jpender wrote:
This morning I pulled two shots as identically as I could. The first was with the Robot stone cold. The second I preheated it fully (piston, portafilter, basket, screen). I have a temperature sensor embedded in my Robot, dangling below the piston so that it is immersed in the water during the shot.

Since you have such a nice setup, would you be able to do similar analysis for my Robot routine? Which is a two step process regarding preheating:

• preheating the piston using a cup filled with hottest water I can get from the kitchen faucet while waiting for the kettle to boil (I hold the cup with my hand submerging the piston in the water for about 1-1.5 minute). This also warms up the cup which is used for the shot.

• Use overfill pour over technique when filling the basket with boiling water (about 3 seconds overflow)

I don't do anything else. Obviously the results should be somewhere in the middle of your graph, but I am curious if it actually comes closer to the top line, which will suggest that preheating PF and the basket could be a bit of an overkill. It would be very interesting to see the actual results if you can find the time and desire to do such test.

I had the same thought as jpender: brew temperature mattering is an established fact, why should the robot be any different? I have to admit though, I haven't made any organized attempt to do side by side tasting of preheated vs not. Generally, I decide whether I am going to preheat or not in advance based on the appearance of the beans, and I tend to stick with it for subsequent shots.

I can say that with the Cafe Lusso "Roma" blend (the Gran miscela carmo variant that includes robusta that was out a while back) I started out not preheating, because I generally don't bother preheating medium to dark roasts. I heard though that people were having good results with higher brew temp and decided to give it a try. This wasn't blind, or even side to side, but I switched to preheating, felt like it made a difference for the better (coffee was 'spicier' and generally more complex) and stuck with it for the rest of the bag.

So take that for whatever it's worth, in that particular instance I at least believed it mattered.

I was actually in preparation for such test when the OP posted the question. What a coincidence, I thought. I have medium roasted beans that I really like, with very profound baked apple notes, quite different from other beans I usually buy. So I decided to try no preheat and see if I can still detect the apple notes that I really like. Note that I preheat using my simplified approach described above. Comparing between this approach and no preheat at all, very subjectively, I felt that baked apple notes moved further on the background and the traditional espresso/dark chocolate bitterness (not sourness) moved upfront in the taste. It was still a very good shot, sweet and not sour, but I felt it was less clean than with the preheat. The difference was so vague that this is when I started asking myself if what I am experiencing is real or pure psychological and decided to post about it. One way or another, I think I have to continue to preheat to ensure maximum enjoyment. But at least my method is not that onerous.

By the way, my other reasons for preheating the piston are - cleaning the gasket from grounds to reduce wear and tear, potentially creating better seal with warm piston, warming up the cup, and simply occupying myself with something possibly useful while waiting for water to boil.

jpender wrote:Why? Is there something about microwave radiation that affects coffee adversely? Or are you objecting to the shot being heated up 2-3°C?

I don't know how microwaving can affect the flavor. Why not eliminate a step that may obscure results rather than give the coffee enough time to go to room temperature? I'm influenced in part by the noticeable changes in flavor when I roast coffee and apply heat in small increments. Microwaving is different, but it induces a penetrating heat.

BTW I agree with another one of your comments that preheating is a useful item in one's toolbox.

VoidedTea wrote:Since you have such a nice setup, would you be able to do similar analysis for my Robot routine? Which is a two step process regarding preheating:

• preheating the piston using a cup filled with hottest water I can get from the kitchen faucet while waiting for the kettle to boil (I hold the cup with my hand submerging the piston in the water for about 1-1.5 minute). This also warms up the cup which is used for the shot.

• Use overfill pour over technique when filling the basket with boiling water (about 3 seconds overflow)

Sure, I can try to replicate your method and record the temperature curve. It might help if you can tell me the temperature of the water in the cup and also how much water it is. If it's like my tap then it would be about 50°C. A cold cup would reduce that a few degrees.

I usually boil water in a cup in the microwave. But I have done tests where I have preheated the piston less. Based on those I would predict that your piston preheating method is probably not very effective. Piston preheat mainly reduces the rate of temperature decline and my guess is that preheated with 50°C water the decline will be not much better than if you did nothing. That's my best guess.

On the other hand, when I do a double pour or the overflow method you describe I typically see a starting temperature of 94-95°C. And with no piston preheat (or an ineffective preheat) the temperature drops to about 84°C after 35 seconds.

drgary wrote:I don't know how microwaving can affect the flavor. Why not eliminate a step that may obscure results rather than give the coffee enough time to go to room temperature? I'm influenced in part by the noticeable changes in flavor when I roast coffee and apply heat in small increments. Microwaving is different, but it induces a penetrating heat.

