Single vs Double Baskets
An important discovery made by early proponents of the coffee refractometer was that single espresso baskets, in the region of 20% extraction yield, are less efficient than double baskets. Where a double basket is delivering 10% TDS from a 16g / 32g recipe, in halving the recipe but keeping the same ratio for a single basket (8g/16g) the anticipated TDS would only be around 8%. This could be due to water channelling down the edges of the single basket. A higher basket-edge-to-coffee-grinds ratio with single baskets will also contribute to channelling.
Double and single basket cross-sections
Although single shots may lead to low TDS shots and under-extraction, using a double shot basket, but splitting the shot with a double spout, is a solution to the problem of serving efficient single shots. However, doing this can lead to a lot of spare shots lined up on the bar, when only one single shot has been ordered. The shelf life of a spare espresso is also debatable. In blind tastings with shots rested an hour, we have observed no obvious deterioration in the flavour of milk drinks made with these older shots.
Bringing up Single Shot Extraction Yields
When switching between single and double baskets, the only means of obtaining parity in extraction yields is to use more water to brew single shots in order to increase the extraction yield. This comes at the expense of body with the single shots drifting into the lungo strength range.
It’s worth noting that the increased solubility of most darker roasted and/or second crack coffees may see single baskets produce a nicer tasting, more balanced flavour than double baskets. This is a case of ‘full extraction’ leading to undesirable flavours. A lower extraction can limit these undesirable flavours. Equipment promoting less efficient extraction rates can potentially be beneficial in this scenario also.