No matter. Try again. Fail again. Fail better. -Beckett
Steps to Success
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Grind enough coffee to just about fill two “wedges” in the doser.
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Get some into the basket, maybe half, and then optionally lightly tap the PortaFilter on the table once or twice to “declump” a bit and settle the grounds:
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Fill to about level with, or a bit below, the rim. If you’ve tapped & settled, you’ll want the level lower before you start to tamp; if not, even with the rim is OK, as there will be more compression on tamping:
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Tamp…firmly but, especially, levelly. The tradition says ~30 lbs. of pressure, but the geeks will tell you consistency is more important than the exact pressure. The sweet spot with our setup seems to be to get the tamper shoulder at, or just slightly below, the rim of the basket.
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If in doubt about the amount, lock the PortaFilter in and then take it out - if there is an imprint from the shower screen screw, there is too much coffee.
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Scratch off a mm or two and polish with the tamper.
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When you’re ready to go, lock in the PortaFilter and push the left hand button to start the pump - it will ramp up and then be steady - push again to stop the pump and have your shot. Ideally, on starting the pump, there will be a few seconds pause before a thin trickle starts and you’ll get a double shot in 20-30 seconds.
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Unlock the PortaFilter and knock out the puck, rinse the PortaFilter. Use the brush to get grounds off of the shower screen and group gasket, then give it a last burst of clear water from the pump to rinse. Put the PortaFilter back so it stays hot.
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Check the water level and fill it with the pitcher from the filtered water at the sink, if needed. Oscar misbehaves if it runs out of water.
Extra Credit
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Heat Exchange machines like Oscar tend to super-heat the water that is waiting to go into the group when you start the shot well above boiling due to pressure in the boiler. Since the ideal temperature is somewhat below boiling, it pays to run a “cooling flush” of 3-5 seconds with no PortaFilter in place if the machine has not pulled a shot in several minutes (pretty much always the case here) You’ll see the initial burst of steam, then that will diminish. Start your shot within the next 30 seconds or so. Needless to say, this uses water up faster than just making a shot, so keep an eye on the tank and refill if it gets low.
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If your shot chokes, and only ever puts out a few drops, or nothing, rather than a few drop followed by a thin stream, stop and “do over.” That is usually a sign of over-packing/over tamping. If it gushes a light colored faster stream, you may have under-dosed or under tamped OR you got the dreaded “channeling” where the water under pressure finds one or two paths through the puck that have the least resistance - extracting way too much locally from the grounds as it goes and ignoring the rest. This can happen if the distribution of the grounds is uneven, the tamp is not level (one side thinner) or a crack in the puck or between the puck and the sides of the basket. If you’re pretty sure of the dose then, probably, you got some form of channeling. It’s tricky. The puck prep seems to be the crux of getting a good shot, there is not a lot else we can control on the Oscar.
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When you’re done, if the puck is sloppy and muddy, you could probably dose a wee bit more; if you see the screw mark, just barely, on the top of the puck you’re at the upper limit - (the puck will expand some and may push up against the screen when wet). It’s a pretty narrow window as far as I can tell, between too little and too much - I find that if I just barely see a mark from the screw and the pull was 20-30 seconds I’ve probably got a good coffee but ideally you get a good coffee without that print.
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It’s hardly ever perfect - too many variables - but it’s almost always pretty good.
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Double extra ‘spro-‘bro points if, once in a while, when you’re done, you pop the blank PortaFilter in and run the pump for five to ten seconds to “backflush” the machine - it clears Oscar’s sinuses and helps keep gunk from building up. I do this more systematically most Fridays, but it is good to do it occasionally in between as well.
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