raw potatoes

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

If you’ve ever made any potato dish you might have had both great successes and failures with the exact same recipe. In some cases the fries just turn out perfect, in other cases they brown way too quick and burn.

Chances are that your recipe is perfectly fine, but that you’re using the a different type of potato or potatoes that were stored differently. These can result in huge differences between the outcomes of your potato dish. That’s the beauty (and challenge) of using natural products. They’re never identical and all have their own properties. For potatoes, the amount of browning and its texture, are the most important variables.

Here we’re discussing colour only, but if you’re curious about the texture/smoothness, we’ve written about that here!

Colour of potatoes

When you bake or fry potatoes, one of the most obvious success criteria of your fry, chip or baked potato pieces is its colour. Whether you’re looking for a nice brown colour or actually a more pale yellow. Of course, how you prepare your potatoes will impact the colour, whether you heat them at very high temperatures, or still pretty mild for instance. But don’t forget the importance of choosing the right potato. Some potatoes simply turn brown very easily, whereas others remain yellowish, even if they’ve been in a hot deep fryer for a long period of time.

Their are a few mechanisms at play here!

Sugar & the Maillard reaction

One of the main browning mechanisms that occurs when you prepare your potato is that famous Maillard reaction. This is a very common reaction between reducing sugars (e.g. glucose, lactose) and proteins in food. There are several ways to control the Maillard reaction.

By controlling the amount of sugar and proteins you can get more of the reaction going on. More sugars will lead to more browning and as we’ll discuss further down, there are a lot of ways to control the sugar content of a potato, whereas you’re more limited when it comes to the proteins.

The other controlling factor is the temperature + time. At higher temperatures the reaction goes a lot faster, thus it browns more quickly. At lower temperatures it goes more slowly, which will give you a chance to cook the inside well (as you do when making french fries)!

As a result, if a potato contains more sugar it tends to brown more quickly. The same goes up for cakes, bread and other baked goods. 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, especially for our potatoes.

So, if you want your fry to brown well, you want a slightly higher sugar content than if you’re looking for a more yellow/pale potato colour. That said, you never want the sugar content to be too high. This will result in a burned potato before you even get a chance to cook the inside.

Enzymatic browning

Browning can also be caused by a reaction caused by enzymes. Enzymes are proteins and will be broken down by the extreme heat, however, they can result in browning at the start. A good proof for this mechanism being important is that blanching potatoes (quickly boiling them before frying) prevents a lot of browning of fries! Since enzymes are broken down by heat, this heat treatment will prevent any of this browning.

freshly fried crispy fries in sunflower oil
Apart from the brownish skin, these potatoes are pretty yellow still (and very crispy!).

How to get very brown potatoes

So now that we know of the role of sugar in potatoes, you’ve got a few ways to control the amount of browning. Using one of the methods described above to increase or decrease the sugar content will change the amount of browning for sugar.

But there’s more!

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.

Factors that impact sugar content

When you want to increase browning through the Maillard reaction, it’s all about increasing sugar content. So how can you control for the sugar content of a potato?

Potato type

There are a lot of factors that influence the sugar content of potatoes. It depends on both the potato you’re using as well as on how you’re using this potato. Different varieties naturally contain different amounts of sugar. But it is also impacted by its growing conditions (e.g. temperature in the ground). Apart from choosing a potato type that you know works well, there is very little else you can do here as a consumer. As a manufacturer though, you can request or analyze the sugar content of your potatoes.

raw potatoes
These potatoes are sprouting already which means their sugar content is probably quite high!

Storing

Another category consumers and manufacturers have good control over are the storage conditions. Storage of potatoes at <10C or >20C results in a rapid increase of reducing sugars in the potato. So, store it at moderate temperatures, approx. 10-20C. Even if it was previously stored at higher or lower temperatures, storing it at this range for a while will restabilize the potato.

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.

If you store potatoes for too long, they may 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. Therefore, sprouting potatoes will brown more quickly.

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. So this helps prevent additional sugar from forming.

Processing

Last but not least, how you treat your potato will of course impact the amount of sugar in the potato! Mechanical actions such as cutting, slicing and tumbling potatoes can increase the sugar content of some varieties.

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

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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