What Causes Bitterness in Beginner's Roasts?

[NobHillNotary]

Hi everyone: I've been noting the organic Columbian beans I have are beginning to taste a little bitter as city roast medium. I use the same filter I always have on my AeroPress, the paper. I have made sure to get chaff out of the coffee using a strong hair dryer. I don't understand how this can happen. The beans I bought only recently within the past month. The beans were roasted under 10 minutes in a Whirley Popper. When I first began this process I didn't note a bitter taste.

Can someone please help me? There's nothing worse then bitterness in coffee. Thank you.

 

[lbeery]

Maybe you need to go a little longer?

 

[SandraH]

How much are you roasting? 10 minutes should be a good time frame.