Why some potato chips brown and others don’t – Potato science

If you’ve ever made any potato dish you might have had both great success and failures with the exact same recipe. In some cases the fries just turn out perfect, in other cases they brown way too quick. Your mashed potatoes may turn out super smooth one day and be chalky the other.

Chances are that your recipe is perfectly fine, but that you’re using the a different type of potato or that you didn’t store your potatos properly. That’s the beauty (and challenge) of using natural products. They’re never identical and all have their own properties.

Mealy vs waxy potatoes

Most of you will have heard of mealy vs. waxy potatoes. These description refer to the texture of potatoes. Mealy potatoes refer to potatoes that are drier whereas waxy potatoes have a smoother mouthfeel. Even though this distinction is not very precise, it is a first way to distinguish different types of potatoes.

Whether a potato is mealy or waxy depends on the variety of potato itself and not as much by how it’s stored.

It’s all about the starch

So what do the terms refer to? The terms refer to the type of starch that the potato is made of. As we discussed before when talking about cooking potatoes, potatoes contain a lot of starch. Starch again mostly consists of two types of molecules: amylopectin & amylose.

So what differs a waxy from a mealy potato? Interestingly, researchers have not reached full agreement on this. It seems to be a combination of starch content as well as how a potato is build up, cell sizes and how cells are attached to one another. Generally, it seems that a higher starch content gives a more mealy potato. Mealy potatoes also tend to have larger cells and the cells don’t break down as easily either. For waxy potatoes on the other hand starches leak out of the potato cells. However, not in all cases do these principles hold up.

Tip: if you would like to see very nice detailed microscope photos of potatoes, have a look at the article by McComber, mentioned at the bottom of this post!

fried potatoes - brown and light ones
These potatoes apparently don’t have that much sugar seeing how yellow they are after frying.

Colour of potaoes

The second aspect of potatoes that can vary a lot is the colour of the baked or fried potato. Some potatoes turn brun very easily, whereas others remain yellowish, even if they’ve been in a deep frier for a long period of time.

Sugar, the Maillard reaction and browning

These colour changes very much depend on the sugar content of your potato. The browning that occurs when your frying potatoes is caused by the Maillard reaction which is a reaction between sugars and proteins in food. It accelerates at higher temperatures and for higher concentrations of proteins and sugars. So, if a potato contains more sugar it tends to brown more quickly. (The amount and type of protein present tends to impact browning as well, however, the role of sugar seems to be a lot more important.)

Factors that impact sugar content

There are a lot of factors that influence the sugar content of potatoes. Some depend on the variety of potato you’ve chosen, others are impacted by growing conditions (e.g. temperature in the ground).  The category consumers and manufacturers have most control over though are the storage conditions.

First of all, mechanical actions such as cutting, slicing and tumbling potatoes can increase the sugar content of some varieties. Second, probably one of the most important ones, is the storage of potatoes at temperatures below 10C or over 20C. At these temperatures the content of sugar increases quite rapidly.

At some point in time potatoes will start to sprout. At the onset of this process sugar content tend to be very high since the new sprouts need the energy to grow.

Just like other plants, potatoes respire and continue to do so for a long time after harvest. The higher the respiration rate, the higher the sugar content. So by limiting the respiration rate the sugar production can be slowed down. Temperature is one way to do this, but controlling the gas composition of the air is another way. At a lower oxygen concentration or increased carbon dioxide concentration respiration is generally slowed down.

How to get very brown potatoes

In most cases producers want to limit the amount of sugars in potatoes so they can be stored for longer and don’t discolour too much. But what if you find your potatoes don’t brown fast enough? You could try storing them in the fridge for a couple of days! The cool temperature in the fridge should increase the sugar content and thus improve the brown colour.

Fun insight: Which colour you prefer seems to be culturally dependent! Whereas in the Netherlands a good fried potato tends to be a nice light brown colour those in the US for example remain a lot lighter in colour, if they brown at all. Have a look at fast food advertisement, most of them show yellow and not brown fries.

Sources

On the difference between waxy and mealy potatoes, Cooking Science Guy

Marle, N. van, Characterization of changes in potato tissue during cooking in relation to texture development, (1997), http://edepot.wur.nl/200362#page=36

Gupta, V. K., Luthra, S. K., & Singh, B. P. (2015). Storage behaviour and cooking quality of Indian potato varieties. Journal of Food Science and Technology, 52(8), 4863–4873. http://doi.org/10.1007/s13197-014-1608-z

DINESH KUMAR*, B P SINGH and PARVEEN KUMAR, An overview of the factors affecting sugar content of potatoes, 247Ann. appl. Biol. (2004), 145:247-256

McComber, Diane R.; Horner, Harry T.; Chamberlin, Mark A.; and Cox, David F., “Potato Cultivar Differences Associated withMealiness” (1994).Botany Publication and Papers. 55. http://lib.dr.iastate.edu/bot_pubs/5

Narpinder Singh, Lovedeep Kaur, Rajaranganathan Ezekiel and Harmeet Singh Guraya, Microstructural, cooking and texturalcharacteristics of potato (Solanum tuberosumL) tubers in relation to physicochemical andfunctional properties of their flours, (2005), Journal of the Science of Food and AgricultureJ Sci Food Agric85:1275 – 1284 , DOI: 10.1002/jsfa.2108


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