Today's research (mainly revolving around Jim Schulman's "Value Subtracted Espresso" - https://docs.google.com/file/d/0B5Jq6uZ ... edit?pli=1) leads me to present the following hypothesis:

Basket size dictates the other variables

Here is why I am inclined to believe so:

1. Shot time
   Let's agree to aim for a (double) shot that starts blonding at 27 seconds. (Or any value you fancy.)
2. Shot weight
   We want to obtain a certain weight in espresso during this time. (Precise value again not important.)
3. Dose
   Our basket directly dictates the volume we dose. (Sure, the machine matters, but let's leave that as a constant.)
   People here seem to agree that the headspace should just barely allow for a 2mm coin between the screen and the puck. I concur, as I tend to get channeling if I leave much more headspace than this. As such, the basket dictates the volume we need to dose.
4. Grind
   Now we have one variable left to adjust: grind size. Since we said we required a 27-second shot of a set weight, we will need to adjust this variable to obtain that result.

(Sidenote: I have left out distribution and tamping technique. For the sake of argument, let's say we can take as much time as we need, and these are optimal. Temperature has been left out as well, as I'm assuming that a certain temperature is recommended for the given beans.)

So we have used our available variables to get a 27-second shot of the desired weight, and found that there was only a single combination leading to it.

What if we want to change the taste balance of the shot (e.g. make it sweetier with more caramels) without affecting its other properties?

"Grind alone (once the shot flows properly) determines the taste balance." (Jim Schulman)

But if we now change the grind, we change the flow rate! Compensate by adjusting the dose? Can't - our headspace will change.

I conclude that the basket has fixed the other variables. In order to change the balance of the shot, we need to use a different basket.

Have you found the same thing? Are your results to the contrary? I invite you to share!

To illustrate:

Today I made a shot in my 18g VST basket. I had dosed 17g and the shot was very tasty, but a bit too aggressive. I ended it as a 35-second ristretto, but it had not even started blonding at the 35-second mark.

So, I wanted to adjust for a faster-flowing shot, but dosing any less destroyed the puck. Perhaps I should use a coarser grind...?

I also wanted to extract more caramels. Perhaps I should use a finer grind...?

So I need a finer grind for the right taste balance, and I need a smaller dose for the right flow. But I can't seem to manage a smaller dose in this basket. Because of this, the basket seems fixed to a certain ratio between flow and balance. I can get a faster flowing, more pronounced shot (coarser grind). Or I can get a slower flowing, sweeter shot (finer grind).

To achieve what I am looking for, I need a smaller basket!

I have ordered a 15g VST today. I'm also looking forward to reading your thoughts.

Basket size doesn't dictate the dose nearly as much as you seem to think, at least not in the general case. I make shots using anything from 12g up to 17.5g of ground coffee in my MCAL double baskets without trouble. Of course, some baskets may be trickier than others in this respect; back when I used them, I recall the VST baskets being more finnicky.

Likewise, there is no reason that you must hold either beverage mass or overall extraction time constant when pulling shots. Rather, you should be dialing them in to get the best taste out of your shots, which will vary based on coffee selection, roast level, and user preferences. If a 40s ristretto tastes good, except that it was a bit too aggressive, then downdose and tighten the grind a bit to adjust for that, and don't worry about the time or beverage ratio.

Yeah, they say the VSTs are finicky, although they do claim this is with good reason.

If a 40s ristretto tastes good, except that it was a bit too aggressive, then downdose and tighten the grind a bit to adjust for that, and don't worry about the time or beverage ratio.

I will see what happens when I loosen the weight and time constraints. I'll try downdosing and grinding finer again - see if I can manage it without crreating an uneven extraction, althought that was the main problem so far.

Where I work, we use 17g "Strada" VST baskets for espresso. Regularly, doses for our blend in these baskets are ~20g, sometimes as high as 21g and almost never less than 19g.
I don't necessarily agree with the fact that we use these baskets with these doses (nor does the puck with its never-failing dispersion screw imprint), yet this manner of use functions perfectly well and makes us tasty espresso.

Rules are overrated.

another_jim wrote:Good idea; but, baskets have three key variables: absolute size, par dose, and d(flow)/d(dose) As mentioned, VST baskets have such a high d(flow)/d(dose) that they are finicky.

Jim, could you explain this a bit further? The thread you linked to I've read before, and it's somewhat beyond me. Can you explain the meaning and effect of these key variables in layman's terms?

Meanwhile, I'm getting decent results with the VST baskets. I'm dosing 14g in the 15g basket, and 16g in the 18g basket, adjusting grind for a proper bottomless extraction. The 14g tastes balanced, and, depending on the coffee, may or may not be lost in milk (flat white). The 16g tastes aggressive to my taste, and either better or still overly aggressive in milk, again depending on the coffee.

Timovzl wrote:I'm dosing ... 16g in the 18g basket, adjusting grind for a proper bottomless extraction. The 16g tastes aggressive to my taste, and either better or still overly aggressive in milk, again depending on the coffee.

The picture you're painting for your readers is incomplete. You've given us your doses but not your brew ratios.

Whether the pf is bottomless or spouted should not affect dosing. Try dosing the 18g basket at 18g-19g, and adjusting time -- by coarsening your current grind -- to a "standard" flow rate of 25sec - 30sec to the blonde point for your desired brew ratio.

For any given coffee, a high brew ratio (e.g., ristretto) will be more "aggressive." If you want less punch, grind coarser and pull a lower brew ratio (e.g., normale).

The dose range for an 18g VST or 17g Strada basket size is no more than 2g. For example, in my machine, the "right" dose was 17.5g - 19.2g.

Rich