So we’ve sourced the most amazing coffee, transported it with utmost care, roasted it to perfection, got it to you at peak freshness…now it’s over to you! No pressure, but don’t be letting us down.
The extraction method has a big influence on the character of your cup. Flavour is definitely influenced by brew method, but it’s hard to talk about it in isolation of technique and recipe, so first we need to get a little technical. In our next post we’ll bring it back to the brew method, but today we droppin’ science.
There are two important measures of coffee extraction – Total Dissolved Solids (TDS) and Extraction Yield. A refractometer helps take the guesswork out of your quest for the perfect cup, but a general understanding of these measures will help to make sense of why certain brew methods produce different tasting coffee.
Total Dissolved Solids (TDS)
TDS refers to the percentage of soluble coffee solids in your cup. This is the concentration of the coffee in water, and directly impacts flavour strength. Typical figures are about 1.5% for filter coffee and 15% for espresso.
TDS is affected by the dose of ground coffee, the volume of water in the cup and the brew method.
Flavours can also be categorized by their solubility in water. These categories were first named by Ted Lingle and are listed below in order of decreasing solubility:
- Enzymatics (fruit acids, florals) – most soluble
- Maillard compounds (nuts, toasted grain, malt, wood, tannin)
- Sugar browning (sweet, vanilla, caramel, chocolate)
- Dry distillates (burnt sugars, tobacco, smoke, ash) – least soluble
While presence of these flavours is related to the characteristics of the coffee, their varying solubility explains why the cup profile is changed by different brewing methods and roast profiles e.g. too long a steep time in your plunger will bring out more of the darker, ashy flavour in dark roasted coffees.
The extraction yield is the percentage of soluble coffee solids extracted from the dry coffee – this dictates the flavour profile in the cup. An extraction yield of about 20% produces the most balanced cup profile for both filter and espresso methods. Only about 30% of dry, ground coffee is water soluble; the remainder being cellulose. Coffee usually tastes best when about two-thirds of the available solubles are extracted.
The amount of coffee that is dissolved in the brew water is affect by:
- Size of the grind – this determines surface area of exposed coffee and the rate at which solubles extract
- Length of time the coffee is contact with the water
- Agitation (stirring)
An increase in extraction yield also causes an increase in TDS.
Bringin’ the heat
Temperature also affects extraction. The detail is important for espresso but in the interest of keeping it simple, lets just agree that the optimal coffee brewing temperature is 95°C, just off boiling. There is widespread historical agreement on this, and achieving a consistent brew temperature is relatively easy in most everyday brewing situations.
Having the brew temperature too high will introduce negative, bitter qualities.
Check yo’ self
As you experiment, taste the difference. Use the flavour solubility categories above to discern where you’ve arrived in the extraction spectrum. For filter and immersion methods adjust the grind, steep time or agitation (one at a time) to increase or decrease the extraction yield, and adjust the dose or water volume to affect the TDS and strength of flavour.
While there are a there are a number of things you can do to adjust the extraction and potential outcome, each brew method does have it’s own general flavour qualities. We’ll talk about these in the next post.