If the coffee powder is not fine enough,the espresso extracted would be acid,the color of the espresso would look like that of meat.
If the coffee powder is too fine,the espresso would taste more bitter,and the color become brown.
Luckily, the espresso powder has standard parameter:
60ml espresso can be extracted within 20-30 seconds.
If the powder is too fine, or not fine enough, to adjust according to this standard is OK