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Permalink Reply by Edmond Keung on April 30, 2010 at 9:37am

hi J. John

Thank you very much on your reply. Those are very solids methodology and experiment procedures to follow. I now work for a small cafe and I am sure this methodology can definitely help the cafe in narrow down the range and variable when pulling espresso. Thank you very much!.

Edmond

Dr. Joseph John said:

There is a logical way to determine how much espresso you should accept. The technique is called fractionation.

Suppose you wish to determine when to stop a double shot.

Assemble about eight shot glasses. Dose and tamp a double basket of ground coffee in a portafilter with only one spout. Use the manual button to start the extraction. Using the first shot glass, collect about half ounce of espresso. Quickly move that out of the way and collect the next half ounce in the second shot glass. Move that out of the way and collect the next half ounce in the third shot glass; and so on till all eight shot glasses have been used.

Now taste them, one by one, starting with the first and ending with the eighth. You will probably find that by the time you get to the fourth or fifth, all you are tasting is brown warm water, no coffee flavors.

Repeat the whole process, this time collecting may be a quarter ounce in each shot glass. If you taste them now, perhaps you find that by the time you get to the seventh glass all coffee flavor is gone.

This process will give you a quantitative way to determine when you have extracted enough out of the ground coffee, using your blend, ground and packed the way you draw espresso, and based on how your machine is configured.

What you done so far is a "differential experiment." In the second experiment above, if you taste the fifth glass, you are determining what you get in the fifth quarter ounce after you have already extracted a full ounce in the first four glasses. But that is not how you consume espresso.

For that you have to follow with an "integral" measurement. You repeat the same fractionation in quarter ounces as in the last measurement, but instead of tasting each glass by itself, you taste the first, sipping as little as possible. That is what the espresso would taste if you stopped the extraction at a quarter ounce.

Now combine the first two glasses and taste. That is approximately what the espresso would taste if you stopped at half ounce. Now add the content of the third glass and it would be the taste of espresso if you stopped at three quarter ounce. An so on, till you find adding the contents of another glass really dilutes it.

This set of measurements will give you a somewhat rational means of determining the volume to extract.

There are errors introduced:

1. By transferring espresso from one glass to another and thereby losing much of the crema.

2. By sipping too much espresso in the tasting process.

But it is definitely better than guessing.

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