Just grabbing this one. You need only capture when you have the idea. Just write it down on a piece of scrap paper and throw it in your inbox. Or type an email to yourself. Or call your voicemail. Or keep a journal called INBOX and write your ideas there.* How do you capture your new open loops whilst working on an active task. My mind seems to funciton in the way I will think of 5 new items per hour. It feels like I need to break my concentration simply to capture these and make a decision about where to put them.
As you're doing something else, you just write enough to capture the idea along with any details you think you need to fully understand that thought you had.
Processing is a separate step. You may have set times you process or you may process after each completed task but you don't want to stop what you're working on to figure out where to put those 5 ideas you just had. Write them down and keep on working.
Unless of course one of those ideas was "That's the fire alarm; I should get up and go outside." And if it is, take your little notebook with you so you can capture while you're standing outside.