Pre Or Post Blending

Pre or Post Blending Coffee?

This question came up in the Coffeetime forum and I think it's worth making it a small article on the Coffeetime website

When I roast I tend to pre roast blend, and when dealing with commercial roasters I have found most do the same. But the idea of post blending still appeals - you can choose the roast level for each origin to get the best from them - and then combine them in a post blend for a supercharged espresso - anyone got any thoughs or pros/cons?

Well commercial roasters do tend to pre-blend and roast it all together in the drum…..I have seen comments like, they "feel" it "hangs" together better and the roast tastes better etc..

Having been exposed to a bit of commercial roasting, the reason I was given, and this makes much more sense to me, is…with a 25kg batch, it mixes properly in the drum of the roaster and it would be very hard to mix it later. It's purely a convenience thing, although I think roasters trying to convince you of some "magical" techniques, would like you to think otherwise.

Also if you have a 25kg roaster and a blend of 4 beans, you have to roast a minimum of 25kg each batch. Say your blend was

  • 10% Robusta
  • 20% coffee A
  • 30% coffee B
  • 40% Coffee C

To post blend, this would mean roasting 25kg of robusta, of which you would only use 2kg in your blend. Now unless you needed 200kg of espresso blend…..what do you do with the rest of the robusta (same applies for all the other coffees). Oh weights don't add up mathematically cos accounting for up to 20% weight losses on roasting.

All beans don't roast to the same level in the same time….thats it nothing more to it than that. Logically this means that any blend will contain beans roasted to different and possibly sub optimal levels. Any roaster who tells you otherwise, is fooling themselves. Now you could limit yourself to blends that contain beans that all roast to the same level in the same time, or beans that taste good roasted to differing levels. This does however limit what you can have in a blend. So they don't limit themselves and "cup" it to see what tastes best.

However, convenience and practicality is the name of the game.

For the home roaster, or the smaller roaster (and I mean small), post blending makes far more sense. This is because your batch sizes are very small and mixing the beans afterwards is not such a huge problem as with 20 kg batches. You will also not have so much wasteage, but would have to think quite carefully if you wanted to bother with 10% robusta. e.g. in my roaster it would mean having a Kilo of robusta of which I used mabye a few hundered grams….the rest would go stale by the time I next roasted. Solution….I don't use robusta. It also of course means you can't use those busy and impressive sounding 7 bean blends so easily, because you have a LOT of coffee going to waste to create a rather silly 7 bean blend for espresso. e.g. 7kg roasted, to make 1kg of espress blend.

If a commercial roaster tries to creat new blends by post blending, then the flavour of the same blend "must" be very different when pre blended before roasting!.

For the home roaster, in a different way, convenience and practicality is also the name of the game . You decide to roast 3 small batches, some you keep as single varietal beans, some you post blend…..all of course roasted to their optimal level. This means that your blend is likely to taste better, but more difficult to experiment with the more "exotic" blends containing lots of different types of beans.

In addition for the home roaster, if you roast the right 3 or 4 beans, then it's easy to create a few different blends from the same batch, also a great way to experiment with new blends.


  • In both cases it's a practicality issue.
  • Commercial roasters can use/create more exotic blends….but unless beans all roast the same way (and almost certainly they won't), the roasts will be a compromise on potential for flavour.
  • Home and V small roasters (post blending), can use prehaps less types of beans in a blend (for practicality), but can ensure each bean is correctly roasted….maximising potential for flavour.