Single dosing is the practice of only putting in enough beans in a grinder to make a single shot of espresso. The idea is that you decide what coffee you want to drink, how much you want in a given dose, you measure it out, put it in the grinder, and grind getting exactly the dose you wanted.
Why is this a subtle issue and not just clearly a win – win situation relative to dumping a load of beans into the grinder and having to figure out how to start and stop it to get the dose you want and not more or less?
It turns out both strategies have advantages. Large grinders that are used in cafes are designed to work with a load of beans on them, not for single dosing. Coffee hobbiests have found that large grinders like the super Jolly, Robur, etc help home baristas make much better espresso at home than they can make with cheap grinders. The column of beans applies even pressure feeding the beans into the grinder making a predictable, more even grind.
On the other coffee shops go through many pounds a day while home users do not so it makes more sense for a café to have more beans in a grinder at a time.
Also if you want to change coffee frequently you don’t want to have lots of beans in the hopper, and if you want to fit a huge grinder into a home kitchen you may want to take the hopper off entirely.
I love to switch coffees at least once a day and sometimes more often, so I am strongly pulled towards the convenience of single dosing. It turns out different grinders behave differently under single dosing. Every grinder changes as the load lightens, but some are much better at single dosing than others, for example the Super Jolly does much better than the Cimbali Max Hybrid in this context.
I think the key is how consistent the inconsistency is for a given grinder. If the particle distribution is about the same from one grind to the next (although less uniform within a given dose than under a large load of beans) I think single dosing works fairly well. This is just speculation but it seems to make sense as you cannot dial in a grind if the beans come out totally differently every time. This is one thing I think people often overlook when they are learning and that makes their learning curve much longer.
Single dosing is a big enough topic that it cannot be contained in a single post, so I will continue with part two later…
Edit: to add link to part two now that it has been written.