Please the fry lovers in your life by mastering the homemade french fry.

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Every child knows the loophole. Chips (or fries in North America) are technically a vegetable. They’re made from potatoes, aren’t they? But every child also knows that fries don’t taste like a vegetable; they taste like the reason God created oil and salt.

We all need to eat vegetables. The Australian dietary guidelines recommend 5 to 6 daily servings. But most children, my own included, would be happy to fill those servings with chips, the better vegetable.

It’s up to us adults to moderate the foolish impulses of our young but I suspect it’s not just children using the chip loophole. Over a third of all potatoes produced in Western countries end up as fries. The kids can’t be eating all those chips on their own.

There is a hypothetical post where I talk about the dire health implications of eating all these chips. But we can get that anywhere. What I want to talk about today is how to increase our supply by making fries in our own homes.

For the home cook the problem is that we all know what a good fry looks, and tastes, like. Most restaurants do a pretty good job of making fries. But restaurants have fancy equipment that makes the job a lot easier. Making a good chip is much more of a challenge for us cooks working in our home kitchen.

Us home cooks need some help, we need some science.

The Anatomy of a Potato

Our quest for good home fries starts, of course, with the potato. God’s gift to fast food restaurants. The potato is an example of a tuber, a storage structure that develops from the stem or root of some plants.

Tubers are a form of asexual reproduction for the plant, they are capable of developing into a whole new clone of the parent plant. To support the growing clone the potatoes are stuffed with starch and it is this starch that makes the potato such a delight when fried.

Dont eat green potatoes

From the plants perspective potatoes are not really meant for consumption by other organisms. They are the future of the plant after all. Unlike fruits, which plants want us to eat, plants will often produce chemicals in parts of the plant that they don’t want eaten.

Potatoes are an example of this and they contain significant levels of alkaloids that are intended to deter insects and herbivores from eating them.

Considering the amount of potatoes that are eaten world wide, the strategy didn’t work too well when it came to humans. But under stressful conditions and high light levels the amount of these chemicals in a potato can triple becoming potentially toxic to humans.

As light also induces chlorophyll formation if a potato is green we can use it as a proxy for toxin production. So, if your potato is green either throw it out or peel all the green bits off.

You’ll often see some greenness about your potato if you leave it in the cupboard too long though at a few supermarkets I’ve bought potatoes that had been pre-greened, very disappointing.

Another thing we need to know before we start frying is that the cells of a potato have a cell wall. All organisms are made up of cells but plants differ from animals by having this durable, but flexible, wall around there cells (I go into this more here).

For our future chip, the cell walls of the cells towards the surface of the chip will contribute to the crunchy exterior of our fry.

Waxy vs. Starchy Potatoes: Which Makes Better Fries?

If we’re going to get a good fry we also need to pick the right potato and there are a lot of different types of potatoes. What we want, though, is a starchy potato.

A starchy potato, like a Russet, is a potato variety that has more starch than a waxy potato, like a Cherie potato. Crucially, starchy potatoes also have a different starch composition.

The starch in waxy potatoes is almost entirely made up of a polysaccharide called amylopectin. Starchy potatoes, on the other hand, have amylopectin but also a smaller sugar called amylose. A good fry absolutely relies on the comparitive abundance of amylose in it’s starch.

Starch Gelatinisation and Amylose Content Explained

The reason we need to pay attention to the starch composition of our future fry has to do with the way starch behaves when heated in the presence of water.

In the plant cells starch exists as microscopic packages called granules. When we heat the potato these granules will absorb water and burst. The liberated starch molecules then thicken the surrounding water. The whole process is called gelatinisation and I’ve written an entire post about it if you want to know more.

The important thing is that the amylose rich starch in starchy potatoes gelatinises at around 58$\degree$C while starch from waxy potatoes doesn’t start gelatinising until 70$\degree$C.

The upshot of this is that when we cook potatoes, starchy varieties will have cells that are almost completely filled with gelatinised starch with no free water. Waxy potatoes will have cells composed of 30-50% starch granules with much more free water.

