Dark substance on top of crema- ok?

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eastbaysanfranman
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#1: Post by eastbaysanfranman »



New to Mr. Oscar and new to 2 lbs. of fresh Redbird espresso. I typically get this dark oily substance on top of my crema. Is this inherit in this blend or am I not cooling enough and this is the dark oily ring which Dan referred to when superheated water comes partway through the shot (thus I did not do long enough of a cooling flush)

Second part to this question- I'm using a thermometer with a k-type thermocouple with a bead at the end. I ran the wire through the single spout of my second portafilter and taped it on so that the bead is at the bottom of the male threaded outlet of the portafilter. I then put the basket in so that it will slow the water down enough to let the water hopefully pool a little bit around the bead. I use this portafilter to do my flush until it reads about 196. Then I take my other portafilter which is already prepped, lock n load (about 15 seconds later). Is this a good method or am I using wrong equipment/technique? Is the water possibly hotter when it hits the puck and I am way off, making the dark oil you see here? I have read that the beaded k-type is not typically made to get wet.

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HB
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#2: Post by HB »

How much coffee did you use and how much did the resultant espresso weigh (i.e., what is the brew ratio)? How did it taste? I'm betting it's a combination of too high a brew temperature and underextracted. Grinding coarser and flushing longer should help.
Dan Kehn

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cannonfodder
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#3: Post by cannonfodder »

Taste would be the big indicator. Some coffees produce a bit of flecking and it is not a bad thing. If your temp is too high you get a burn aroma from the crema and the coffee will have an ashy bitter taste to it.

Crema solid tone vs. dark to light rich speckled tone ?
Dave Stephens

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uscfroadie
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#4: Post by uscfroadie »

HB wrote:How much coffee did you use and how much did the resultant espresso weigh (i.e., what is the brew ratio)? How did it taste? I'm betting it's a combination of too high a brew temperature and underextracted. Grinding coarser and flushing longer should help.
Dan,
Don't you mean overextracted?
Merle

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HB
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#5: Post by HB »

Er, I get underextracted and overextracted confused all the time. :?

If the espresso has a dark crema, slow pour, and low volume, it's extracting only the initial third of the "rule of thirds" test. If the pour pour quickly and blonds, the portion of coffee that was extracted was fully extracted and then some, i.e., all three thirds were extracted with emphasis on the last third.

I frequently write that overextracted = dark and bitter, underextracted = thin and sour, which is the opposite of what I imply above. :roll: Here's what Jim says:
another_jim wrote:Underextracted coffee is sour and thin; overextracted coffee is weak, with bitter and acrid notes. As the ground coffee extracts, the water flowing through it colors less and less. So the color is a measure of the degree of extraction and stopping at the same color means stopping at the same level of extraction. Perfect extraction occurs when 20% of the ground coffee's weight has dissolved into the coffee. Knowing the color that corresponds to this so you can stop the extraction means getting the best espresso for a given pull every time.
I suppose my inconsistency is rooted in the ambiguity of the frame of reference, the extraction of the coffee actually touched by water versus the potential coffee solubles that could have been extracted.
Dan Kehn

DanoM
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#6: Post by DanoM »

Dan (& Jim)

That's a great & informative post there. Got some more studying to do!!!
LMWDP #445

eastbaysanfranman (original poster)
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#7: Post by eastbaysanfranman (original poster) »

Ok, so it's been a long day with the Oscar. (wife glared at me a few times). I'm not sure what the brew ratio was on the first shot but I believe it was in the ballpark. Also can't recall the taste too well, I'm REALLY a newbie and need more time to develop my palate. Today was a day I decided to focus solely on temperature. I started placing the bead of the thermocouple on top of the puck to see what was happening during an actual shot. (found out that you HAVE to use fresh coffee every time- tried to be cheap but the subsequent pulls just ran straight through). So a few hours later this is what I found out: My Oscar climbs in temperature an average of 2.25 degrees F for every 5 seconds while pulling a shot. The other thing: it is surprisingly consistent. So in a 30 second pull the climb is around 13 to 14 degrees! So I figured I need to flush down to 181 degrees F (preparing my coffee while flushing) give myself 30 seconds to finish tamping which should bring the water up to 186 degrees F (The water temp rises slower when it's not extracting a puck, I figured 5 degrees in 30 seconds earlier in the week yet I need to verify, in the ballpark nonetheless) and then start pulling. That's right, at the low, low temp of 186. As it begins extracting a 30 second pull the temp rises to 199 - 200. There's something wrong that I have to start pulling at that low of a temperature in order to prevent overheating. I don't know exactly how they work but I have been recommended to get the Musica gliceurs (restrictors) so I won't have to flush as much water and hopefully prevent me from having to pull in such a wide window. Here's a picture of the setup I've been using to confirm temps with one portafilter before I would lock n load with the other one:



Look ok? I placed the bead close to where the WBC recommends it so I thought that would be cool but I wasn't sure if I should use a basket or not. Here's a picture of the shot when I finally got everything dialed in with my above formula as well as timing right on the money and a calibrated 30 lb. tamp as well as 16 grams in 30 grams out.



