Should I stir the grounds in a Chemex?

A gentle stir right after pouring the bloom water can help ensure even saturation. Just avoid vigorous stirring that creates a mess or clogs the filter.

How long should a Chemex brew take?

For a standard 600g batch (about 3 cups), aim for 3:30 to 4:00 minutes from the first pour to the last drip. If it finishes faster, your grind is likely too coarse.

Can I fix sour coffee after it's brewed?

Not really. Adding a pinch of salt can mask sourness, but it won't fix the underlying extraction issue. Your best bet is to adjust your next brew.