What does a higher TDS reading generally indicate about the espresso?

A higher Total Dissolved Solids (TDS) reading in espresso generally indicates that the coffee has been over-extracted. TDS measures the concentration of dissolved solids in the brewed coffee, which includes soluble compounds from the coffee grounds. When the coffee is over-extracted, more of these solids are dissolved into the espresso beyond the optimal extraction point. This often leads to a cup that has an imbalanced flavor profile, typically featuring bitter notes due to the extraction of undesirable compounds.

In contrast, an under-extracted espresso would yield a lower TDS reading, as not enough of the soluble materials (like sugars and acids) have been extracted. A low brew ratio refers to the coffee-to-water ratio used in the brewing process, which is more about the balance of coffee concentration rather than the extraction quality indicated by TDS. Under-frothing relates to milk texture and does not directly affect TDS readings in coffee. Understanding TDS is crucial for baristas aiming to perfect their espresso shots, as it directly correlates with the quality and flavor of the final product.