A blend of the same beans but different roast levels. HDR (high dynamic range) is used in photography to get a better picture combining different apertures. In roasting, it is possible to combine different roast levels to get a more dynamic roast. For example, combining 50% dark roast with 50% light roast we can get a more complex flavor. The darker roast would get for example more body while the lighter roast would add more terroir.

Last weekend I tried doing that with Yemen beans with a friend and that was the first time I heard about this method. He heard about this in Sweetmarias'. I guess like many other things, it will work better with certain beans only.

What do you thing?

With coffee usually referred to as "melange" SO.

Suppose two different flavors are at their peak at two different roast levels. If the flavors are at better than 50% of peak at some intermediate roast level, you are better choosing 100% of that than 50/50 of the two different roast levels. On the other hand, if the flavors you want are not at over 50% at the intermediate roasts, you are better off going melange.

It follows that a melange roast is mostly about combining a very light roast with a very dark one, since a middle roast will usually work better than a combo of two slightly different ones.

Finally, you can get greater roast range in a single roast by running it fast and hot, so that the bean surface is dark and the interior light.

In scientific experiments we want to maximize the dynamic range of our instruments so that data at the extreme ends of the sensitivity of the instrument are not saturated (high end) or noisy (low end). This allows collection of data in one run without the need to either lose and filter out what would be valid measurements or the need to recalibrate the instrument (for example change PMT setting) and remeasure. In this situation all accurately measured data is wanted and useful.

In coffee the melange of roasts could be a good thing if the light roast flavors are favorable to that coffee and equally if the darkest roast you make has favorable extraction profiles. If the middle ground is where that coffee shines then your high dynamic range blend will fall way short on optimal taste. One would I guess need to really know on a bean by bean basis what you want to bring out and emphasize in the cup. My totally uneducated guess is that beans that generally are used in a light roast will work with higher dynamic range roasts or melanges (Africans - Ethiopia or Kenyan) whereas beans that generally prefer darker roasts will not do as well when a significant fraction of the roast is light (Sumatra).