This is what makes starchy potatoes good for fries. Water is the enemy of a deep frying and the lack of residual free water makes sure our chips aren’t soggy.

Cell Wall Structure and Internal Fluffiness

As we saw above, all plants have cells walls and when we cook a starchy potato the gelatinised starch expands putting pressure on the cell wall. This pressure pushes the cells away from each other. Well separated and dry cells means a fluffy internal structure.

The cell walls of waxy potatoes, with much less gelatinised starch, experience much less pressure when cooked. So, these potatoes retain a lot more structure. This makes waxy potatoes good for salads and other dishes where you want a potato with a bit of structure.

Not good for fries though.

Frying Your Chip

As I said, most restaurants make reasonable fries. In the case of chain restaurants, like McDonald’s, a lot of applied science has been used to solve the question of how best to fry a chip.

So how these restaurants prepare their fries is a good place to start if we want to understand how to make our own chips.

The Two-Stage Frying Process: Gelatinisation and Crispiness

The first technique used in restaurants is to fry the chips twice. Once at low temperature, around 120$\degree$C, and again, after a short rest, at a much higher temperature, around 190$\degree$C.

The first fry cooks the potato, ensuring all the starch has been gelatinised, and also provides some initial crisping of the exterior. Gelatinised starch also starts leaking from the cells and coating the outside of the chip.

Resting after the first fry lets the chip cool, reducing the risk of overcooking the chip in the second fry. It also provides more time for gelatinised starch to leak from the cells and coat the exterior of the chip.

The final fry cooks the gelatinised starch on the surface of the fry, making it crunchy, and allows some Maillard reactions to occur which gives a good fry its golden colour.

Blanching and Pectin Methylesterase (PME) Activation

Crucial to a crispy fry is the integrity of the cell walls that are at the surface of the fry. The cell wall acts as a scaffold for the gelatinised starch that leaks out the cells during the first fry and resting. If you don’t have a scaffold all that crispy starch will just float away during the second fry.

This is part of the reason why almost every fast-food and casual restaurant blanch their chips before frying. Blanching washes away excess starch on the surface of the potato that can burn during frying but, if the blanching water is between 60$\degree$C and 70$\degree$C, it also strengthens the cell walls.

The theory behind this is that potatoes contain an enzyme called pectin methylesterase (PME). This enzyme promotes (scientifically it ‘catalyses’) reactions between molecules of a carbohydrate called pectin in the walls of the cells in the potato. This cross-linking strengthens the cell wall so it doesn’t breakdown during frying.

What the hell is an enzyme?

Enzymes are proteins that catalyse chemical reactions. This is a fancy way of saying that the enzyme forces a chemical reaction to take place faster than it would naturally. Enzymes are everywhere in biological systems, including the human body, and we often use enzymes in cooking, sometimes without even knowing we are using them. Processes like fermentation, bread making, marinading meats and making cheese all use enzymes in one way or another.

All enzymes have a temperature range in which they work. If you are guessing that PME works between 60$\degree$C and 70$\degree$C you’d be right. Blanching the fry in this temperature range gives PME a chance to strengthen the cell wall.

Feature	Starchy Potatoes (e.g., Russet)	Waxy Potatoes (e.g., Cherie, Yukon Gold*)
Starch Type	High Amylose + Amylopectin	Predominantly Amylopectin
Gelatinisation Temp	Lower (~58°C / 136°F)	Higher (~70°C / 158°F)
Free Water Content	Very Low (Bound in starch)	High (Releases upon chewing)
Best Fry Characteristic	Crispy shell, light fluffy interior	Soggy exterior, dense texture

*Note: Yukon Gold is often considered an all-purpose potato, sitting right in the middle of the starchy-to-waxy spectrum.

How Do We Do This At Home?

So that’s how you make fries. Choose the right potato, blanch the fries and then double fry them. Seems easy, right?

The problem for the home cook is that we don’t have things like water bathes to blanch precisely at the right temperatures nor do we have multiple deep fryers for frying at different temperatures.

