The initiative, passed on Wednesday by 71 votes to 41, stipulates that at least 50 percent of the offerings must be organic.
It applies to retirement and care centres, hospitals, day care centres, schools, canteens and cafeterias.
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Environment and Health Director Andreas Hauri acknowledged that there may be some problems in converting over to organic food, but said he was “convinced we can still increase the proportion”.
The city said it will now begin to examine how it can boost the proportion of organic foods to the required levels.
The city’s nutrition strategy already calls for a greater amount of food from the surrounding region, but had previously been silent on the amount of organic food that should be included.
While the initiative passed, there was some opposition from the right-wing Swiss People’s Party (SVP).
The SVP said the change was “far removed from decency and reality”, arguing that it sent the wrong signals to developing countries.
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The initiative is “an affront to people in poor countries who do not know how to feed themselves” said the SVP’s Johann Widmer.
The Free Democratic Party (FDP) also opposed the change, saying it was unclear how the new standards would be implemented.
Martina Zürcher asked how the 50 percent requirement should be measured.
“In kilograms? In francs?” she said.