Recap
The extracted mass can be segregated into thirds: bitter, sour, and sweet.
Fermentation plays a large part in the production of the sour/acidic elements in green coffee.
We can calculate the extracted mass with dehydration ovens or refractometers.
The coffee industry uses refractometers because they’re cheaper and they give instant readings.
Extraction yield measurements are averages — we calculate them to see how the measurements change in response to our roasting and brewing decisions, e.g. changes in grind or temperature.
The extremely complex chemical makeup of coffee creates complexities in refractometry that can be resolved with temperature correction calibrations.
This process involves taking a highly accurate dehydration sample and then comparing this sample to RI readings taken at a range of temperatures. This process makes the coffee refractometer accurate to within +- 0.02%TDS.
We emphasise the importance of pairing your sensory skills with refractometry.
New Terms
Acidity: the level of perceived sourness and/or fruitiness.
Agronomist: an expert in the scientific study of soil and plant management.
Aliphatic Acids: the acids of non-aromatic hydrocarbons. In coffee, they are created through the break down of sucrose, fructose and glucose. Of these, the principal in coffee is acetic acid (vinegar).
Caramelisation: a type of non-enzymatic browning of sugar that is brought about by thermal decomposition.
Degradation
Disaccharides: aka a double sugar, are a class of sugars formed when two monosaccharides are bonded by glycosidic linkage (a type of covalent bond specific to carbohydrates) Sucrose is a disaccharide.
Dispersion (optics): when different colours of light refract at different angles — think ‘Dark Side of The Moon’ album cover.
Fermentation: the chemical breakdown of a substance caused by the enzymatic action of yeasts, bacteria and microorganisms.