Let me preface by saying I clean my machine every day. I only use filtered water. Machine: Morphy Richards Fresco (Standard drip-coffee)
I use coffee grounds (medium roast). I don't know the grind. I buy the grounds from a local coffee shop.
When I make four cups (max capacity). basically filling the grind in the metal filer to "4-cups" mark (max).
, 3/4 of the way: The coffee pours at a reasonable rate till it becomes extremely slow. Only drops are coming out. Then finally like a pressure cooker, the coffee pours out a rapid rate. It has a sort-of burned smell to it. The coffee still tastes good.
The same does not happen when I fill the filter for 3 cups.
I find the 3-cup brew slightly less bitter, it has greater natural sweetness.
I can not tell why.