Why Can't I Get a Good City Roast?

[LT630]

Greetings! This is my first post here. I am a home coffee roaster and have a conundrum that has stumped me. I have been roasting in a hot air popcorn popper, with good results. Ordinarily, I roast my beans Full City to Full City+, right to the verge or right past second crack. I grind the beans with a hand crank conical burr grinder, and brew in a french press. I use 30g of beans for 450g of water, and I brew for 4 minutes in 195 F water. Generally, this gets me a very nice end product.

However, I have recently been experimenting with lighter roasts, in order to try to discern more of the origin characteristics of my beans, and I have not been having the same positive results. When I roast to a City or City+ roast, just past first crack, the resulting brewed coffee is very weak. It is noticeably clearer when I pour it, more like tea than a nice dark coffee color. I even notice a difference in straining out the grounds in my french press. The plunger pushes down with almost no resistance, whereas with my normal roast, it takes a fair amount of pressure.

So, I am at a loss. All the variables are exactly the same in the two situations except the roast level, which shouldn't effect the level of extraction. Should it? I initially thought the problem might be something to do with the amount of water in the beans, with a lighter roast being heavier, which would then result in less beans by volume, which might mean I was using less grounds for the same amount of water. So, I've tired reducing the amount of water I use and measuring by volume instead. I used 350g of water to 30g of beans, or around 12oz of water and 4 tbs of grounds. My coffee was still too weak, again, with all other variables the same. I've not played around much with using different grind sizes for different roasts, perhaps this would make some difference, but I don't really understand why a lighter roast would need a different grind.

Does anyone have any thoughts or suggestions?

Many thanks,
LT630

 

[JohnD18]

LT,
I do not know anything about roasting on a hot air popcorn popper, or the degree of control you have over heat/energy adjustment on it, however I would suggest trying to develop these beans a bit more in the "City" roast degree you're looking for. So, if you have the ability to control the heat, then when you're approaching the degree at which you're aiming for, slow down the ROR, or rate of rise (how fast the bean is gaining energy), and let it develop in this roast degree for a bit longer. You should be able to achieve a fuller body while getting rid of any grassy/sour flavors left in the bean. I am picturing perhaps you could turn off the heat but still have the popper running to some extent, letting the beans sit (spin?) in the popper at a lower temp and drag out the time it is exposed to the desired drop temps.

Again, I know nothing about air or popcorn poppers, so its only a suggestion. Give it a try if possible and let us know if it helped.

 

[Mr.Peaberry]

LT,
IMO, you gave the clue. The clarity of the lighter roast brew suggests that you are not getting the same level of "fines" in your grounds as you get with the near French to French roast. Therefore you are not getting the same level of extraction from the lighter brew. I think you could do a finer grind with the lighter roast to get to where you want to be, and then adjust contact time to suit. You may want to go back to the darker roast except for cupping purposes. Give us an update please!