Hi guys,

What's the science behind oil formation, and why does it flow out from the bean with (1) high-heat roasting and (2) age (for City + - FC roasts)?

Maybe someone can give a biochemical perspective.

wearashirt wrote:...

What's the science behind oil formation, and why does it flow out from the bean with (1) high-heat roasting and (2) age (for City + - FC roasts)

Dark roasts are taken into 2nd crack in the roasting process. That event destroys the cellular construct of the bean. Coffee contains naturally growing oils. As time passes (or too deeply roasted), those oils migrate to the exterior of the bean past destroyed cell walls.

I have never had city plus demonstrate oils but then, my roasts at C+ are long gone by 10 days.

Boldjava wrote: I have never had city plus demonstrate oils but then, my roasts at C+ are long gone by 10 days.

I regularly see roasts around C+ to FC develop oils if left for long enough, usually 10+ days out.

Boldjava wrote:Dark roasts are taken into 2nd crack in the roasting process. That event destroys the cellular construct of the bean. Coffee contains naturally growing oils. As time passes (or too deeply roasted), those oils migrate to the exterior of the bean past destroyed cell walls.

I have never had city plus demonstrate oils but then, my roasts at C+ are long gone by 10 days.

Thanks Dave. That's a good explanation.

What's your opinion on oils on the surface, by the way?

wearashirt wrote:...What's your opinion on oils on the surface, by the way?

I don't roast that dark. When customers come in for demonstrations, I teach them how to go into second, for two reasons:
* Sound and sight recognition of 2nd crack, and,
* They will have customers who insist on dark roasts.

I don't roast that dark for the shop consumption or myself. I don't care for the roast characteristic/oils to be the dominant presence in the cup. That kind of roasting removes the fine fruits, florals, flavors, and nuances of the high quality greens we seek to offer.

The darkest I ever roast is about 5 pops into second for an espresso roast and then only when that depth is best in any single origin for espresso roast. I usually stop an espresso roast when it is completely through 1st crack and on the cusp of 2nd crack. Each bean has its own best presentation.

Same here, about the only time I take them into the second crack is about the same time I'm saying Oh, Crap! My second cracks come right at 442-444F, I normally never take beans beyond 440-441F. If I keep espresso beans for more than a week, they will sometimes start showing tiny drops of oil on them.

I had this exact question too before. Above responses are right too, but in my opinion that is what happens after the oil is formed internally. I suspect the oil was generated from breaking down of certain components (supposedly the nutrient for the seedling). I'm not sure which component, but it's probably a long molecular chain compound that is solid-like at room temp. The newly 'generated' oil has a lower melting point and thus can migrate. Pseudo science warning though as I have no literature back up to support.

samuellaw178 wrote:I had this exact question too before. Above responses are right too, but in my opinion that is what happens after the oil is formed internally...

Oils are present both in the raw and roasted forms of coffee. The plant physiology and the food chemistry of roasting on this can make my head hurt. Badly.

http://www.aromaweb.com/essential-oils/coffee-oil.asp
http://www.scielo.br/scielo.php?pid=S16 ... ci_arttext

Thank you Dave!