The increase of renewables in the electricity mix is changing how power systems operate and adding new players to the energy markets. In a very short time, it is expected that aggregators can provide balancing services that leverage the flexibility of small and medium-sized consumers. This paper presents a study that assesses the potential of using professional espresso machines to provide Demand-Side Flexibility (DSF) services and, more concretely, Frequency Containment Reserves (FCR). The proposed methodology takes advantage of the coffee and steam boiler components of the coffee machine to identify opportunities to reduce the electricity demand, hence providing demand-side flexibility. The proposed methodology is evaluated using synthetic data generated from a dataset initially collected from an original professional espresso coffee machine during its daily operation. The results show that for a group of 100 coffee machines, the disposable power through the day would vary from 33 kW in the nighttime to 42 kW between 10 AM and 6 PM. The results also show that a minimum of 10 coffee machines are necessary to establish a non-zero disposable power and that after about 30 coffee machines are aggregated, the achievable disposable power becomes nearly linear.