Tasting both bitterness and sourness (with no sweetness) in your pour-over is a telltale sign of uneven extraction – some grounds are over-extracted (bitter) while others are under-extracted (sour)

If your espresso tastes sour or bitter, it’s usually an extraction issue: sour means under-extracted (you didn’t pull enough sweet flavors out)

Focus on a quality burr grinder first – it’s the unsung hero that can make even a basic machine produce great espresso