I've read that almonds roasted slowly at lower temperatures are healthier, which seems to make sense to me.

I found a couple of recipes suggesting 8hrs at 75 deg C or 4hrs at 95 deg C.

With that info, I roasted some at 90 deg C and checked them every hour or so. After 5hrs they were good and crunchy but still didn't have that strong roasted flavour that I was hoping for.

Does the roasted flavour (that I didn't get) come from the Maillard reaction and thus require a temperature over 150 deg C?

If not, what temperature do I need to get that flavour?

  • Are you planning to roast them with salt, sugar, honey or something? – bonCodigo Nov 12 '12 at 21:28
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    @bonCodigo I want to make them into almond butter initially, but if the result is worthwhile I may roast them as a snack too. One recipe I'm keen to try for that uses garlic, rosemary, olive oil and salt. – Highly Irregular Nov 13 '12 at 1:10
  • Wow, savory is definitely on the menu ;) Let me get back to you. There's an awesome outdoor manner for roasting. I could find the inhouse-version for you. – bonCodigo Nov 13 '12 at 1:22

I found these slides that may help. The information is a difficult to interpret, but the page with conclusions says that the optimal roast uses the lowest possible temperature for 20 to 30 minutes. This however is information for the food industry and it is clearly geared towards increasing shelf-life which you are probably not too concerned about.

If you look for the slide with the title 'Generation of flavor compounds during roasting', you will get another perspective. As I understand the graph, a roast at 200ºC (400ºF) for around 25 minutes gives maximum flavour.

This article, although about roasting walnuts, gives clearer information. It states that walnuts are typically roasted at 100-180ºC (212-356ºF) from 5 to 60 minutes. You could infer from this that roasting at 100ºC for an hour is as low and slow as you can go. The conclusion to this article is that the "best sensory properties" are exhibited after roasting at temperatures between 130-150ºC (266-300ºF) for 15 to 20 minutes.

I think that gives you at least four worthwhile experiments to try:

  • 120ºC for 25 minutes (recommendation from the slides)
  • 200ºC for 25 minutes (the time/temperature profile that appears to give maximum flavour)
  • 100ºC for 60 minutes (the apparent limit of low/slow roasting walnuts)
  • 140ºC for 17 minutes (the recommendation for roasting walnuts)

Update: I remembered a fact about the Maillard reaction that could point in another direction of experimentation. Although the reaction needs relatively high heat to get going, once browning has started, the reaction will continue at lower temperatures (as low as 60ºC is what I remember reading). So perhaps you could kick start the reaction by initially roasting at 150ºC (300ºF) or above and then dropping the temperature right down to around 75ºC (170ºF) as soon as browning starts.

  • Thanks Chris! Some great information there! I will update my question with the results at a later date. – Highly Irregular Nov 18 '12 at 2:21

I imagine the argument for almonds roasted at lower temperatures relates to the notion that roasting at higher temperatures would change the chemical structure of the oils and others in the nut. This is a pretty common notion like with cold pressed oils vs. oils that have been heated through its processing. http://www.wisegeek.com/what-is-cold-pressed-oil.htm

However, as you've said, if you just heat it at a low temperature, you're not getting the yummy toastiness that you enjoy.

I would posit that the best way to get the toastiness without impacting ALL the nut would be to toss them on a hot pan (smoke point for almond oil is ~220c) as quickly as possible to til you juuuust smell the toastiness as to not impact the beneficial oils on the inside. I don't know if this would quite work but it's worth a shot :)

After toasting, then you can toss the nuts with your seasoning as to not burn the garlic/rosemary. I'm not even sure if you need olive oil for an adhesive...

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