Lightening of the shot

[maurice]

This is one for the coffee chemists amongst us!

Do we know what is actually taking place when the stream of espresso begins to lighten?

Some changes in the composition of the liquid/suspension must be occurring. But what changes? And why is the change in colour so closely linked to a change in the taste?

[Joey]

I guess first come the strongest flavors, specially with the oils (the darker brown stains, sometimes tigerstripes come from the oils) then follows the "rest". The soaked grounds release the flavor and maybe some "color", too. So when water rinsed the grounds for some while there can't be as much content left as at the beginning - so it gets lighter in color and taste: Try to catch the first half of the shot in one glass and the second half in another - then taste the difference.
Hope I am right, that just seems reasonable to me...I am curious if anyone knows the real reason...our roasters should!

[michel]

I've heard and read that there are a lot of barista's in Italy, who put the glass under the stream of coffee a few drops after it begins. Thus, they spill the first drops on purpose..!
As your on in Joey... any ideas?

thanks as always
Michel

[Joey]

Nope. Even if I have to use a shot glass in case of a tall latte in a mug - and I pour the shot into the mug, I even use some drops of the milk to rinse the rest of the crema out of the shot glass. As my coffee is perfect (for me), and I let some water run through the group before "SHOOTING" AND EVEN MY pf HAS THE RIGHT TEMPERATURE ACCORDING TO INTERNATIONAL STANDARDS - WHY; WHY SHOULD i SPILL ONE DROP?? - sorry caps was locked!!!
too lazy to repeat - anyway - I have not found a good reason to do so. But maybe the Italians have one

joey

[kingseven]

I've tried tasting several different sections of espresso taken from when they pour. What amazed me is how awful a lot of them taste until they are balanced by others. A lot of changes are going on as the pour changes colour. The pressure in the brew handle allows the emulsification of the oils in coffee (thus alllowing a crema to be created - the single factor that sets espresso apart from other brew methods - as oils are essential in the creation of foams and colloids *yawn* - I know!)

There is a very neat graph in one of Dr. Illy's articles written for scientific american (I don't have the link to hand but if you google "illy complexity coffee" you should find a load of links) that shows how the concentration of different flavour chemicals change with extraction time - explaining why over extracted coffee tastes rather like a rancid ash tray. If you haven't done it do run another 50ml of water through your puck after you've brewed a couple of shots (talking your 14-15g of coffee here) into a seperate cup and give it a sniff. Its horrid.

I am still not entirely confident of an explanation of why coffee outgasses during the extraction - CO2 being the gas allegedly inside the bubbles.

Apologies for the incoherence here (a little tipsy - its a bank holiday after all....!)

[Joey]

I am still not entirely confident of an explanation of why coffee outgasses during the extraction - CO2 being the gas allegedly inside the bubbles.

CO2 is the gas that comes out of the beans while "degassing", right? Maybe the CO2 coming out during the extraction is just the trapped rest of it - as the beans turn to a wood-like substance during roasting and it might be hard for the gas to dissappear 100%....
Or is this too simple?
joey

[kingseven]

I think its probably more to do with the CO2 having been pressurized during the extraction and now suddenly returning to normal atmospheric pressure. I think outgassing was the wrong word to use - more roast speak than brew speak. I am reading Illy's Coffee Chemistry book at the moment so hopefully he will enlighten me....

[EricC]

I am reading Illy's Coffee Chemistry book at the moment so hopefully he will enlighten me....

Is this the old book or the new book ?

Either way where did you manage to pick it up, and is there another copy to be had ?

Eric.

[maurice]

thanks everyone. I still find it puzzling that the change in colour corresponds so precisely to a worsening of the taste. Does everyone cut their shot off the moment the first light drop appears on the surface of their cup?

I know how bad it tastes/smells if you run a second shot through a used puck. But given what kingseven says - that most sections of the espresso taste awful on their own - how significant is it that the first few drops of light coloured flow taste bad if tried on their own?

[mattmills]

In the Chemistry of Quality this is explained, however i have forgotten the actuall chemical explanation.

What you are seeing is the remaing acids and suggars within the bean. If you imagine that in each grind about 80% is good acids and the about 10 is bad, with the remaining being water etc. The lighter extractiong corisponds to the bad acids

[kingseven]

The version I have I've pinched off someone (he got it in Trieste - they were giving them away I think). Its quite an odd read because you kind of feel you know it already, just not in scientific terms. Well - not all of it obviously.

What I'm curious about is at what point the polysaccarides are extracted - cos they are the surfactant (for those with an interest in foam terminology) and they increase the lifespan of the crema. The quantity of them is obviously affected by the roast degree. Blimey, this roasting business is really quite ridiculously technical. I fear it.