The secret to extra-crispy roast potatoes, according to a food writer

Roast potatoes that stay soft on the outside are a familiar disappointment: the oven was hot, the oil was there, and still no proper crust.

So when food writer J. Kenji López-Alt set out to perfect the classic roast potato, he tested almost everything that could affect the result: from the type and size of the potatoes to how they were boiled and roasted.

One of his smallest changes turned out to be one of the most interesting.

It involves something you probably already have in the kitchen, but probably wouldn't think to add to a saucepan of potatoes.

López-Alt's Serious Eats method has since become well known for producing potatoes with a deeply crisp exterior and soft, fluffy centers.

So what is that little extra step, and why does it make such a difference?

It starts before the potatoes reach the oven

The method is surprisingly straightforward.

For about 2 kg of potatoes, López-Alt uses roughly 1.9 litres of water, 2 tablespoons of salt and half a teaspoon of baking soda. Russets are preferred, although Yukon Gold potatoes can also be used. The potatoes are cut into large chunks and simmered for around 10 minutes, until mostly tender.

Then comes the part that can feel completely wrong.

After draining, the potatoes are tossed vigorously with oil or fat until their surfaces become rough and some of the cooked potato breaks down into a starchy coating.

In The Kitchn's test of the recipe, the tester found that this rough exterior was crucial to the final texture. The potatoes looked almost mashed around the edges before they went into the oven.

That's exactly what you want.

Why baking soda helps

Baking soda is alkaline, so adding it to the cooking water makes the water more alkaline than ordinary salted water.

That helps soften the potato's outer layer during boiling, creating a surface that is easier to rough up. More starch ends up exposed on the outside, leaving the potatoes covered in tiny uneven edges.

Once those pieces hit a hot oven, those rough, starchy surfaces have plenty of area to brown and crisp.

The Kitchn's 2026 roast-potato comparison tested López-Alt's method alongside five others and rated it 9.1 out of 10. The tester described the finished potatoes as crunchy outside, with soft and fluffy interiors.

So the baking soda isn't there to season the potatoes. It's helping create the surface that eventually becomes the crust.

Don't grab the wrong box

There's one easy mistake to avoid.

Baking soda and baking powder are not interchangeable.

Baking soda is sodium bicarbonate. Baking powder also contains sodium bicarbonate, but it includes acids and other ingredients designed to help baked goods rise.

For this method, you want baking soda.

And half a teaspoon is enough for roughly 2 kg of potatoes. Adding more isn't a shortcut to better results and can affect the flavour.

Finish with plenty of heat

Once the potatoes have been boiled and roughed up, they need a hot oven.

López-Alt's method uses around 450°F (230°C), with the potatoes turned during roasting so they brown evenly. The Kitchn's testing found that the potatoes needed roughly an hour to develop their crisp exterior, although cooking time can vary depending on the potatoes and oven. 

There is no need to chase the darkest possible crust, either. The UK's Food Standards Agency recommends aiming for a golden-yellow colour or lighter when roasting starchy foods such as potatoes, as darker browning can mean more acrylamide has formed. 

So next time your roast potatoes need a little more crunch, don't immediately reach for more oil or turn the oven higher. All it takes is some boiling water and half a teaspoon of baking soda.