What happens with very light roasts made through espresso?
I've been playing around with putting my filter roasts through the espresso machine, and I've noticed it's very difficult to get a shot out properly.
When extracting a normal espresso roast (once I've dialed in the grind), the drips? come through in a few streams and come together quickly into a thick syrupy stream.
When I try to do the same process with a light roast, I notice the drips are very thin before and after coming together. I do adjust the grind accordingly, but find the window for a correct grind to be much smaller than with a darker roast - e.g.: a notch on the Mazzer may be too much adjustment for the light roast, whereas for the darker roast it's a step in the right direction.
What are the chemical properties in a light roast that may cause this? I also note the lighter roasts are more prone to channeling and the occasional spray, even though the distribution/leveling and tamping technique is exactly the same.
Originally Posted by davidxcoffee
... Where to start?
As generalisations, there may be a few exceptions. There is no substitute for doing your own testing / checking / verifying using your own gear (including roaster, grinder and machine as a starter - trees / farm etc if you are more lucky).
1) Darker roasts are more soluble than lighter roasts. This has 4 main flow on effects:-
a) you can get away with a worse grinder (the "logs" dissolve faster relative to the "unwanted fines" so particle spread is less important). In my view, explains a lot of the sillier posts in CS about crappy grinders.
b) the shot starts to appear and then go through faster (ALL other things being equal).
c) They are more susceptible to aging. This is where the traditional "roasts are best from 4 to 11 days" maxim comes from. I use a simple test - if it smells green, it is! Really light roasts may take weeks before they are ready to use. BTW, this is probably where most of the derided "wheatgrass" comments about 3rd wave coffees in CS probably originate. Using pourover / plunger et. al. allows you to get away with a lot more green in the cup.
d) If you are a crema volume fan, buy fresh Robusta or roast Arabica dark. By the time a really light roast comes on stream (i.e. ready to use) it will be older so the crema will always be less in quantity - mind you, it can be a lot better in quality...
Back to your shot question - mainly 1 b) - more comes through faster and appears thicker. If your final extraction ratio is also higher, it will have a slightly higher density as well.
I was going to continue (no 2, 3, 4 etc), however that should be enough to amuse you for a while.
Enjoy your current cuppa - all else is secondary.