exceptionally crisp outer layer is formed while the inside remains soft. The result is a thin, exceptionally crispy outer layer while maintaining a soft centre

– adds the researcher.

Not Every Potato Produces the Perfect Chip

The quality of chips is also determined by the chemical composition of the potato itself. The best varieties for frying contain high levels of starch and only small amounts of simple sugars. A higher starch content promotes the formation of a fluffy interior, while a limited amount of sugars prevents the surface from darkening too quickly.

This is why potatoes stored in a refrigerator are not recommended for making chips. At low temperatures, some of the starch breaks down into simple sugars. During frying, these sugars intensify the Maillard reaction, causing the chips to darken more rapidly. At the same time, higher amounts of acrylamide – a chemical compound considered potentially harmful to health – may be formed

– notes Bartos.

Chemistry in Every Bite

Interestingly, the same chemical principles apply not only to traditional potato chips. Chips made from sweet potatoes, carrots, parsley root, celeriac and courgettes are becoming increasingly popular. Each of these vegetables differs in its content of water, starch, sugars and fibre, which is why they behave slightly differently during frying or baking.

Regardless of whether we choose classic potatoes, sweet potatoes or less obvious vegetables, success always depends on the same principles: selecting the right temperature, effectively removing excess moisture and applying the appropriate cooking time. After that, all that remains is a pinch of salt and your favourite seasonings – because while chemistry creates the perfect chip structure, it is the seasonings that give it its final character.
 

Source: Dr inż. Paulina Bartos

Edit: Kacper Szczepaniak, Centre for Brand Communications, 91ÌÒÉ«