Q: Why does my espresso taste bitter when it's cold outside?

Cold air chills your machine's metal parts and water lines, so the water hitting the coffee might be cooler than normal. That leads to under-extraction, which can taste sharp and bitter, not sour. Also, if your portafilter is cold, it steals heat from the shot as it extracts.

Q: Should I grind finer or coarser in winter?

It depends on your shot time. If you're getting a fast, bitter shot, grind slightly finer to slow it down. If the shot is slow and bitter, grind coarser. But first, check your water temperature—if it's too low, grinding finer just makes things worse. So, warm up your gear and check temperature before changing the grind.

Q: What water temperature is best for espresso?

Around 195°F to 205°F (90°C to 96°C) is the sweet spot. In winter, your machine may struggle to hit that, so let it heat up longer and flush some water through before pulling your shot.