I don't know what a penetrating heat means in the case of a liquid. And this was 5 seconds of microwaving to raise the temperature from around 63°C to a little over 65°C. I pulled these shots into cold cups and then transferred them to secondary cold cups. So the shots were already cooled down when I doused each of them with 4X as much 95°C water. That must have heated up the coffee a lot more than the microwave did afterward.

I could have waited the 15-20 minutes or whatever for them to both go stone cold. Taste differences are probably more apparent as straight shots versus diluted anyway. Maybe I'll try that tomorrow. This morning I was too thirsty to wait.


By the way, those two long blacks were indistinguishable to my taste buds. The coffee was Paradise Espresso Nuevo: 18g in, 30g out. They call it "dark" but it's really medium/dark. Nonetheless, past experience has taught me that preheating doesn't work well with this blend. So I was surprised that the the two cups tasted identical. But it's hard to say anything definitive other than that sometimes preheating doesn't appear to make any difference, which I already knew. It doesn't disprove the opposite.


EDIT (28 May): I tried the same thing but with straight shots that were stone cold. They both tasted the same or very, very close.

John,

Your taste impression suggests to me that this particular coffee and roast needs a threshold temperature to extract differing flavors. That's useful to know when dialing in similar coffees. I also wonder whether there's a threshold for adopting additional preheating techniques to overpouring, but that's probably more of a subject for your temperature tests thread and may already be discussed there.

Another update and this time with reported at least medium roast beans. I was in Chicagoland past weekend visiting my parents for lunch and grocery. The traffic in Chicago proper and surrounding Cook County is certainly back to near pre-pandemic levels. So this meant I could not add stop for my preferred CHicago roaster for medium to dark roast. My elderly parents are not that patient to be in my car that long despite me serving as chauffeur:(

So I purchased this supposed dark roasted bean from "best cafe near me" google recommendation which was near parents' residence on way home. https://brewpointcoffee.com/collections ... ouse-blend I have no clue (and no mention in the URI) of bean origin. I have never tried this roast or roaster prior. I was told by barista is it like full city; though they follow other roasting scale that is Greek to me as I don't home roast.

TL/DR:
* There is minimal difference in taste (positive) with preheating Cafelat Robot piston & portafilter & professional basket.
* With preheating this Stargazer blend has predominant main flavor of >70% cacao chocolate with secondary flavors wood (? oak) flavor and tertiary flavor of brown sugar (or molasses; it is a subtle sugar taste).
* W/o preheating, these three flavors are still there but all slight more muted. There was effectively no acidity in either espresso. Aftertaste for both methods was good (nothing objectionable).
* Will have the home-barista experts/developed palates give their opinion on next meetup.

Methodology:
* To be clear my palate is not in same galaxy as senior home-barista members like "another_jim," "dominico" or other senior forum members I have met in person at Chicago-Milwaukee get-togethers. I am just a simpleton. For me it's Siskel & Ebert (both R.I.P.) Thumbs up or down.

* Two brews w/o any preheating and two brews with full preheating. No triangle testing as I hate cold espresso. So this is comparing tasting notes all done within 48 hours. I only have at most two doppio espressos/24 hours.

* When preheating, PF and professional basket in thick-glass bowl filled with just-off-rolling-boiling water for at least 3 minutes. And piston heated for 1.5 to 2 minutes with ceramic mug filled with just-off-rolling-boiling water. All brewed to 66% brew ratio (20.5 grams bean and 30.5% drink and ~ 1.25 to 1.5 fluid ounce).

Grinder: Helor 106 (original version with Mazzer 0186 burrs i.e. original Robur 71mm single phase conical burrs).

Water: rpavlis (100mg/litre of potassium bicarbonate)

Michael,

That's a great post that confirms John's idea that preheating is a very useful tool when dialing in a new coffee. Thank you for going into detail of what you tasted and with your method for getting there.

It's been my impression that medium roast and darker generally do not require preheating with the Robot. Sometimes it seems to improve the flavor but other times it has little effect or makes things worse.

Where preheating seems to have greater value is with lighter roasted coffees. That's probably the place to look first for easier-to-detect differences. I would try this myself but all my coffee at the moment is medium or darker, comfort blends.