some aspects of espresso extraction - 2

an espresso taste test

does this systematic approach to proper extraction levels work for espresso? i tested this idea with an acidic blend roasted so lightly as to be at the limit of current us espresso making practice. i wanted to see if manipulating the extraction could get comfortable, rather than bleeding edge, shots from this blend. i also tested the same extraction levels on the blend roasted to the more usual vienna roast level.

i had previously worked out a way to measure and control the solubles yield in espresso by varying the dose and grind ( see next section ). i was aiming for extractions from 16% to 24% solubles yield. to get this, i used an lm triple basket, and did shots at 12 grams, 14.5 grams, 17 grams, and 19.5 grams, grinding each dose so get normal double shots in around 25 to 35 seconds. i did six shots at each dose level, and measured the extraction level.

four of the shots at each dose were done with the city (northern italian) roast, two at a vienna (southern italian) roast. the coffee was a 50/50 mix of idido, a dp yrgacheffe with floral, citrus, chocolate, and green tea flavors, and cenaproc, a wp bolivian bourbon with an apple acidity and very sweet marzipan caramels. i rated the aroma, mouthfeel, and crema appearance of each shot on a zero to ten scale. i also rated the balance of acidic to bitter flavors, with zero as most acidic, ten most bitter, and five as neutral. finally, ı rated the overall sweetness from zero to ten.

there were two flaws to this test; so these results need to be confirmed.

i. when i came up with the acid/bitter scale, i did not appreciate the nature of light maillard flavors. these are both bitter and fast extracting. i was under the mistaken impression that all bitter flavors extract slowly. this flaw is ameliorated since the blend in this test was mainly fruity, with few light maillard flavors. so under-extraction is signaled by a excessive sourness, not bitterness.

ii. the tasting was not blind; i knew what the predicted yield was when i tasted. since i did not know the actual yield, it is possible to detect and compensate for any bias. my tasting scores followed actual yields more closely than the predicted ones, so i do not believe bias was a major factor.

the crema, mouthfeel and aroma had no relation to the solubles yield ( 3 ). it is possible to get excellent and alas lousy shots in these aspects at all yields

as the extraction model predicts, higher yield shots tended to be sweeter than lower yield ones for all roasts ( 4 ); but lighter roasts responded to yield differences more dramatically than dark ones. this is logical, since dark caramels are not as sweet as light ones. at very high yields, the light roast shots became distinctly caramel flavored, indicating over-extraction. extractions around 23% for the light roast, and around 20% for the dark one tasted the best balanced.

higher yield shots tended to a more bitter balance, and lower yield ones to a more acidic balance⁽⁵⁾. this was equally true for light and dark roasts, although the darker roast was of course more bitter over the entire series. this effect would not have occurred with a light roasted, low acid coffee dominated by light maillard flavors, such as a monsooned malabar. ın such a coffee, the taste would have been bitter at all yields, with increasing sweetness at higher yields.

while this taste test is hardly conclusive, it does support the relationship between solubles yield and taste implicit in ted lingle's work on the flavor chemistry of coffee. it should encourage people who enjoy espresso to experiment with varying the solubles yield in their shots, and to confirm that the shot's taste can be tuned by doing this.

written by jim schulman