I have a Baratza Vario, and I've noticed something interesting about the interplay between the grind setting, timer and dose weight.

Normally, I dial-in the grind for a particular dose weight (+/- .1g), then set the timer to produce that weight. The Vario is pretty consistent at producing the same weight for a given timer setting, usually within .2g. When the coffee is fresh, a given time setting will produce the target weight several days in a row.

But as the coffee ages, the amount of coffee produced by the Vario at a given time setting changes, as you would expect. For example, yesterday the grind time on my Vario was set to produce 16g. But this morning, at the same grind setting, the grinder produced about 17.2g. I scooped out about 1.2g of coffee and ran the 16g shot. But it was too fast, about 20 seconds. Clearly this was due to aging of the coffee. So I made the grind finer, but kept the timer setting the same. This time the grinder produced about 16.7g of coffee with the previous timer setting. This makes sense: for any given time value, a coarser gind will produce more weight than a finer grind. I pulled a shot, and it was still too fast, 21-22 seconds or so. Then I tightened up the grind so that the resulting dose was 16g. This time the shot ran the same as it did yesterday, around 27 seconds, and it tasted good, comparable to yesterday's shots.

Normally, with any grinder, I would adjust the grind setting until the resulting shot has the desired volume and blonds at about the same time as a good shot produced the previous day. But it appears that instead I can simply adjust the grind to produce a certain weight of coffee at the previously-set timer value, and I'll get very close to the same result.

This was not an isolated event. I've seen the same thing over and over, as the coffee ages: If I adjust the grind to produce the same dose weight as the day before, and keep the timer value constant, the resulting shot volume/time will be the same as or close to the day before.

I'm wondering if this makes sense to the experts. For a given coffee and set of shot parameters, is there a tight enough relationship between the grind and dose weight to be able to adjust grind for a particular weight using a reasonably accurate timed grinder? Something tells me it shouldn't be a linear relationship for all coffees, but the evidence here so far suggests it is.

[Disclaimer: I'm not saying this is the optimum method for determining the correct grind setting, nor am I suggesting that it's better to adjust only the grind (rather than dose, or both) as the coffee ages. I'm simply wondering if this method makes sense from a coffee physics point of view]

I don't monitor grind time, so I cannot comment on that. I do monitor grind setting and dose weight.

The tradition has been to keep dose constant and set the grind finer as the coffee ages. I no longer do that. As the coffee ages, it loses some if its more volatile high flavors. Setting the grind finer is exactly the wrong response, since this also favors the less volatile middle and low flavors. So now I up the dose as the coffee ages, and if I change grind setting at all, it's to go coarser.

If aged coffee really does grind faster than new; dosing by a fixed grind time rather than fixed weight is a sweet way to implement this better approach.

another_jim wrote:If aged coffee really does grind faster than new; dosing by a fixed grind time rather than fixed weight is a sweet way to implement this better approach.

Funny you should say that, because after I posted it occured to me that maybe I should just leave the dose as-is and see what happens to the shot parameters. In other words, when my 16g dose at 11.5 seconds turned into 17.2g the next day, perhaps the larger dose was just the ticket for reproducing the good shot from the day before. It would seem almost magical that this could be the case, but I shall endeavor to try it next time I see the dose weight change significantly from the day before.

Obvoiusly there can be limits to this approch if the dose starts bumping up against basket/machine limits.

The other thought that comes to mind is that what I've observed may be peculiar to the Vario. I would think it requires a timed doserless grinder with minimal retention and consistent output, and as yet there aren't many grinders like that on the market.