Cold nose and consistent temps

For generic information on making espresso alt.coffee, coffee geek, Sweet Maria's web site and many others excel at this tutorial level of information. However, if you've been there and done that but have specific questions and concerns about getting the best espresso on the S1/VII/Mini-VII/Dream/Dream T, post those topics here.
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AndyPanda
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Cold nose and consistent temps

Post by AndyPanda » Wed Jun 28, 2017 8:40 pm

I'm fairly new to the world of S1 but not new to espresso. I've been reading all the old posts - a bit surprised at how few new posts there are and wondering if anyone will even see this post I'm making :-? And I wasn't sure whether to post this topic under Modifications or Tips or some other section ... I finally decided to post it in this section since the point of it all is to get a really great shot consistently. (Please relocate if you think this fits somewhere else better)

Since working with the Mini VII, I've been a bit frustrated trying to get a consistent temp ... especially since the whole reason I purchased this machine was because of its reputation for consistent shot temp. What I was finding was that in order to get the group up to temp (cold nose) requires a whole lot of flushing - more than the typical 2x2oz that I was reading most people here use. I was finding I needed to flush about 4x2oz or even 6x2oz to get the group up to where I'd get the same temp on the first shot that I would get on the second and third shot. (and I have read at least one post where a user was saying his first shot is never as good as 2nd and 3rd - and I think this is why).

As an experiment, I mounted a K-type thermocouple probe into the group head. I used a very quick reading probe that was right in the water flow above the group (inserted into the hole where the mechanical pre-infusion device goes). I ran like that for a week or two and learned what I could about how warming flushes correlated to brew temp. With the TC right in the water flow, it read much hotter than the group while the water was flowing fast (say flushing into a cup) but when the water flow stopped (flushing into a blind basket) or slowed way down (pulling a shot) the temp reading would drop to the temp of the group. (this is because the very hot water from boiler was moving slowly enough for the cooler brass mass of the group to pull the temp down)

The K-Type probe was only a temporary thing (wires dangling about) but I learned a lot. So then I took an inexpensive Taylor instant read - and pulled the wire and bead out of the metal sheath (so it can read quicker without the metal mass of the skewer) and attached the bead directly to the group and the readout mounted just above the control buttons.

I find that the group cools down to read about 83C within a couple of minutes of pulling a shot. Then it takes 2x2oz flushes to get back up to 86C or 4x2oz to get it back up to 88C or 6x2oz to get up to 90C.

If you were making espresso for a group and pulling back to back shots (and did the 2x2oz flush before the first), at the end of the first shot the group will be reading 87C, end of second shot 88, end of third = 89C, end of fourth = 90c, end of fifth - 91C, end of sixth and it's up to 92C and that's where it will stay for subsequent shots until you allow it to sit for a few minutes.

In my testing, if I just want to pull one shot ... I find I either have to pull 6-8x2oz flushes OR I can just set the temp up 2 degrees higher and do the standard 2x2oz flush. But then I'd have to remember to set the temp back down if I'm going to pull several shots.

I've found having the thermometer to be extremely handy for getting consistent shots. It has me thinking of how I could modify the group head with a PID controlled heater just for the group itself ... but that's for another project, right now I'm pretty happy with the results using the thermometer so I can get the group warmed to the same temp I know works.
S1_Thermometer.jpg
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AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Tue Jul 04, 2017 4:47 pm

I just made a video to show the group head temp rise when pulling several shots in a row. The temp keeps rising and I've measured that the temp hitting the coffee rises as well. For me, 6 warming flushes is the magic number - but that's a lot of wasted time and water and energy to reheat the boiler so I plan to build a grouphead warmer that will hold the group up to temp without the flushes.

https://youtu.be/ip91LZV8nb4

AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Fri Jul 07, 2017 4:49 am

well I built my group head warmer and it works so well I am blown away :bom:

I don't have to do any warming flushes at all, and get perfect water temp right at the beginning of the shot all the way to the end of the shot. And whether doing back to back shots or waiting 20 minutes between shots, they all start and end at the same temp without any warming flushes. And I can do flushes (rinse the portafilter, warm the cup etc.) without any change in the group temp since the group temp is already up to the same 92c that it gets to after 7-8 back to back shots/flushes. :bounce:

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Lav
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Re: Cold nose and consistent temps

Post by Lav » Fri Jul 07, 2017 9:44 am

Can you post a picture of your group warmer?


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Steffen

| La Spaziale Vivaldi II + myTimer mod |​ Mazzer Major doserless + ArduDoser, Wilfa WSCG-2 | Aillio Bullet R1 on preorder | Brewster Smart Scale | ​AeroPress, Bialetti Venus |

AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Fri Jul 07, 2017 11:35 am

This is just the rough prototype, hand made from stuff I had lying about. I'll make a nicer one and seal it with hi temp silicone and route the wiring inside. Right now it is just wired to a power cord and plugged into a power strip so I can easily switch the power on and off as needed. But I'll probably put a PWM control to adjust the power so it idles at the right power. If I just leave it on full it will keep rising over 100c and I found the sweet spot is 92c.
HeaterOnGroup.jpg
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My mica heater is hand made by winding nichrome wire around a mica strip and then sandwiching between two wider mica strips so the windings aren't exposed. Here's a picture I drew and a photo of a commercially available mica heater just to give you the idea of what mine looks like inside.
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goodboyr
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Re: Cold nose and consistent temps

Post by goodboyr » Fri Jul 07, 2017 11:55 am

Lol. Cool, but just make sure your pf handle is well insulated......

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AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Fri Jul 07, 2017 12:06 pm

lol .... but seriously the portafilter (and the handle) only gets to the exact same temp that it would get to if you wasted half a tank of water pulling warming flushes or if you were making several espressos for dinner guests.

