There is no one right answer for dose, but let's look into why we might want to change our dose.
Dose: The amount of coffee ground that is required in the coffee basket
To start, how do we know that we are using an incorrect dosage?
Check for consistency in your coffees. If you are finding that they are varying in flavour shot to shot, then it's a great time to check your dose.
A good place to start is to check your basket size. You will match your basket size with your coffee dose. For example, if your basket size is 20g, then match this with 20g of coffee grounds.
As I said, this is your starting point. Next, we want to ask ourselves how do we want to represent this particular coffee bean. Are we looking to bring the focus to the more delicate, intricate flavours, or are we looking to increase the texture and the weight of this espresso?
Typically for single-origin profiles, I would want to preserve those fruity, floral and delicate flavours that represent that region of coffee.
However, if I am looking at making a milk-based coffee, I know that a lot of those flavours are going to be lost in the milk, therefore I would be wanting to increase the texture and richness of the espresso shot, to allow those caramel and nutty flavours to still transfer through the milk.
Another way to look at it,
The lighter the roast: the smaller the dose
The darker the roast: the larger the dose
This is because a lighter roast will break down the coffee less (making it less porous) and as such making it harder for water to find and extract from the pores, therefore less dose will allow more water contact and more opportunity for extraction.
One last thing to note,
The water coming through will try and find the path of least resistance. This is why it's important to ensure that the distribution of your grounds in the basket is even. This may present as coffee coming out of one spout and not the other. The result of this is a mix of under-extracted and over-extracted coffee.
This is called 'channelling'.
If you missed out on the other 2 blogs in this series, check them out here.