Walking into a kitchen or production location where nuts are being roasted tends to be a delight. The air is full of nutty, caramelly aroma’s. Taking it one step further and burning those nuts deftly removes all that pleasantness and transforms the nuts in black ashy bitter substances that are almost impossible to save. Roasting nuts is a balancing act, getting as much flavour out of them, without over-doing it and ruining them as a result.
Lots of recipes and instructions call for roasting nuts. And whereas it’s tempting to do, because of the clear flavour and smell development, it might not always be actual helpful or useful to roast your nuts. Roasted nuts snack a lot better than unroasted ones, but should you also roast them when you use them on top of your carrot cake? And did you even know you don’t have to use an oven to roast nuts?
Deciding whether to roast your nuts
As we discuss elsewhere on this website, roasting is a great chemical reaction process. During roasting a ton of flavours are formed due to the Maillard reaction. Also, roasting dries out the nut, making it crunchy and it temporarily softens the nuts (making them easier to chop while warm).
So the advantages are clear if you’re trying to chop your nuts, or if you plan on eating them as such (e.g. in a salad). That extra flavour & crunch will be great. However, once your nuts have been roasted they are less resistant to more heat, making them more prone to burning for instance. If your nuts will be heated again, you might not want to pre-roast your nuts!
If in doubt, think through the following considerations:
- Will the walnuts receive quite some heat treatment during the rest of the recipe? If so, do not roast them in advance. An example would be a walnut bread or a pumpkin bread. The walnuts tend to sit on the outside and roast during baking. If they are pre-roasted, they might actually burn. If your nuts do not sit on the outside at all, but stay within a cake for instance, roasting will be helpful (see next point). It won’t get hot enough within the cake for them to burn.
- Does the rest of the recipe contain a lot of moisture in which the walnuts will sit during a heat treatment? Roast the walnuts in advance. The high moisture content will greatly slow down the Maillard reaction so the walnuts won’t brown that much.
- Won’t there be any further heat treatment? Roast the walnuts in advance for optimal flavour.
How to roast nuts
If you do decide to roast your nuts, it’s time to choose how to roast them (assuming you’ve either bought them deshelled or have deshelled them yourselves). The crux to roasting nuts is to heat them warmer than 100°C for some extended period of time. You can do this in various ways, and no, you don’t have to turn on that large oven if all you do is roast a handful of nuts!
1. Air roasting – An oven
Method one is to use hot air to roast your walnuts, using an oven for instance. Air isn’t the most efficient transporter of heat (as we discussed here). As a result, this method takes some patience. The nuts need to be in the hot air for at least 20 minutes before something really changes.
Something else to keep in mind is that in the oven you’d roast your nuts on a rack. The heat transfer from the rack to your nuts will be more eficient than through the air surrounding the nuts. As a result they brown (and burn) more quickly on the bottom, hence the instruction to shake up your nuts sometime halfway. The type of tray you use will influence how well heat gets transferred, darker sheets for instance causes browning more quickly.
Using the oven for roasting walnuts has one great advantage: you can control the temperature easily an you have enough time to decide whether you want them browner or not. If you want them browner, just leave them in longer.
2. Pan roasting – Frying pan
My preferred method is to bake them, without oil, in a frying pan. It’s a lot quicker than using an oven (especially if you plan on having lunch in 5 minutes from now and don’t have time to pre-heat an oven). The heat all comes from the bottom, so you’ll need to shake the pan a little more often. However, because the nuts are in direct contact with the hot surface (which is quite above a hot stove), it all goes very quickly.
The great disadvantage is that it’s pretty easy to burn the walnuts. But that can be solved by being patient (don’t turn the heat to max) and staying around the pan. Also, it’s best to use a thinner pan (not cast iron). Cast iron takes a lot time to heat up. By the time you’re pan is finally hot, your nuts are almost down. A thinner pan works better.
Pre-heat the pan on a medium-high heat. Do not add any oil or the like, just add the walnuts. Shake them regularly and turn them around to assure even heating. They should be done within 5 minutes.
3. Oil roasting – Deep-fryer
Next up is to fry your nuts in hot oil. Oil is a really good heat transporter so heats up your nuts a lot faster than the oven. Since the oil sits all around the nut, it will also give the most evenly browned/roasted nut.
Generally, this method isn’t used for roasting walnuts. Walnuts are almost always roasted using one of the other methods. This probably has to be with the types of fat present in walnuts which make it susceptible to oxidation.
4. The microwave
Yes, it is possible to roast walnuts using a microwave! Even we were skeptic, but having tried it with a few nuts, you can definitely develop some of that roasted flavour. Your nuts won’t turn as dark though since it simply won’t get as hot in the microwave.
However, you have to be a little careful. Microwaves heat your food by heating up the water molecules within your food. If there isn’t that much water (as is the case for a lot of nuts) it might overheat or burn quite easily. Therefore, start by heating you nuts at 20s boosts in the microwave and listen carefully. If you notice they get too hot (or start making too much noise in the microwave) take them out and leave them to cool again.