Wait, instant coffee extract? That is...not espresso
edit: ok, they pulled espresso shots and freeze dried them in the lab (lol) -
"The espresso coffee extract was obtained from 15 g of powder using a two-cups coffee machine (Gaggia espresso machine, Gaggia Milano, Italy) for a final volume of 80 mL of beverage. The extraction lasted for 30 s at 80 °C in mQ H2O. The final product was distributed in 15 mL Falcon tubes, freeze-dried, and stored at +4 °C."
Perhaps they measured the temperature of the espresso shot post extraction, in the cup (or more formal receptacle!), where it would be cooler than the water meeting the ground coffee.
Also, a Gaggia Classic (as an example - they don’t specify which model they use) does not have a PID. Temperature of the espresso leaving the group head drops during the extraction.
edit: ok, they pulled espresso shots and freeze dried them in the lab (lol) - "The espresso coffee extract was obtained from 15 g of powder using a two-cups coffee machine (Gaggia espresso machine, Gaggia Milano, Italy) for a final volume of 80 mL of beverage. The extraction lasted for 30 s at 80 °C in mQ H2O. The final product was distributed in 15 mL Falcon tubes, freeze-dried, and stored at +4 °C."