The major acid in green beans is chlorogenic. During the roast that acid is broken down into other organic acids. The longer (and/or darker) the roast, the more all the acids are broken down.
If you want to reduce the acidity without going into darker roast, you can use a slightly lower heat and longer roast.
I start out any new coffee just to the very first hints of second crack, shooting for about a 13 to 15 minute roast time, and adjust from there when necessary.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko