My E61 mushroom was looking worse for wear. Machine is ~8 years old and 50% of chrome had worn off.
So when I saw the "Coffee Sensor E61 Flow Control" kit, with it's stainless steel mushroom, I snapped one up and fitted it.
Coffee's since then have declined in quality. They started on par with the old mushroom and I tried all sorts of flow profiles.
Today I took it off and re-fitted the old mushroom (after sand papering off the chrome and giving it a good clean and polish).
Flavour, I think, has improved.
Isn't making espresso such an art of non-obvious things making big differences?
There must be something in the material of the mushroom affecting shot quality if Rocket went to the trouble of making their E61 mushroom ceramic.
Do they still do this? Does anyone know why? What's the logic/science behind it?
Why do they chrome plate the inside of the E61 that you don't see? Why not just leave it as brass like all the other internal plumbing?
Anyone else find SS mushrooms to be worse than brass?

My only one wild guess is that the specific heat capacity is different for the different materials/metal and therefore might effect the temp during the shot and you'll have to adjust the temperature.

jevenator wrote:My only one wild guess is that the specific heat capacity is different for the different materials/metal and therefore might effect the temp during the shot and you'll have to adjust the temperature.

I should have added that my machine is an HX machine.
I did try a range of temps with the PID but shots were either too sour or too bitter. I couldn't reproduce the sweetness I'd once enjoyed.
Yes heat conductivity would seem to be the obvious reason but why when it's enclosed inside a brass E61 group head?

A really interesting post. Thank you for posting.I have a HX machine soon to be 'upgraded' to a Decent. Reading for background research I recall Decent saying somewhere that stainless steel is easier to control for group head temperature as it cools down more easily. Brass heats up and retains heat much more readily so that is a key difference. The issue of course is that you need flow control and temperature control that allows a mix of hot and cold water to adjust temperature at the group head by way of a feedback loop. On a HX machine you are limited usually because you have none of these. You don't have control over the bar pressure, you don't have flow control unless you have a volumetric which allows preinfusion but still, this means 9 bar preinfusion wait x seconds and then full 9 bar extraction. You don't have the ability to manipulate the temperature aside from the preset sensor. Obviously some higher level machines have variations on this, but the only one I know that has all of this is the Decent. I think they are looking at a stainless steel group head for a future version but longer time Decent owners might correct this if I am wrong. I have often pondered this very question. If anyone else can add to this I would be grateful and if they could contribute and correct any anomalies in my post if I have made, please do so with explanations.

A thought just occurred to me after reading @Dartiguan's post.
Perhaps the purpose of chrome on a surface that isn't seen and water flows around is to reflect heat?
The inside of the mushroom isn't chrome just the outside. Usually anything that reflects light also reflects heat.
I'd love to know why Rocket went with a ceramic mushroom. It seems a lot of trouble to go to so there must have been a good reason.

You can control the feedback loop on the HX by changing the size of the restrictor valve at the top of the HX outlet of the boiler.
Doing so changes the mix of hot water and cooler water forced by pumping into the group head (E61 in my case).
I have done this and had it perfect but now I seem to have undone all the good I had done.
Stripped out the restrictor last night to check it but all is fine there.
Hoping it rights itself after a couple of weeks since it took a couple of weeks to get to this state.

I'm really not sure why ceramic mushrooms were used in the Rocket (and I'm not sure they still are). I'd guess that part of the reason was that the chrome plating on brass mushrooms tends to corrode over time and the exposed brass then builds up scale. Ceramic mushrooms aren't subject to the same problems, but they have others. The first is that they a brittle and crack fairly easily during handling. They also have a different (much lower) thermal expansion coefficient than brass or other metals (like SS), which can put them under mechanical stress when mated to other metal parts subject to great temperature fluctuations. The different extraction tastes you note between the old chromed mushroom versus the new SS one may, as another poster said, be due to the greater heat capacity of brass compared to SS, but I'm surprised that would be a major issue after the entire E61 group is brought up to stable temperature. It could be that your group needs maintenance, including a thorough internal cleaning/descaling.

I bet I find 20 different settings on HX espresso machine to have greater effect on the coffee than material of the mushroom in the E61.
Mine mushroom also peeled off chrome, so I cleaned it off, polished and let it working. Not sure why the chrome was there. I am thinking possibly because the top of the screw is chromed, so when the part is processed in the chrome plating, it must be chromed completely.

I would not hesitate to use stainless mushroom, if needed. It will be as good as brass one.
Ceramic mushroom? Well, why not, but I would rather spend money on good coffee.

My only beef with the ceramic ones is that they crack or shatter. The brass and stainless ones are nearly indestructible.

Pressino wrote:It could be that your group needs maintenance, including a thorough internal cleaning/descaling.

Nope it 'aint scale. When I got my machine, 2nd hand, last year it was badly scaled inside.
I spent a lot of time stripping, soaking and cleaning it. Which is why the mushroom lost a lot of its chrome plating.
My own water is rain water collected from my large roof space that is triple filtered.
Slightly acidic but zero mineral content which is another issue on its own...

We noticed a metallic taste to our coffee at the weekend so I swapped back in the Coffee Sensor stainless steel flow control mushroom.
The original brass mushroom had a nasty metal taste so that was almost definitely the culprit.
Coffee's are ok now, not as great as they once were but it might be the beans after all. Need to work on my "dialing in" skills.

One thing I have noticed is that with the stainless steel mushroom fitted the group head takes an extra 5 mins to heat up to a temperature I like to begin using it at (Eric's themometer on the head 89<>91C).
So perhaps that's the reason Rocket went with the ceramic? Faster warm up time?
I'd love to source one and fit it just to compare...

petr0x wrote:I bet I find 20 different settings on HX espresso machine to have greater effect on the coffee than material of the mushroom in the E61.
Mine mushroom also peeled off chrome, so I cleaned it off, polished and let it working. Not sure why the chrome was there. I am thinking possibly because the top of the screw is chromed, so when the part is processed in the chrome plating, it must be chromed

It might be that brass can contain lead so the chrome-plated brass is good safe.

Until the chrome plating wears off. Which might be why you can't obtain a chrome-plated brass mushroom anymore. Manufacturers have been continually improving their products to be lead free. But I'm only speculating.