EDIT: Oh .. I finally realized that you probably meant "insulated electrically" - I thought you meant the handle would be hot. whoosh - went right over my head. lol I have heaps of electronics experience so of course I measured that the heater strip is electrically insulated inside a mica sandwich (mica is non-conductive and handles very high temps - that's why they use it for heaters and toasters etc.). But I do need to waterproof it with hi-temp silicone when the hardware store opens this morning.

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goodboyr
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Re: Cold nose and consistent temps

Post by goodboyr » Sat Jul 08, 2017 2:48 am



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Lav
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Re: Cold nose and consistent temps

Post by Lav » Sat Jul 08, 2017 2:49 am

Very cool - ehm... hot!
Thanks for posting all this information Andy It is so good to have someone like you on the forum that tingle with the mechanics to make it even better. A few years back I was more active, but I think I'll be copying this mod.


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| La Spaziale Vivaldi II + myTimer mod |​ Mazzer Major doserless + ArduDoser, Wilfa WSCG-2 | Aillio Bullet R1 on preorder | Brewster Smart Scale | ​AeroPress, Bialetti Venus |

AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Sat Jul 08, 2017 6:38 pm

Thought I'd update now that I've had a day to live with this and try a few things.

What I did at first was to simply turn the power on and wait about 60-80 seconds (that was enough time to warm the group from 82C up to 91C) and then turn the power off and pull as many shots as I wanted (the group would stay right around 90-92C depending on how fast you could prepare a basket and pull another shot). Then if I came back 5 minutes later, the group would have cooled down to 82C again so flip the power on for the group heater and 90 seconds later turn the power off (having the thermometer mounted makes it just easy as pie to see what's going on).

So next I hooked up a light dimmer to the heater - I found that set to 3/4 power would hold the temp pretty steady at 92C (but not perfectly - it would either be very slowly falling or very slowly rising). I also found that once I got it warmed to 92 and set so it held steady, if I then pulled a shot or flush, the group temp would creep up. The combination of the hotter water from the boiler plus the heat energy from the group warmer was enough to rise higher than you'd normally see just pulling back to back shots. I would see the group creep up to 95C and it may have gone higher. So the dimmer isn't really a good solution.

A PID would probably be a good solution but it seems like overkill. I'm surprised to find that the very primitive method of just flipping on the power for 90 seconds to get the group up to 91-92C and then turning it off and pulling your shots --- well that seems to work about perfectly for my routine. When I come back later, I just flip the power on and watch the thermometer and it's just easy and quicker than pulling warming flushes and waiting for the boiler to recover. By turning it off before I start pulling my shots I don't see any further creep in group temp, it just settles in and stays right at that temp until you stop pulling shots.

I haven't measured the wattage - but I've made some estimates based on the length of heater wire and gauge and DC resistance - and I think my heater is about 90 watts.

I got the raw materials for my heater from a very inexpensive Crock Pot "little dipper" (16oz, tiny crock pot). The heater strip is wrapped around the crock and is way too long. It has sheet metal crimped tightly around it and I removed the sheet metal to expose the mica strips and very fine RCH heater wire. I cut the mica strips to the length I wanted (very touchy stuff, the mica will crumble if you are rough) and attached the lead wires to the, now shorter, heater wire ends. You can order these in custom lengths but I'd expect you need to order 1000 of them.

Before I thought of robbing the heater from the crockpot (never had a use for the crock pot) I had planned to use a 100watt halogen bulb or a 100watt cartridge heater. And those may work as well or better - and you wouldn't have to fiddle around with the tiny gauge heater wire and fragile mica strips.

AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Mon Jul 10, 2017 4:38 pm

Just wanted to reiterate one of the things I wanted to try and accomplish with this mod. Of course I wanted to reduce the need for flushes - having the mini and refilling the tank being an issue for me. But much more than that, what I most wanted to achieve was to be able to have the shot temp start out hot rather than the typical profile the S1 gives where the shot starts out cool and then gradually gets hotter as the shot progresses.

Many espresso geeks are starting to want to see a starting temp of 202F dropping to 198F (sorry, I still think in F on brew temp) by end of shot for certain coffees - and this is the opposite temp profile that I was seeing from the S1 before modifying it. Now, with the grouphead heater, I am able to warm the grouphead up (say 94C) and set the boiler temp lower (say 92C - with no offset) and get a shot that starts out hot and gradually cools as the shot progresses. Or I can warm the grouphead to 88C (simulate the 2 warming flushes) and set the boiler to 93C with a +2 or +3 offset that most of us use - then I'd get the typical profile where the shot starts out around 196F and gets up to 200F by the end of the shot.

To my mind, the cool start and hot finish exaggerates the sour beginning and bitter end --- while the hot start and cooler finish tames the sour beginning and the bitter end.

AndyPanda
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Re: Cold nose and consistent temps

Post by AndyPanda » Mon Dec 11, 2017 2:08 pm

Just thought I'd check back in - still seems very quiet around here :-P

I have been using the machine for several months now and haven't made any changes to the mod. I found a spot on the dimmer controlling the group heater (about 3/4 power) where I simply turn on the espresso machine to warm up and flip the power switch for the group heater and then leave it alone to warm up (I do run the pump until water comes out the group just to make sure the boiler is topped up and pump is primed). If I come back in 5-10 minutes it's all ready to go --- if it's been 30 minutes then the group is a bit too hot, 98C, but all I need to do is pull the portafilter handle off and let it cool for a few seconds and then lock it back in and that pulls the group temp down where I want it. Or I can just turn off the group heater for 30 seconds.

This has really worked well for me. I love not having to constantly fill the water reservoir and I only do one, small flush just to warm up my cup.

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