If your coffee is too strong or weak
Check your yield
Yield (the weight of brewed liquid coffee - an espresso shot), is often referred to as output. As you increase your yield, your strength decreases. - A shot with higher yield means more water is passing through the coffee – this increases extraction. More water also means the espresso is more dilute (decreased strength).
As you decrease your yield, your strength increases. - A shot with lower yield means less water is passing through the coffee – this decreases extraction. Less water also means the espresso is more concentrated (increased strength).
Choose your timing
Time, being the amount of time the coffee is in the contact with water is critical. Changing the time in which an espresso shot pulls can slightly increase or decrease both strength and extraction simultaneously.
Changing your grind setting gives you the ability to choose what time your target yield is achieved. A coarser grind creates less resistance in the basket and a faster flow of water (less strength and extraction). A finer grind creates more resistance in the basket and a slower flow of water (higher strength and extraction).