How to convert a bread maker in to a home coffee roaster (Coretto Method)

This is a guide to make a cheap fully functional home roaster out of a bread maker.

The Coretto Method is a very common roast method, many users get exquisite results just as good as high-end equipment roasters can deliver. With some small modifications you can even roast by profile.

The basics of the method, is that the dough arm in the bottom of the bread pan, mixes the beans for an even roast. A heat gun from your local hardware store will deliver the hot air in to the pan, roasting your beans. A bread maker can be bought for less than 80$ same goes for the heat gun. I bought both secondhand, saving more than half the price of new. In a Coretto, you can without any problem roast 500gr batches. Compared to the other option, the popper this is way more convenient.

It can be done in two ways, each with different modifications.

The easy way
Open Coretto

The easiest and most effortless way, is simply to open the lid, and place the heat gun in a stand pointing at the beans. There are some things to be aware of though. You have to look and listen closely, and determine the roast by sight. Most people keeps a fan near the heat gun to prevent chaff from getting to its intake, it won’t survive for long, getting chaff in there all the time. It’s going to take some batches getting the time and heat in order. You will control the heat by switching the levels on the gun up and down. 

The geeky way
Closed Coretto

This way many think you get a sweeter roast. I choose it because i think that you get more control, because the heat loss is significantly smaller.

The closed way can be done in several ways:

The lid:
One option is to simply drill a hole thru the original lid, placing the heat gun in the hole. I wouldn’t recommend that, because of the fire hazard. The temperature gets really high, and the lid is typically a simple plastic shield, with an inner lid of thin aluminum. Make your own lid, if you have the tools and the craftsmanship you can make a lid appropriate to your needs.

 I Did 

 

If you just want it nice and easy, but still closed, use a bathroom tile and a stand for the heat gun, leaving a gap at the side to entry air. This way you can slide the tile back and forth, looking, listening and even controlling small parts of the temperature letting heat out.

Thermocouple (TC)

Mounting a TC thru the side lets you know the bean temperature. It’s essential when roasting by profile, and very useful when starting home roasting because you can see the different stages much easier. There is different TC on the market, combined with software to log your roast on a computer, this way you don’t need to write it all down by hand. It’s a good gadget, very time saving, but also quite expensive in my opinion.    

Insulation
A way to keep even more temperature stability, is to insulate the pan. Easiest way to do this, is to wrap the pan with a fire blanket and steel wire. Often you would have to remove the original heat element from the bread maker, or else there won’t be enough room for the pan. 

Heat control
Control of your roast to the smallest detail requires a mod, controlling the heat element inside the heat gun. To control the heat gun, you need a light dimmer. Most heat guns are 2000W, therefore you need a big light dimmer, and they are really expensive. So if you already know, that you want the option of stepless heat control, consider buying a heat gun with stepless control from the beginning. They are not much more expensive than the other ones, but they are defiantly a lot cheaper than the dimmer. 

Exhaust
If you don’t want the chaff flying around inside the pan, you need to make some kind of exhaust. I made my lid slightly bigger than the machine, this way two corners are open, letting out the chaff this way. Others have made their thru the side or in the lid. 

Of course most of the mods above, can also be made for the open coretto.

Keep safety in mind. The parts used in the coretto were not meant for the purpose.

Always keep a fire extinguisher in range.
Never leave the machines while running, or still hot.
Use your common sense, if its looks like going wrong, abort and start over when cooled down.
Coffee channel can in no way be held responsible for any damage you may have dealt to your equipment or surroundings.

I have just yesterday received three kinds of different raw beans from The Coffee Collective; I’m going to roast them in my coretto, showing the results along with a review on the blog.

Enjoy roasting

Best regards

Caspar