Operation principle of coffee machine principle of single boiler heat exchange

Since Luigi Bezzera introduced the first commercial coffee machine with steam pressure in 1901, whether Pavoni Gaggia or other machines using steam or piston as pressure, there has been only one boiler: the boiler below provides hot water for brewing coffee, and the boiler above provides steam. However, in order to make steam, the whole boiler must be heated to boiling point, so that the hot water near the boiling point burns the coffee powder, loses the aromatic oils hidden in the coffee powder, and extracts the coffee with double bitterness.

Since the water for brewing coffee is heated in a large boiler, the water will not be fresh after being placed in the boiler for too long, and the temperature difference of the hot water will increase due to the use of steam, and the temperature difference of the hot water for brewing coffee will also increase due to the different amount of steam.

In order to improve the temperature difference, Ernesto Valente changed the heating method of the water used to brew coffee in the FAEMA E61, the world's first pump as a source of pressure, in 1960, so that the brewing water does not directly contact the heat source, but uses a method similar to water insulation heating.

The boiler of FAEMA E61 (hereinafter referred to as the outer boiler) has a pipe (hereinafter referred to as the inner pipe) in the middle, which uses pumps to introduce fresh cold water into the inner curved pipe. When the pump pushes fresh cold water through this pipe, the cold water is heated by the hot water in the outer boiler, but the outer pipe is wrapped so that the fresh water does not come into contact with the hot water in the outer boiler. The inner water pipe is curved so that the cold water has enough time to contact the outer boiler to reach the hot water temperature just suitable for brewing coffee.

(See below, this picture is a bit simple)

- ------Vapors

│ ┌- →

│ │

- <$^^^^^^^^^^^^

Cold Water--

→ -┬ ┬-┬-┐││┌-┬-┐│

-

pump │ └--┘ │

│ │

│ │

└------┘

boiler

Because of the circulation of hot water in the boiler, each cup of coffee is brewed at a very close temperature, whether it is one cup in an hour or a hundred cups at a time. In this way, not only can the temperature difference be reduced, but also the freshness of the water is taken into account, and the hot water in the boiler is only used to generate steam for making milk foam, and will not be used to brew coffee.

This is the principle of the single-boiler heat exchanger, until more than 30 years later, the internal structure and principle of most Italian coffee machines are still very close to FAEMA E61.

From the above explanation, we can infer that the larger the capacity of the external boiler, the lower the temperature difference of hot water brewing coffee, the more it can reduce the temperature difference caused by the use of steam.