It has an effect, and quite a bit, especially with winter stores (preserves) that are thermally processed in water or in the oven.
The main problem is that water at a higher altitude boils at a lower temperature. At sea level, boiling is about 100 °C (322 °F), but the boiling temperature decreases as the altitude increases.
That's why the altitude can affect:
- the pasteurization time of the jars
- time of cooking or processing vegetables and fruits
- winter stores - preserves safety
- evaporation of water and concentration of syrup or brine
- the time required to reach the appropriate temperature in the jar
