What is the difference between a double espresso and a lungo in terms of TDS?

In the world of espresso, the relationship between brew ratio and Total Dissolved Solids (TDS) is the primary lever for controlling strength. A standard double espresso, typically prepared at a 1:2 ratio (e.g., 18g of dry coffee yielding 36g of liquid), sits in a concentration sweet spot of 8% to 12% TDS. This concentration provides the syrupy body and intense flavor profile that defines the classic espresso experience.

A lungo, by contrast, is an 'extended' shot. By pushing the ratio to 1:3 or higher, the barista forces more water through the same puck of coffee. While this extra water does pull more total mass from the grounds—potentially increasing the total extraction yield—it simultaneously dilutes the concentration of those solids. Consequently, a lungo typically registers a lower TDS, often falling into the 4% to 8% range. This dilution is why a lungo feels lighter and less viscous than a standard espresso.

It is important to distinguish between strength (TDS) and extraction yield. A common misconception is that a higher TDS always equates to a better or more 'extracted' coffee. In reality, a ristretto might have the highest TDS of all, yet it is often under-extracted because the water contact time is too short to pull out the full spectrum of desirable compounds. Conversely, a lungo may achieve a high extraction yield, but the extended contact time can pull out bitter, astringent compounds that were better left in the puck.

In practice, the choice between a double espresso and a lungo is a trade-off between intensity and volume. If you prefer a bold, punchy shot, the standard 1:2 ratio is your baseline. If you find that ratio too intense or are looking for a longer drink that still retains some espresso character, the lungo offers a more approachable, albeit less concentrated, profile. Always remember that TDS is a tool for consistency, not a definitive measure of quality; your palate remains the final judge of whether the extraction balance is correct for your specific beans.