Temperature control
Concentration matters.
Finish the syrup 5°C / 9°F above the temperature at which plain water boils in your kitchen.
105°C · 221°F
Sea-level target. At higher altitude, plain water boils below 100°C / 212°F. Measure your local boiling point and add 5°C / 9°F. Do not use 105°C automatically at high altitude.