Sure, but you're making the assumption that your beans are shiny because of butter, while we know all dark-roasted beans will be similarly shiny regardless. You

Sure, but you're making the assumption that your beans are shiny because of butter, while we know all dark-roasted beans will be similarly shiny regardless. You're not providing any clear evidence that butter-roasted beans retain any oils from butter, and frankly I'm very skeptical of that being the case. Have you ever tried heating butter to 300C in a pan? (Do not actually try this, you will start an oil fire and create lots of smoke)