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Crema by James Hoffmann
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Jules_Gobeil
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Joined: 22 Sep 2006
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Location: Quebec, QC, Canada
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Posted Sun Oct 15, 2006, 1:16pm
Subject: Re: Crema by James Hoffmann
 

kingseven Said:

JulesG - What kind of coffee are you using?  Is it a very dark roast? Any idea how hot your machine is running?.

Posted October 15, 2006 link

I it is a home roast blend based on Brazil beans - roasted to City, City +.  I temp. surf my Silvia and I brew when the heating lamp comes off - at that time, the water temp. in a styrofoam cup under the brew-head is 91-92 C. (196-198 F.).  My thermometer seems quite accurate - it shows 97 C. (207 F.) in boiling water, which is probably right on since it is not completely immersed.

 
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wallisj
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Posted Tue Oct 17, 2006, 9:16am
Subject: Re: Crema by James Hoffmann
 

Excellent opener James....look forward to many more!
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twomartinis
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twomartinis
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Posted Wed Oct 18, 2006, 9:14pm
Subject: Re: Crema by James Hoffmann
 

I definitely connected with the point of crema bubbles acting like tiny packages ready to unleash the aromatics as they burst on your tongue. To me, CO2 is acting as a sublime transporter of flavor; and the surface area aspect is proof of that. It occurs in cupping too, especially at the break, when you unleash that waves of aroma and flavors that are trapped in those tiny suspended bits of goodness. I'm also one of those guys that gets off on smelling the back of the spoon after you are finished adulterating the crust - that increasing surface area thing again...

As to the grinding aspect relating to the range of grinds, I think this is inevitable for now and always. No matter how razor sharp any particular grinder's burrs are there is going to be fracturing as well as cutting action present in the grinding, which will create uncontrolled particle sizes smaller than the intended grind size, not to mention the continued mechanical/friction of the grinds as they are dosed, distributed and packed.

Great article James, spot on.

 
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ThatCoffeeGuy
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Posted Wed Oct 18, 2006, 9:28pm
Subject: Re: Crema by James Hoffmann
 

As I was first reading this article I thought to myself, "Man, this is getting a little too scientific/technical."  But then, as I kept going, I not only enjoyed the more technical parts, but realized how necessary they really were to fully undestanding what was going on.  Then I read your article again, after breaking apart parts that took re-reading the first time through and I feel that I have taken away from the article a whole new knowledge of espresso, that I hadn't really ever thought about deeply before.

A question (and this goes for anyone willing to chime in, not just James):  What does brewing at over 9 bar do to a shot of espresso.  On our readout on our machine I often notice that the needle indicating brew pressure is around 10-11 bars.  Is this anything to be concerned about, and if so why?  What is it doing to the shot?

Anyway... Thanks for a great article and I can't wait for more articles to come!

-Bry

 
Bryan Wray

"I just hope that people realize that coffee is not just a caffeine delivery service, it can be a culinary art." -Christopher Owens
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rmongiovi
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Posted Thu Oct 19, 2006, 2:39pm
Subject: Re: Crema by James Hoffmann
 

A scientific approach to espresso.  That's too appropriate to even comment on.  I've got to take one exception, though.

I've got to agree with David Schomer about the polyphasic nature of crema as described in this article.  "water", "oil", and "foam", aren't phases.  There are three phases of matter (four, if you count plasma, but if you've got plasma in your espresso your temperature and pressure are WAY too high): solid, liquid, and gas.  So you're correct that crema has three phases - the solid bits of coffee that make up your speckles, the liquid making up the bubble wall, and the gas contained inside the bubble.  If that gas actually is the outgassed CO2 from the beans, then losing it should alter the flavor slightly just as soda changes flavor when it goes flat.

Gotta agree it's not a colloid, though.  You need an emulsifier, or a much much finer grinder, to achieve that.
Roy
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Jon_B
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Posted Mon Oct 23, 2006, 12:09pm
Subject: Re: Crema by James Hoffmann
 

As an engineer who's had my share of chemistry and physics classes, I thought your technical descriptions were very well done.

I'm an espresso novice, but as a soils engineer it would seem that the ground beans would act similar to a well-graded sand or gravel. Those fines in the cup could be the "fines that are moved in extraction" that were near the bottom of the puck. Theoretically, the fines should only travel a short distance before they are stopped by a combination of larger particles of varying sizes; however, the fines very near the bottom of the puck may find their way out.

But what do I know? I'm trying to squeeze out a decent shot using a blade grinder and Mr. Coffee espresso simulator.
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dolcimelo
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Posted Tue Oct 24, 2006, 6:01am
Subject: Re: Crema by James Hoffmann
 

rmongiovi Said:

A scientific approach to espresso.  That's too appropriate to even comment on.

