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Every roast potato recipe has a list of steps, and most of them come with no explanation. Parboil them. Add baking soda. Shake the pan. Preheat the fat. We wanted to know which steps carry the weight, so we roasted the same potatoes five ways, changing one thing at a time.
How we tested
We used 1 kg (2.2 lb) of Yukon Gold potatoes per batch, all from the same bag, peeled and cut into 5 cm (2 inch) chunks. Each batch got 60 ml (¼ cup) of olive oil and 1 teaspoon of fine salt, and roasted at 220°C (425°F) on the same rack position of the same oven for 50 minutes, turning once at 30 minutes. Two editors tasted blind and scored crispness and interior texture out of 10.
| Batch | Method | Crisp | Interior |
|---|---|---|---|
| A | Raw chunks, tossed in oil | 3 | 6 |
| B | Parboiled 8 min in salted water | 5 | 8 |
| C | Parboiled, then shaken in the pot to rough up | 7 | 8 |
| D | Parboiled with baking soda, shaken | 9 | 8 |
| E | Same as D, tipped into preheated oil | 9.5 | 9 |
What each step does
Parboiling (A to B). Raw potatoes roast from the outside in, so the surface dries and browns before the center is soft. Parboiling cooks the inside first and gelatinizes the starch on the surface. That starchy layer is what crisps.
Roughing up (B to C). Shaking the drained potatoes in the pot breaks up the surface into a fuzzy, starchy paste. More rough surface means more edges, and edges are where the browning happens. This was the biggest single jump in our test.
Baking soda (C to D). Half a teaspoon of baking soda in 2 litres of water raises the pH. Alkaline water breaks down pectin, the glue between potato cells, faster. The outer layer turns softer and slurries more when you shake it, which gives an even thicker crust. Batch D had a glassy, crackly shell the others lacked.
Preheated fat (D to E). Potatoes going into hot oil start frying on contact instead of sitting in cool oil while it heats up. The difference was smaller than we expected, but the bottoms of batch E were noticeably more even and less likely to stick.
The recipe we landed on
Serves 4. Active time: 15 minutes. Total time: 1 hour 10 minutes.
- 1.2 kg (2.6 lb) Yukon Gold or other medium-starch potatoes
- 2 litres (8½ cups) water
- 1 tablespoon fine salt, plus more to finish
- ½ teaspoon baking soda
- 75 ml (5 tablespoons) olive oil, beef dripping or duck fat
- 4 garlic cloves, smashed, and a few rosemary sprigs (optional)
- Heat the oven to 220°C (425°F) with a large sheet pan on the middle rack, oil already in it.
- Peel the potatoes and cut into 5 cm (2 inch) chunks.
- Bring the water, salt and baking soda to a boil. Add the potatoes and boil for 8 to 10 minutes, until a knife slides into the edges but meets resistance at the center.
- Drain well and let steam in the colander for 2 minutes. Tip back into the pot, lid on, and shake hard 4 or 5 times until the edges look fluffy and coated in paste.
- Carefully pull out the hot pan and tip in the potatoes. Turn them in the oil with a spatula and spread them out with space between each piece.
- Roast for 30 minutes. Turn each piece, add the garlic and rosemary, and roast another 20 to 25 minutes, until deep golden.
- Season with flaky salt and serve straight away.
Choosing the potato
Waxy potatoes such as new potatoes hold their shape but never get fluffy inside or craggy outside. Very starchy russets give the most dramatic crust but can fall apart in the parboil, so cut them larger and boil for a minute or two less. Yukon Golds sit in the middle and forgive small timing errors, which is why they won our test.