“Solubility matching” and blending coffee — Scott Rao

A few years back there was a trend called “solubility matching,” an attempt to blend coffees of similar solubility. The idea was appealing but never seemed to gain traction or improve the quality of blends. What is solubility? And what is solubility matching? And does it matter?

Solubility is a property referring to the ability for a given substance, a solute, to dissolve in a solvent. Simple enough. It is estimated that just over 30% of a coffee bean’s weight is soluble in hot water. Roast development, coffee variety, and, I believe, coffee density, among other factors, influence the solubility of a particular bean.

Underdeveloped roasts tend to be less soluble than well-developed roasts. Very dark roasting decreases solubility by burning off some of a beans soluble mass. The most soluble roasts seem to be well-developed, light-to-medium roasts.

I have reached extractions as high as 28%—29% (most often with Kenyan and Ethiopian coffees) using extraction methods such as the Blooming Espresso, Vacuum-pot brewing, and the Tricolate brewer, all of which offer opportunities to achieve near-complete extractions. I imagine I’m still a few percentage points away from “complete” extraction, or exhausting a coffee’s solubility, without resorting to hydrolysis, as many instant-coffee manufacturers do.

“Solubility matching” is the appealing idea of blending coffees with similar solubilities. I believe the assumption behind solubility matching was that blending coffees of similar solubilities would improve flavor or extraction level. One difficulty of solubility matching was that it severely limited what coffees one could blend together. Recent efforts to revisit solubility matching have confirmed for me that blending two coffees of different solubility levels merely creates a resulting coffee with an extraction level that is approximately the weighted average of the extraction levels of the two blend components, and a required grind setting that is likewise similar to the component’s weighted-average grind sizes. (Jonathan Gagné recently confirmed for me that blending two coffees creates a blended version of their particle-size distributions.)

As for flavor, I have never found a formula or a shortcut to creating a great blend. Solubility matching hasn’t improved my results. Given that green coffee is always slowly fading and roast batches often vary in quality, I believe informed trial and error, with lots of blind tasting, is still the only practical way to create and manage a great blend.

The only shortcut I use to blend coffee is the well-known “spoon method”: pour a cupping bowl or brew a cup of each blend component you are considering using. Spoon some of each blend component into a separate, clean cup. For instance, if you have three blend components and want to taste a 3:2:1 blend, blend three spoons-full from the first cup, two from the second cup, and one from the third cup, and taste that. Repeat and taste with different ratios from each component.

I’d love to hear from you if you would like to share your experience with solubility matching and blending. Thanks for reading.

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