Posted October 19, 2006 link

I heartily agree! A bit of evidence to replace opinion, no matter how authoritative, can be no bad thing.

I'd appreciate a clarification, however. In discussing tiger mottling, it was stated that this was an indication of both a good extraction and a good grinder, but, while not denying either, I'm struggling to understand why. If a good grinder produces a good range of particle size, then shouldn't this show up in any extraction? What does a good extraction do that allows the fines present from a good grind to migrate into the cup, but a bad extraction does not do? Why does a really bad grinder not produce this effect, given that the range of sizes would be even more extreme? Or does it? I have also noticed that tiger striping can occur throughout the pour - is this part of the same effect, or something different?

I'd also be interested in the author's views about crema in relation to a recent controversy in the Australasian forums about certain expensive machines not producing Illy-standard foam. Just how important is it going to be for taste (quite apart from definitions of espresso)? Can there be a trade-off, so to speak, between crema and oils?

Gotta agree it's not a colloid, though.  You need an emulsifier, or a much much finer grinder, to achieve that.
Roy

Well, I guess the melanoidin is the emulsifier, but the key is probably the size of the bubbles. It doesn't need to be a stable emulsion to be a colloid, but you'd need bubbles less than about one micrometer; clearly, there're a lot of bubbles a lot bigger than that. If it were an emulsion then, by definition, I guess it would have to be polyphasic. It's certainly a foam... and I like it.

Matt
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kingseven
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Posted Tue Oct 24, 2006, 2:34pm
Subject: Re: Crema by James Hoffmann
 

Ought to clarify when it comes to the phase thing - my description of oil, water and foam as phases comes from the same source I suspect mr Schomer got his quote which is the Illy text.

As for the Aussie thread on machines, I think that got out of context - that those buying certain machines are chasing a goal of taste and sensation in the cup, not huge mounds of foam.  In truth I suspect it will be more about the coffees they select and brew than the equipment.

The range of grind particle sizes - particle size has two important relations, one is resistance to water flow and the other is surface area exposed.  Seeing as water doesn't actually pass through coffee the surface area is vital to your total dissolved solids and the profile of the cup.  A range of particles gives an ideal resistance and available surface area.

Tiger mottling - good vs. bad extraction.  A bad extraction that will not results in tiger mottling is usually one that has channelling.  Here a higher quantity of water runs past the coffee through gaps created by the pressure, failing to force out the smaller particles.  (this is hypothetical!)

An emulsion is a liquid - liquid colloid, such as oil and water.  By definition an emulsion is stable, and also a colloid is defined as such.  The melanoidin is a surfactant but on its own is not sufficient to create a colloid because crema is not stable and dissipates quite quickly.  You could add a stabiliser like xanthan gum and then you would have a colloid.

When I get tiger mottling I see the fines in the start of the pour only  - which makes sense when Jon_B talks about how most of the fines should get trapped once the extraction is up and running.  With my shots it is almost as if the mottling is pulled across the surface of the crema as the shot progresses, from the outside of the cup inwards.

Brew pressure above 9 bars - the published research indicates that higher brew pressures increase bitterness, astringency in the shot, though some positives attributes were noted but I can't remember what they were.  It will ultimately result in overextraction.

Sorry this response is a bit scatty - I need more sleep.

 
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dolcimelo
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Posted Tue Oct 24, 2006, 5:18pm
Subject: Re: Crema by James Hoffmann
 

kingseven Said:

Sorry this response is a bit scatty - I need more sleep.

Posted October 24, 2006 link

Don't be silly, you just need more coffee...

Thanks for the great reply, James. The grind particle size discussion always brings me back to thinking about how this balance works between finer/coarser - more/less - heavier/lighter tamp, etc and flavour, but that's probably off-topic. It is interesting to contemplate what 'finer' or 'coarser' actually means when you have a range of sizes, but I guess, again, it has to do with balance. Then we could look at Turkish coffee, with its own version of crema, too...


An emulsion is a liquid - liquid colloid, such as oil and water.  By definition an emulsion is stable, and also a colloid is defined as such.  The melanoidin is a surfactant but on its own is not sufficient to create a colloid because crema is not stable and dissipates quite quickly.  You could add a stabiliser like xanthan gum and then you would have a colloid.

Emulsions are inherently unstable, hence the need for emusifiers, and your explanation of the draining of liquid got me thinking - when the first espresso is made in microgravity, maybe the crema will last for hours! Which company will have the first espresso machine in space? "Our coffee is out of this world!"
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Pe_tah
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Pe_tah
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Posted Wed Oct 25, 2006, 2:44am
Subject: Re: Crema by James Hoffmann
 

awesome article!

I love food science >=)

 
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