With only one ingredient, chips might seem like one of the most basic possible foods.

But these simple slabs of fried potatoes are actually far more complex than you might have thought.

Studies have found that potatoes’ starchy flesh needs to be fried multiple times to get the ideal crunch. 

And, for the best possible results, experts say that you should use Russet potatoes cut to exactly 7cm long and 1.2cm wide. 

So, as researchers search for new way to get even better French fries, MailOnline reveals the recipe for the perfect chip. 

The scientific formula for the perfect chip involves three stages of cooking: once in water, once in cooler oil, and once in hot oil 

The perfect chips, according to science

 

Ingredients 

  • 1kg Russet Potatoes cut into 1.2×1.2x7cm cuboids  
  • 2 tbsp white vinegar 
  • Rapeseed oil (enough to fill your pan halfway up)
  • Salt 

Method

  1. Wash the chopped potatoes under cold running water for four minutes to remove excess starch
  2. Place potatoes in boiling water with vinegar until almost falling apart – between 5 to 10 minutes
  3. Once tender, remove from the water, pat dry with paper towel, and lay out on a baking tray; place this in the freezer for at least one hour 
  4. Heat rapessed oil to just over 325°F (160°C) 
  5. Gently drop chips into the hot oil and cook until firm and lightly coloured – one to five minutes
  6. Remove chips from oil and allow to cool
  7. Increase the oil temperature to 360°F (180°C)
  8. Once the oil is hot, return chips to the pan and cook until a deep golden brown and crispy – around five minutes
  9. Remove chips from the oil and sprinkle with salt immediately 
  10. Serve piping hot 
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Chip science  

The perfect chip has to start with the perfect potato but, to figure that out, we need to start with a quick lesson in chip science.

Potatoes, very simply, contain two things: starch and water.

And, it is the relationship between these two substances that determines whether a chip is a crispy delight or a floppy disappointment. 

Starch is one of the ways in which plants store energy and consists of long chains of carbohydrates.

When potato is raw, these chains are coiled up tightly, making the potato tough and not very tasty. 

But when we drop slices of raw potato into hot oil, the water inside the spud rapidly starts to evaporate and force its way to the surface – which is why chips bubble in oil.

This steam begins to break down the potato cells, turning the long chains of starch into smaller pieces and making the chip soft.

At the same time, hot oil is being forced into the chip, against the force of the steam escaping.

When the starch is hit by the hot oil it undergoes a process called ‘starch gelatinisation’ and becomes a glue-like layer which wraps around the surface of the chip. 

As this outer layer dries out it hardens and becomes crispy, trapping moisture within the interior which then steams the chip from the inside out. 

Dr John Lioumbas, a scientist from the Aristotle University of Thessaloniki, told MailOnline that it is the balance between oil absorption and water evaporation that determines how crispy the chip becomes.

The goal with chip making is essentially to get glue-like layer as thick as possible while avoiding overcooking the interior or burning the outside. 

To achieve this, Dr Lioumbas recommends using a starchier potato.

He told MailOnline: ‘Generally, potatoes with higher starch levels tend to undergo more extensive gelatinization during cooking.’

In his own research, Dr Lioumbas used the Angria variety, but other research suggests that a Russet variety might be best thanks to its high starch levels and good size.

The Russet potato (pictured) is a perfect potato for chips since it has a high starch content and is large enough to cut good sized chips from

The Russet potato (pictured) is a perfect potato for chips since it has a high starch content and is large enough to cut good sized chips from

The Russet potato (pictured) is a perfect potato for chips since it has a high starch content and is large enough to cut good sized chips from 

Preparing your chips  

Now that you have chosen your potatoes, the next thing to do is to chop them into chip-sized pieces. 

In his legendary ‘triple-cooked chip’ recipe Michelin-star chef Heston Blumenthal recommends cutting peeled potatoes into 2cm x 2cm x 6cm rectangles.

However, despite being known for his scientific approach to cooking, Heston may have actually missed the mark here. 

A survey of 2,000 British adults by the Food Advisory Board conducted in 2019 found that the ideal chip was exactly 1.2cm x 1.2 cm x 7cm long

This matters because a smaller chip will not only cook faster but also have a higher surface area to volume ratio. 

In chip terms, this means a more crunchy exterior per gram of potato.

When cooking these at home you should make the chips as long as the potato to avoid wastefully trimming away perfectly good chip-material. 

Once chopped, wash your chips under running water for a few minutes to remove any excess starch which can burn in the hot oil. 

Heston Blumenthal (pictured) is the inventor of the triple cooked chip. He claims that this process produces a chip that is perfectly cooked on the inside and shatteringly crisp on the outside

Heston Blumenthal (pictured) is the inventor of the triple cooked chip. He claims that this process produces a chip that is perfectly cooked on the inside and shatteringly crisp on the outside

Heston Blumenthal (pictured) is the inventor of the triple cooked chip. He claims that this process produces a chip that is perfectly cooked on the inside and shatteringly crisp on the outside 

Heston Blumenthal says that his perfect chips (pictured) should be 2cm by 2cm by 6cm. However, studies suggest that the perfect chip is actually 1.2x1.2x7cm

Heston Blumenthal says that his perfect chips (pictured) should be 2cm by 2cm by 6cm. However, studies suggest that the perfect chip is actually 1.2x1.2x7cm

Heston Blumenthal says that his perfect chips (pictured) should be 2cm by 2cm by 6cm. However, studies suggest that the perfect chip is actually 1.2×1.2x7cm 

Why triple-cook chips?

Triple-cooked chips are cooked once in water and twice again in oil.

This achieves the perfect level of crunch outside and soft inside.

