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F1 wrote:I have had this never ending problem with early blonding + bad flavor with every coffee for YEARS. I have tried everything at this point. Super Jolly, Compak K10, K30 Vario, WDT, no WDT, Pullman Chisel. My Profitec Pro 700 absolutely sucks and for some reason my Rocket Giotto works.
I have ran out of settings to try on the PID with the Pro 700. I have installed Eric's thermometer a while back. I also have a SCACE which should eliminate the need to even consider using Eric's thermometer, but I am actually a lot more confused if I use both at the same time.
When running the SCACE at the 20sec mark the SCACE shows 200F and Eric's shows between 206F to 207F and stays there pretty much flat for the duration of the shot. That's fine I know Eric's is supposed to show several degrees higher than actual puck temperature. As the shot progresses the SCACE very slowly climbs 200.1, 200.2, 200.3 and so on until the end of the simulated shot. By the end of the shot the SCACE shows a max of maybe 201F. This is all normal behavior so I am not worried about that.
The issue is when I run a portafilter with coffee. Obviously I can't use the SCACE so I look at Eric's thermometer. You would think it should behave the same, but it doesn't. As soon as I start the shot Eric's thermometer the first few seconds are the same as with the SCACE. Eric's thermometer climbs to 207F and stays there for maybe 2 seconds, then it starts dropping rapidly and by the 20 sec mark it is at 202F and at 25sec it is at 197F. This means that in the puck the temperature is around 200F for the first few seconds and by the end of the extraction it is around 190F. This would explain why every single coffee I make with the Pro 700 blonds so fast and tastes underextracted, but when made with the Rocket Giotto they dont.
Eric's device and mine don't measure the same thing. Eric's device is measuring water inside the group at the precise position of his thermometer, and mine measures water exiting the shower screen at the precise position of the thermometer. Eric's number is higher than mine because energy (heat) is lost between Eric's measuring point and mine. And Eric's measuring point is sensitive to thermosyphon action, which is somewhat complicated at times. It's pretty simple when the machine is idle. Less dense, relatively hotter water leaves the heat exchanger from the top, enters the group from the top, cools in the group, and becomes more dense. The denser water exits the group through the bottom pipe and flows back to the bottom of the hx. This convection cycle is the so-called thermosyphon action. Things change when brewing is activated. Thermosyphon stops and now water enters the group from both the bottom and top of the hx, with the proportion from top and bottom dependent on the respective flow resistances of the top and bottom flow paths. Scace devices employ a simplified flow scheme - a nozzle. So flow rate during brewing remains constant at approximately 55 gm/30 seconds at 9 bars of pressure. This value is nominally comensurate with 18 gms of coffee producing a brew ratio of 50%, assuming the dry coffee absorbs its weight in water (a pretty good assumption). But the constant flow rate idea is not what actually occurs in real brewing. Dry coffee has much less resistance to water flow than wet coffee. It aggressively absorbs water, is as full as possible of dissolvable solids, and it swells up as it absorbs water. Consequently the flow rate of water is very high in the first couple of seconds, and drops way down as soon as the coffee has absorbed all of the water that it can. What you see in Eric's device (the difference in behavior of Eric's device when measuring during real brewing vs. measuring against a Scace) is the thermal response to this big flow pulse at the beginning. In practice it doesn't matter by the time the water flows through the group as the temperature gets attenuated by the internal components of the group and energy loss to the surroundings.
There are no leaks on the machine and all the internal seals have been changed even though it shows no temperature drop with the SCACE. Most of the coffees I make at home I have tried at coffee shops so I know how they are supposed to taste. With the Giotto I can replicate this coffees at home, but not with the Pro 700. I don't get it. Any help?
Here are a couple of suggestions and ideas. Use VST baskets. Temperature and pressure are only part of the story. If the flow field through the coffee is preferentially through only part of the coffee bed, then you will overextract that portion and underextract the rest. Use of VST baskets ensures that you do not preferentially extract only a portion of the coffee. Use Vince Fedele's coffee refractometer to measure extraction yield if you can. You should be able to get extraction yields of around 18-20% at 50% brew ratio (ratio of dry coffee to beverage weight). Weigh coffee dose, final beverage weight, measure extraction time required to get the brew ratio you like (I prefer 55% as a starting point). Write down the extraction times and observe their variation. If you are controlling dose and beverage weight, then you should see extraction time consistency on the order of 2 seconds. Differences mean that you are channeling, and overextraction occurs at the channnels while underextraction occurs everywhere else. E-61 style grouups are really tolerant due to their slow pressure ramp. Non-e-61 groups channel more easily if there is not a means for slowing pressure rise sufficiently - so-called soft preinfusiion systems or manual preinfusion like on paddle group Marzoccos. Reduction of brewing pressure may help you with microchanneling and you will know because your extraction times will get more consistent and taste will improve.