When the mercury climbs, your siphon brewer doesn't suddenly change its personality. But the environment around it does. Hot air means:

• Your water reaches boiling point faster and can stay there longer, which messes with the extraction temperature sweet spot.
• Your grinder's burrs heat up, leading to more fines and an uneven grind.
• Your beans stale quicker, losing the delicate sugars that balance acidity.

All of that pushes your brew toward under-extraction—and under-extraction tastes sour, like biting into a lemon when you wanted a caramel note.