Thirdly, beans are generally roasted in what is referred to as "butter oil", which may or may not be actual clarified butter oil. Occasionally vegetable oils are used, and historically, traditional "home-grown" coffee roasting style involves creating almost a caramel-like coating effect with the use of a small amount of sugar, oil, and generally a touch of vanilla or cocoa. This coating blackens in the roast and the beans wind up with almost a thin, hard shell. Why is this done? Robusta beans are uniquely slow to ripen on the bush, and often pickers pick unripe beans along with ripe beans. The traditional coating gives all the beans a similar color. The presence of a few unripe beans does not hurt the overall taste effect of the blend. However, modern growers pick only ripe beans despite the extra labor, and do not feature this coating in their roasting, opting simple for a little oil to keep the beans easy to turn in the slow roasting process.
Eu também pesquisei técnicas de torrefação no Google. Aparentemente, você deve conseguir um tempo de assadura de 15 a 20 minutos. Então você está gastando vários minutos a 200C. Com uma quantidade tão pequena de manteiga e açúcar, eu me pergunto quando você adiciona os ingredientes extras na panela para não queimar o revestimento.
Se apenas usar o óleo para ajudar os grãos a girar, imagino que adicionar o óleo desde o início funcionará.
Eu poderia ter que tentar isso sozinho.