Hello to all home-barista crowds.
I would like to ask for an advice. With my mediocre skills and equipment (Oscar/Rocky) I can produce consistently good to great results with some coffees (Ethiopian naturals being my favorite with really smooth sweet dark fruit with chocolate tiger stripped shots) and also with more Italian style darker espresso blends with nutty/caramel shots. But with some coffees (to generalize I would say brighter/lighter fully washed coffees) I have tried all reasonable combinations of dose/time, and even when I go higher temp, lower dose, ristretto-ish pulls, I still get a lot of sourness in the taste. Those shots actually look underextracted, with quickly separating lighter crema, and this happens really close to choking the machine with no margin to move further to. Same coffee might be really pleasant and aromatic when cupped or on filter, no even very acidic to my taste, but when I try to pull espresso with this coffee, I have such troubles to dial in to.
PS: I am talking about fresh coffees (5-14 days post roast), from reputable roasters.

Try unreasonable combinations.

Actually serious, unconventional combinations anyway. I remember once accidentally pulling a light WP Yirg super uber ristretto, first drip was at about 30 seconds and what the heck let it go as in about barely 1oz (double basket) in 70 seconds - sweet syrupy lemons. Not the kind of pull I'd usually go for, lacked much dimension, but quite surprisingly drinkable!

The Rocky works well at low doses, as does the Oscar with its stock baskets. Both suck at higher doses. Stay with 12 to 14 gram doubles. Grind fine for a ristretto shot and give the Oscar a very long flush to get down to around 90C. The cool extraction will control the bitternees and sweeten the shot; the ristretto shot and fine grind will control the acidity an give you a full extraction.

You should experiment with other combinations; but on your gear, I think this might be the shot style most likely to succeed with difficult coffees.

Another tool I used when I was stuck trying to find a grind/dose that worked was to cut the shot early (or cut out the start of the shot). When I run in to a tricky coffee that I'm having trouble with I usually end up tasting the shot at different times during the pull (either just using a spoon to sample it while it pours, or using a few cups to catch different parts of the pour).

All coffees will produce different flavors between the begining of the shot when it's cooler and much more concentrated, and the end that's hotter and is carrying less solubles. But some will be drastically different, and I've had shots that were 2/3 great and then the last few seconds completely ruined it. Cutting the shot early - so the flow looks normal, but stopping it well before I noticed any visual changes - to end up with a ristretto amount in the cup, has gotten me some good shots from ticky coffee.

This might just be a shortcut to get around some mistake I'm making, or some limitiation of the equipment, but if nothing else it's an interesting experiment to do. Good luck!

Thank you for your thoughts and suggestions.

Following Jim's advice, instead of higher temp, lower dose, ristretto I have tried to do LOWER temp, lower dose ristretto. It definitely helped do get more enjoyable shots from direct trade Bolivian SO I have been struggling with recently.

I am still wondering why some coffees are enjoyable at wide spread of "variables" and others are so hard to hit sweet spot with.
Success also depends on allowance in variables within which given equipment can perform.

another_jim wrote:The Rocky works well at low doses, as does the Oscar with its stock baskets. Both suck at higher doses.

I would like to discuss this point.

After reading through this forum for almost a year now, trying all different techniques, I have ended with this routine for my Oscar/Rocky combo:
Grind - WDT - level the basket with straight edge of a ruler or knife (no downward tapping/chopping) - it gives me from 17 to 18 grams (depending on coffee used) in NS double basket - tamp and go
At this dose there is no imprint of screen/screw on a soaked puck after extraction. This described routine is my comfort zone and gives me best pours I can get, nice and smooth flow which stays dark long enough. Works like a charm with some coffees, but as I mentioned before, almost undrinkable with others...
As I move down with dose, my puck preparation suffers because I can not level the basket. Those 12-14 grams looks like just little bit of coffee powder somewhere deep at the bottom of the basket. Also it sends my grind very close to Rocky's true zero point. Most of such low dosed shots will blond early and/or channel badly...

michailza wrote:Those 12-14 grams looks like just little bit of coffee powder somewhere deep at the bottom of the basket. Also it sends my grind very close to Rocky's true zero point. Most of such low dosed shots will blond early and/or channel badly...

The bad taste at higher doses is not fixable; the problems with lower doses are easily fixed -- grind finer. If you need to grind at the zero point, there is some wobble, and you should use a teflon tape wrap to stabilize the burr.

Italian espresso machines, grinders, and baskets are designed to be used at 7 and 14 grams. They are easier to work at these doses, and produce more consistent shots. When th grind is fine enough, 14 gram doses are less likely to channel, even with the most casual leveling and tamp. With entry level gear, it is by far the best to use this does as the standard, and only go higher if the coffee is very flat tasting. Fully extracted espresso almost always tastes smoother and gentler, and the lower the dose and the finer the grind, the fuller the extraction.