With the increasing popularity of home roasting, and the wide availability of ever more advanced home-roasting equipment, it is inevitable that some people will experiment with different ways to roast coffee beans, including the idea of re-roasting.
This might happen for example where a novice roaster stops the roasting process a bit too early and finds that the beans seem to be under-roasted.
In another scenario a home roaster may have made a large batch of light or medium roast beans and they want to try to turn some of them into a darker roast.
So, can you re-roast coffee beans? Read on to find out the facts.
Can you Double Roast Coffee Beans?
The short answer is no, it’s not a good idea.
All the experts will tell you that once a coffee bean has been roasted, there is not much more you can do to improve it.
Roasting a second time just cooks the bean, removing any flavour that there might be.
It does seem that this was actually tried commercially in Switzerland a while ago to create low-acid roasts. Beans were roasted to the first crack then left in the roaster to cool down.
When cooled they were then roasted again, supposedly giving a sweeter coffee with less acidity, easier on the stomach.
Whether this was ultimately successful, there is no real evidence, except that this practice was never continued and did not become popular, which probably tells you everything you need to know about that.
Some people claim to have some success with pan roasting coffee beans twice, carefully shaking the beans around the pan as they roast, and watching carefully to see what is happening to the bean.
As an experiment, it might be worth a try, but it seems a lot of trouble to go to for a sub-standard cup of coffee.
It would be better to put much more effort into making sure that the beans were roasted to perfection the first time around.
Can You Buy Double or Triple Roasted Beans?
You may have actually heard about double roasts, or even triple roasts, and possibly you might see them for sale in online stores or specialty coffee shops.
But these are not beans that have been roasted more than once. They are in fact coffees that are blends of different roast profiles.
As you may know, light roasts have flavours that are floral and fruity, and dark roasts tend to have notes of caramel and chocolate.
What they call a double roast is in fact a blend of two roast profiles, with the idea of combining the best flavours of each of the roast types.
A triple roast is a blend of light, medium and dark roasted beans.
This does sound interesting, and if you see them on sale you should try this, it is even certainly something you can try at home with your own roaster machine.
Can I Re-roast Coffee Beans to Make Them Darker?
Re-roasting coffee beans will for sure make them darker, but that will be on the surface only, in a sense burning the outer shell of the bean.
The chemical reactions that produce flavour and aroma have already happened, and roasting the beans a second time will not improve that.
In fact when roasted a second time the beans are cooked to the point where they lose their flavour and are hardly recognisable as coffee at all.
The beauty of a real dark roast in the development of the oils and acids in the bean, bringing the oil to the surface of the bean, producing that strong, bitter taste associated with a dark roast.
Re-roasting light or medium roast beans to try to make them into a dark roast will just burn the beans, giving you small lumps of charcoal.
How to Roast Coffee Beans Already Roasted?
Everything written here says that you should not re-roast coffee beans.
Of course you are welcome to try, sometimes we learn not by listening or reading, but by doing, so we find out for ourselves.
However there is one possible scenario where you can try to re-roast your coffee beans.
This is in a situation where you are roasting some beans at home, and you stop the process because you think the beans have reached the correct stage, giving you your desired roast profile.
You take the beans out of the roasting machine, and then you realise you were wrong and the roast is too light and under-roasted.
If you are quick enough you can put the beans back in the machine before they have a chance to cool down, and re-start the roast.
Of course this has to happen before the First Crack, and I suppose it is more a continuation of the roasting process rather than a re-roast process.
But everything we know about coffee bean roasting tells us this is the only situation where you can in effect roast the same beans twice.
What Happens If I Double Roast Coffee Beans?
You may have heard of the Maillard Reaction. This basically is what happens with many cooked foods including coffee beans that turns them brown and develops their flavour.
Under heat, sugars and proteins react with carbohydrates, elevating the flavour, aroma and colour of the food.
A simple example of the Maillard reaction is toasted bread. Light fluffy bread becomes a darker colour, turns crisp and changes its flavour.
Exactly the same thing happens with coffee beans.
With coffee beans, the Maillard reaction occurs at the same time that the moisture in the bean tries to force its way out, breaking the cell structure of the bean, making a cracking sound, what we call the First Crack.
The Maillard reaction can only happen once, so double roasting the same coffee bean will do nothing to help the flavour develop further, in fact the complete opposite – all the flavour will be cooked out of the bean.
Given that coffee beans are not the most expensive items on the world market, our advice would be that if you have an under-roasted batch of beans, just throw them out and try again with new beans.
Of course you can experiment, and become like a Doctor Frankenstein of coffee, trying to breathe new life into a dead bean 💀
But really you will never make it as good as a fresh single roasted coffee bean.
Life is too short to drink bad coffee!