Looks a little better but still too much darkness. I paid much closer attention to the taste of this one and it was slightly bitter, a little chocolately but the sweetness of the coffee had been completely overcome. I had switched to my Gaggia basket as I heard that the Nuova Simonelli ones were a PITA (whatever that means exactly) to use. I also started dosing what is recommended by Gaggia for the basket which is 16 grams max. Anyways with the down dosing I've noticed that I'm having a rough time looking at the fact that the puck turns into a watery mess! Like a tsunami hit it, all discombobulated. So I am thinking that my group pressure is set too high. Anyone? If so I may need to install an adjustable OPV.
If I need these mods I don't think I even want to mess with the Oscar until I get them installed. I'll have to drink Redbird french press for awhile, which was delicious btw.

Here's a link to Sweet Marias page which shows different extractions (which you guys were so kind to lead me toward)

https://www.sweetmarias.com/library/con ... ghty-crema

You'll notice an exact picture of my shot above to where in which Tom refers to as over extracted :) and tells me the same thing, grind coarser. Last question, I could grind coarser but that would mess up my timing. Unless of course I should have been starting the timer at the push of the button instead of at the first drip, like the Redbird site says. Anyone?

eastbaysanfranman (original poster)
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#8: Post by eastbaysanfranman (original poster) »

So my above questions in a nutshell:

1) Has anyone else had the experience of an Oscar rising 13 - 14 degrees in a 30 second pull? (I'm going to be doing more testing to verify this btw) If this is true about my machine I'm assuming this would make for fairly bad espresso no matter what I do. Also, does anyone have experience with the gliceurs and where is a good place to source them in the USA.

2) What is the correct way to test pump and head pressure as well as head temperature? I can't seem to fine a straight answer on this except to get a scace. Is attaching a gauge to the portafilter and reading max pressure good enough? When I'm told that espresso is better extracted at 8 - 9 bar and the Oscar comes set at 14 bar, does that mean max pressure? I need to find out where I'm at before I decide to install an adjustable OPV. If you could be specific on what equipment I should purchase then that would be awesome. Having a 14 gram puck just get obliterated into mud makes me not want to use the Oscar until I get this figured out.

3) In timing my shots, I have been starting at the first drip. It has been taking 7-10 seconds for this to happen. I would concur that this is consistent as evidence which Dan pointed out that I probably have been grinding too coarsely. Should I begin timing from the push of the button? (I realize that many people don't even time their shots and that timing is much of the time a tool for newbies but I'm looking for recommendations here).

Thanks, any help you guys could offer on these questions would be really appreciated and relieve a little stress so that I can start enjoying my new machine. :D

eastbaysanfranman (original poster)
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#9: Post by eastbaysanfranman (original poster) »

Ok, ok, ok, before anybody says it, I clicked, for the first time, on the resources page. Here goes more, reading, reading, reading...

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HB
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#10: Post by HB »

1). Based on your previous post, I think you're flushing too much and allowing too long a rebound. Although I've never used an Oscar, based on what I've read, it's a Dragon. If so, a flush-n-go technique with rebound time of 10 seconds is a good starting point.

2a). Your method of laying a thermocouple across the puck works, though the type of thermometer you have may be slow to read (I use a Fluke 54-II and 36 gauge type T thermocouple for such measurements). That said, as someone who has a drawer full of temperature equipment, I recommend you spend more time tasting and less time measuring.

2b). See I still don't get it: Why adjust the OPV? and Zero cost adapter for portafilter pressure gauge. Short answer: If your espresso machine has an over-pressure valve, adjust it to 9 bar. If not, you can add it. But it's mostly about lower pressure ristrettos (i.e., at double espresso flow rates, the pressure works out to around 10 bar).

3). Search is your friend: Timing of extraction starts when? and When do you start to time the shot? and Timing a double shot and When do you start timing your shots? and When to start timing shots from naked portafilter? and What is the correct method for shot timing? and ...
Dan Kehn

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