With the hopper on:
Does the concept include partially ground beans still between the burrs when the motor stops?
How about whole beans below the hopper door, but untouched by burrs?

BDL

My understanding is:

The definition may be determined by the usage. The "retention" is universally defined as ground coffee stuck in the grinder that didn't make it out.

For purposes of single dosing, my understanding is that it is starting with a clean grinder, running a set weight of beans through it and weighing the output. The difference is the retention or expected stale coffee in the grinder. What I have not seen in the description so far which may have been brought up is the amount that comes out on the second single dose. Some coffee may be retained and fill in gaps of the machine but does not come out in later doses.

For full hopper use, I see this as the amount if stale coffee that has to be purged before getting to the freshly ground beans. A user does not have the luxury of bumping the extra coffee out because it will just grind more coffee.

My understanding would be :- weigh what goes in. Weigh what comes out. Subtract one from the other = grind retention.

+1

walshman wrote:My understanding would be :- weigh what goes in. Weigh what comes out. Subtract one from the other = grind retention.

Swell. But totally unresponsive to the specific questions asked in the OP. Also, not very easy when working with a hopper instead of single dosing.

I'd get mad and tell you that I'm not an idiot, but since I am an idiot it would cause further confusion.

In the interests of better comprehension, the thread title was edited. Also... The definitional questions go to the practical question of how much to clear from my new grinder every morning.

BDL

Assumption 1: The goal in defining retention is to reduce shot-to-shot variance by ensuring that one is using freshly ground coffee for as much of the dose as is possible.

Assumption 2: Partially ground beans stale faster than unbroken ones, but unbroken beans sitting below a hopper door are staling at the same rate as beans sitting above the door.

Conclusions: Anything the burrs have started to break counts as "retention," and should be purged before a session. Anything beans that are still above the burrs, no matter how close they are, do not. Obviously, any coffee that has already been ground, and is sitting in a chute waiting to get pushed out by the pressure of further grinding, also counts as "retention."

Based on extensive past experience with this topic, I doubt you will get consensus on a definition of grind retention. Some folks claim it is every coffee particle you can pick out of the grinder, including partially ground bean fragments in the burrs, compacted grinds in the grind chamber, etc. I prefer a more useful working definition, along the following lines: how much previously ground coffee ends up in the subsequent doses.

This is not a precise definition. For example, consider partially ground beans: large bean fragments wedged in the burrs will not stale as quickly as fully ground particles remaining in the burr chamber or chute. How shall we handle these? In addition, retention may vary from dose to dose, especially if grinds are not brushed out of the chute.

Nonetheless, this is a practical definition of grinds retention. No matter how much coffee is retained in the grinder, only previously ground particles (which presumably stale faster than unground beans) that end up in your subsequent doses, will have an impact on subsequent extractions. This is the amount you should be concerned with, and provides an upper bound on how much coffee to purge at the start of a session.

I have a simple solution to the grinder retention problem. Almost all of us have a wife/husband/so/roommate/whatever living with us that is not nearly as into coffee as we are. Give the first shot of the day to them. They think we're being polite, and we get fresh coffee.

I don't leave beans in the hopper, but if I did, how long do you guys do that? I assume some aging is acceptable but I'm freezing everything at the supposed optimal age post-roast date right now.

I single dose a pharos these days, but when I used my mazzer mini I kept roughly a weeks worth of fresh roasted coffee in the hopper. Seemed to work fine. IMHO if your coffee is fresh it produces enough CO2 to protect itself from short term harm. Obviously if you're going to try to store longer term you should probably try something fancier.