Frying is even more problematic. Because we don’t have industrial deep fryers we need to batch fry our chips. Each batch of fries lowers the temperature of the oil which means we need to wait to get the oil back up to temperature before the next batch. The result is mostly cold chips.

Most importantly we don’t have time to go through this entire process when we have guests or family to feed. So what can we do?

The Robuchon Method

The chef Joel Robuchon gets the prize for the producing fries with the lowest amount of effort. Simply put some uncooked fries into cold oil in a pot and put the pot on the burner.

After about an hour you have some fries. An hour is still a long time but there is not much effort required and the chips, while not as crunchy as the traditional method are still pretty good fries.

The McGee Method

Harold McGee suggests skipping the rest period and just starting the chips in a low temp oil and after ten minutes turning the temperature up. This also works pretty well though you still need to batch your fries or the temperature of the oil will drop precipitately in the low temperature fry.

I’m also thinking he has some good equipment as my home hob doesn’t have the grunt to get large amounts of oil up to different temperatures that quickly.

Parboiling Your Fries Instead of the First Fry

You could boil your potatoes first then do a high temperature fry, though J. Kenji López-Alt did this and got fries with a crispy layer half as wide as chips cooked using the double fry method.

But Lopez-Alt also found a way of strengthening pectin the the cell walls by using acid, which stabilises pectin, blanching his fries in boiling water spiked with vinegar (roughly one tablespoon per litre) before frying twice as per usual.

A Lazy Scientist’s Shortcut Method for Home Kitchens

The method I use is an interesting study in ignorance bumbling it’s way to some sort of success. My goal was a minimum effort but now I know some the science I can see why this method works reasonably well.

First, I parboil my potatoes, starting them off in lots of cold water. It takes ten minutes or so for the water to start boiling and while it’s getting up to temperature it spends some time in the 60$\degree$C-70$\degree$C sweet spot for PME activity. It’s not as effective as blanching at 65$\degree$C for 15 minutes but it’s something.

Once cooked, I give the potatoes a wash and let them cool in the fridge, giving the potatoes a chance to dry out and get rid of some of the water that is the enemy of good fries.

Next I just dump all my fries into a lot of oil that is at a temperature of at least 180$\degree$C. Because I’m adding so many fries the temperature of the oil drops but I keep the heat on full so the temperature starts climbing again. Then I let the fries cook till they turn golden.

By doing this I’m basically following the McGee method of starting with oil at low temperature and turning up the heat.

The major advantage of this method is you can cook your potatoes well in advance, keep them in the fridge and start frying them when it is convenient to get everything on the table at the same time.

Are they the best fries in the world? Definitely not. Are they good enough that I get the odd ‘nice fries’ compliment? Yes they are.

Conclusion

In this post I’ve barely scratched the surface of potato cookery and french fries. Others have gone much further down the french fry rabbit hole. For example, the International Culinary Center summarises their method for french fries (part one is here) as follows:

Soak the cut fries for one hour in a room temperature solution of Pectinex SP-L (a pectolytic and hemicellulolytic enzyme mix), blanch in boiling water (don’t overload your blanching container) for 14 minutes 30 seconds (assuming your water takes 1:30 to get back to boil), do not dry before frying.

I enjoy their dedication to solving the mysteries of french fries but there is no way I’m doing this on a Saturday afternoon while trying to entertain friends and family.

J. Kenji López-Alt has developed a much more user friendly methodology in detail in his book and his blog (and here as well by Sho Spaeth), and this is well worth reading (and stealing). Harold Mcgee is, as usual, also well worth consulting when developing a method for your own fries.

I’m probably going to stick with my method, because I’m lazy and generally have other things I’m trying to cook apart from fries. But I will be adding some vinegar to my water when parboiling my spuds to see what happens.

In the end I guess it is up to you how far you want to take your quest for homemade french fries. We know how restaurants do it and now that we know some of the science at least we know what we are doing when we try cutting some corners.