difference does altitude make in jam-making?"
Anne and Sue,
When I make my jam, I cook it to 219° F (104°
C), but when my friend in Calgary uses the same recipe,
the jam fails. Why?
Submitted by Brian in Victoria
you aren't using commercial pectin, it's important to
test that the jam or jelly has reached its gel point.
The concentration of sugar required to form a gel is
usually in the range of 60 to 65 percent. Since sugar
concentration and temperature are related, the easiest
way to determine if a jam or jelly has reached the gel
point is to check the temperature with a candy thermometer.[JANET:
Link to candy section?] A 60-percent solution boils
at 217° F (103° C). So in Victoria (British
Columbia), which is at sea level, gelling takes place
when the boiling syrup reaches 217° F-221° F
(103° C-105° C).
At higher altitudes, however, atmospheric pressure is
less, so water boils at lower temperatures. This means
liquids evaporate more quickly. The syrup becomes concentrated
and reaches its gel point at a lower temperature. In
Calgary, which is roughly 3000 feet (915 m) above sea
level, gelling happens at about 214° F (101°
C). So when your friend in Calgary boils jam until it
reaches 219° F (104° C), it is overcooked. Too
much water has boiled away, leaving a sugar concentration
that's too high. The jam is likely to be gummy and sticky.
Colors may be darker, and the texture quite tough.
For others cooking at high altitudes, note the temperature
at which water boils at your altitude, and add 8°
F (4° C) to determine the gelling temperatures.
Or use the following as a guide:
feet (915 m)
F (101° C)
feet (1219 m)
F (100° C)
feet (1524 m
F (99° C)
feet (1829 m)
F (98° C)
feet (2134 m)
F (97° C)
Anne and Sue