Why did my roasted pumpkin soup smell foul and seem sour after only 1/2 day? I made 2 batches of roasted pumpkin soup and both went sour and smelt horrible within 1/2 day.  I am unsure why and am baffled as I have made soups heaps of times, but not this roasted pumpkin soup.
Were there a lot of onions in the soup? My uncle was a chef and he said that you should never put onions in soup as it would add a sour flavour.