An employee checks freshly roasted coffee beans during cooling down in a tumbler at H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018. REUTERS/Arnd Wiegmann

An employee looks at freshly roasted coffee beans cooling down in a tumbler at H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

A tourist takes a picture through the open window of H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

People look through the open window into H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

An employee took out some coffee beans from a drum type roaster to check the degree of roasting at H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

Freshly roasted coffee beans cool down in a tumbler at H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

Freshly roasted coffee beans fall into a tumbler after the drum type roaster is opened by an employee at H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

Tourists look through the open window into H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.

An employee checks freshly roasted coffee beans during cooling down in a tumbler at H. Schwarzenbach coffee roastery in Zurich, Switzerland December 4, 2018.