The first boil breaks down the starch and cooks the potato through

The second cook in oil gelatinises the outer layer of starch

The final fry in hot oil cooks the outer layer into a perfect crunchy shell  

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Cooking your chips 

Now that you have chopped and washed your chips, you are finally ready to start cooking.

But getting the perfect chip isn’t as simple as dropping the potatoes into hot oil and being done with it. 

The problem is that to get two different textures of potato – crispy and soft – one temperature of oil just doesn’t cut it. 

Dr Lioumbas explains: ‘When lower temperatures of oil are utilized, the heat transfer occurs at a slower rate. 

‘The slower heat transfer allows for gradual water evaporation from the potato, leading to a softer exterior with less pronounced browning and crispiness.’

Using really hot oil works well to crisp and brown the outside, but risks leaving the interior of the chip uncooked. 

The solution, according to scientists, is to cook the chips three times. 

Once in boiling water, once again in cooler oil, and one final fry in hot oil. 

The first fry in cooler oil sets up the gelatinised-starch structure around the edge of the chip that is then crisped up in hotter oil (stock image)

The first fry in cooler oil sets up the gelatinised-starch structure around the edge of the chip that is then crisped up in hotter oil (stock image)

The first fry in cooler oil sets up the gelatinised-starch structure around the edge of the chip that is then crisped up in hotter oil (stock image)

First, experts recommend that you should boil your chips for anywhere between five and 10 minutes until they are cooked all the way through. 

To ensure they don’t totally fall apart, add a tablespoon or two of white vinegar to the water, as this slows the breakdown of pectin and ensures they retain their structure.

Once the chips are cooked, dry them carefully and lay them out on a tray to rest in the freezer for at least one hour.

While this might seem like an unusual, and time-consuming step, it actually serves two important purposes.

First, the arid conditions of the freezer draw out any extra moisture from the chip that might have been absorbed during boiling.

This means that, when it is time to fry, the outer layers will crisp up quickly and won’t be made soggy by too much water escaping from within.

Secondly, as the potatoes freeze, small ice crystals form which burst the cells holding in the starch.

In testing by food writer J. Kenji López-Alt, this freezing process was found to give chips a distinctly fluffier interior. 

Frozen chips like these might be a great place for cooking inspiration. As they freeze, ice crystals burst the potato cells leading to a fluffier chip, while the conditions in the freezer dry out the surface

Frozen chips like these might be a great place for cooking inspiration. As they freeze, ice crystals burst the potato cells leading to a fluffier chip, while the conditions in the freezer dry out the surface

Frozen chips like these might be a great place for cooking inspiration. As they freeze, ice crystals burst the potato cells leading to a fluffier chip, while the conditions in the freezer dry out the surface 

The next step is to cook the potatoes in a relatively cool pot of oil until they are just beginning to crisp and are light in colour. 

Experts recommend cooking the chips at 325°F (160°C) for between one and five minutes depending on the type of chip.

For the best results, use a neutral oil with a high smoke point such as rapeseed or groundnut oil which will let you reach high temperatures without imparting an oily flavour. 

This first cook sets up that thick layer of gelatinised starch that holds the chip together and is prepared to become the crispy exterior. 

Mr López-Alt says this extra stage is necessary because boiling water doesn’t have the energy to drive excess water out of the potato and get that thick crust we want.

The rate of heat transfer during frying is linked to the dynamics of vapour bubbles formed on the potato surface,’ he explained.

‘When the temperature of the frying oil increases, the heat transfer becomes more rapid. This accelerated heat transfer results in quicker water evaporation from the potato.’

In fact, this relationships between bubbles and oil is so important that Dr Lioumbas suggests that the perfect chip would be literally out of this world. 

He says: ‘Fries tend to cook more efficiently in hypergravity due to alterations in gravitational forces affecting buoyancy forces and the vapor dynamics on the potato surface during frying.’

The ideal place to cook chips, he suggests, would be the surface of Jupiter since the intense gravity would speed up heat transfer and produce crisper chips.

Jupiter (pictured) would actually be the best place to cook chips since high gravity speeds up the transfer of heat from the oil to the potato, ultimately resulting in a better chip

For those of us who can’t quite spare the time for a trip to Jupiter, Dr Lioumbas recommends using a centrifuge.

He said: ‘By creating increased gravitational acceleration forces within the fryer environment, similar to those experienced in hypergravity settings, it’s possible to optimize the frying process and achieve superior French fry quality.’

However, until hypergravity friers become commercially available, most home cooks will still have to follow the two stage frying process for the best results. 

Having fried your chips once (on Earth) and allowed them to cool, it is now time for one final fry at a higher temperature. 

This high-heat cook transforms the gelatinised layer into a dry, crispy crust that gives the chip its satisfying crunch.

Once the chips have been through their third and final stage of cooking they should be light brown and shatteringly crisp (stock image)

Once the chips have been through their third and final stage of cooking they should be light brown and shatteringly crisp (stock image)

Once the chips have been through their third and final stage of cooking they should be light brown and shatteringly crisp (stock image)

The heat also promotes the Maillard reaction, a chemical reaction between sugars and amino acids responsible for the browning you might recognise on a seared steak.  

Dr Lioumbas explains that the high heat is responsible for ‘promoting a more efficient Maillard reaction and caramelization process on the surface.’ 

He adds: ‘Consequently, the crust becomes crisper and exhibits a deeper golden-brown color due to the enhanced development of desirable flavor compounds associated with the Maillard reaction and caramelization.’

So, to get the best out of your chips, crank the heat of the oil up to 360°F (180°C) and drop in the chips.

After about five minutes the chips will be a light golden brown and beautifully crisp.

When they are ready, pull them from the oil and toss them with salt immediately so it sticks to the hot oil.

Then, at long last, you will finally be able to enjoy a scientifically perfect chip. 

This post first appeared on Dailymail.co.uk

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