What is the chemistry behind roast potatoes

The potato - or Solanum tuberosum L. - is part of the nightshade family. The vegetative and fruiting parts of the potato contain the toxin solanine, which is hazardous for human consumption.

When growing potatoes, it is therefore essential to wait until the plants die off before digging the potatoes up. Green potatoes should not be eaten, but small amounts of potato juice are used in medicinal practices, including the treatment of peptic ulcers and relief from pain and acidity.

A poultice made from boiling potatoes in water is also known to alleviate the pain of rheumatic joints, swellings, skin rashes and even hemorrhoids. Uncooked potatoes can also be utilized as a soothing plaster for scalds and burns.

A potato is a tuber, meaning this can be planted in soil to grow more potatoes. As the potato is technically alive, even when dug up, the first step towards roasting a potato is to inactivate the enzymes contained within that allow the potato to function as a tuber.

Different types of potatoes are better suited for specific cooking methods; for example, in the UK, it is common to use the Maris Piper variety for roast potatoes, while this is generally the Russet potato in the United States.

The cells inside all varieties of potatoes have the same basic structure. Each cell includes a nucleus, a sack of water, and a number of other structures related to the cells’ functions.

Each cell also features a wall that protects the inside, and these cell walls keep the potato firm via a phenomenon known as ‘turgor.’ Water within the cells presses against their walls, meaning that if the potato dries out and loses its moisture, this firmness is lost.

Solanine: toxic effects seen at 1000 MC/KG of body weight.

Solanine: toxic effects seen at 1000 MC/KG of body weight. Image Credit: Asynt

Cooking the potato causes this cell wall to rupture and prompts the starch grains to swell and disperse. Chemically speaking, this process leads to the cooked potato’s soft and fluffy center.

The greater the surface area of the potato in contact with the roasting pan, the more opportunity there is for it to become crisp. Researchers at a UK school discovered that the optimum approach involved cutting the potatoes at 30° angles, increasing their surface area far more than the typical 90° cuts.

Par-boiling potatoes for approximately 10 minutes in salted water with ½ teaspoon of baking powder helps break down starch. The potatoes are then drained and agitated to loosen their rigid edges and allow steam to dissipate.

A group in the US investigated the impact of the water’s pH on the roast potatoes’ end results, discovering that using a ‘regular’ or slightly alkaline water resulted in the best end product.

In contrast, more acidic water resulted in hard, chewy roast potato.

The act of roasting the potatoes is based on the Maillard reaction – a reaction that takes place between proteins and sugars.

The higher the cooking temperature, the faster this reaction proceeds. It is, therefore, advisable to cook the roast potatoes for a shorter time at a higher temperature than a longer time at a lower temperature.

Tumbling the par-boiled potatoes in either pre-heated or cold oil and adding seasonings or flavorings is also key to this process. The choice of oil or fat is mainly seasonal or based on personal preference, but this does impact the cooking process.

Flavorful fats like duck or goose fat have a much lower burning point than vegetable or sunflower oil, potentially leading to overcooked potatoes. The addition of oil with a higher burning point will help stabilize this reaction.

Potatoes should be afforded ample space to ensure even cooking, with at least one side resting fully on the base of the pan. These are typically cooked for 20 minutes before being turned over and cooked for a further 20-30 minutes.

Following and applying the science makes it possible to achieve perfect roast potatoes.  At Asynt they believe that chemistry is like cooking - just don't lick the spoon!

About Asynt

Asynt was formed in July 2003 with the aim to develop, supply and support new, sustainable and novel products central to the laboratory.

Since inception, they have developed the DrySyn range (a clean, safe alternative to oil baths and heating mantles) both reducing costs in purchasing / disposal of oil and a 35% reduction in energy consumption.

They also take pride in reducing laboratory water consumption using their air cooled CondenSyn units and highly effective water circulators.

The current team has over 70 years of experience in the scientific sector and work hard to help their customers find the best possible solutions for their requirements.

Key product lines available include Asynt ReactoMate Controlled Lab Reactors, the DrySyn heating and cooling blocks, and tools from Grant, IKA, Julabo, Huber, Porvair, Telstar and Vacuubrand amongst others. With a broad range of scientific equipment and consumables ranging from bench top laboratory scale to pilot plant and beyond both in the chemical and biological sectors.

Asynt’s Managing Director, Martyn Fordham, spent almost twenty years dealing with the requirements of research chemists (at the outset just custom glassblowing) before forming Asynt. For Martyn, having the right staff who are both knowledgeable and dedicated to customer support has been the key to Asynt’s successful growth.

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Last updated: Apr 21, 2022 at 1:03 PM


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