A few times already I noticed that my coffee would suddenly turn bitter. Previously I would blame new coffee, dirty roaster's drum, saturated ion filter, brew temperature, dirty grouphead.

However, this time it could not be any of them. I was going through the same beans I roasted, the ion filter was re-generated just a week ago, the brew temperature was the same, grouphead was cleaned-back-flushed less than a week ago. Yet, yesterday it was a perfectly good cuppa, today, it has got bitter rancid. What could it be?

This time I unscrewed the mushroom, and lo and behold, some nasty staff was all over it:


Same thing was inside the group head. I tried a bit of this stuff, it did not have any bitter taste, it was just tasteless.

However, after scrubbing it off, and firing up the machine, the taste of coffee got to normal again - there was not a trace of that overwhelming bitterness. Nothing else changed.
Was this stuff saturating water in the group head, and re-acting with something in the coffee, giving it very unpleasant taste?

My guess is that the remaining (after charcoal filter) chlorine in water reacts with copper, and the resulting product accumulates and finally reaches the point when I can feel it in the cup. Interestingly that it has a trigger-like character, one day everything was OK, the next day it is bitter and unpleasant.


By the way, here is the same mushroom a year ago, when my machine was new:

You should have a baseline for your filtered water quality. Then you can tell what is off when it changes. Clearly your incoming water is scaling your machine and is too hard. When my coffee started tasting off I immediately tested my in kind water and realized it had changed significantly. What had happened was that the LADWP had changed its water source to the Colorado river and doubled the hardness and tds causing my small bestmax filter to die prematurely and stop softening the water. I had to switch to an RO plus a large bestmax to get it in line. But I knew what had happened because I had a baseline. My call to LADWP just confirmed why, not what.

Thanks for reporting back on that. It's good news that your bitter taste was fixed by cleaning the mushroom, although I'm at a loss to understand why. As Lacoffee suggested, perhaps your water utility made a change in a way that caused those deposits to start dissolving rather than precipitating, and that was enough to affect the taste.

tonythewonderful wrote:My guess is that the remaining (after charcoal filter) chlorine in water reacts with copper,

You probably should get a water report or analysis from your water utility. A charcoal filter will remove chlorine, but not chloride (perhaps that's what you meant to type). Chloride, especially in low alkalinity water would react as you say to produce those blue-green deposits. (Read rpavlis' posts like this one: 1977 La Pavoni Europiccola with green deposits/scale to learn more about that.)

Some charcoal filters, including Brita, have resins in them in addition to the charcoal that can make your water more acidic and reduce the alkalinity (buffer), If your water's initial alkalinity is not high these filters can exacerbate the problem of chloride or sulfate corrosion.

Thank you for your input guys.
I really liked what rpavlis said there:

homeburrero wrote:(Read rpavlis' posts like this one: 1977 La Pavoni Europiccola with green deposits/scale to learn more about that.)

If only I could figure out how to automatically add potassium bicarbonate to water? (since I have plumbed machine's water tank directly to filters)

unfortunately I do not have a proper baseline test of my water. I did try using the hardness (total and carbonate) and pH tests I bought in a pet store. They are too crude, and showed the same normal 7.0 pH and either hardness was less than 5 dKH/kGH for water before and after filters. I guess eventually I will order a proper test in a lab.

For now I can say that cleaning off the scale from the mushroom solved the problem of bitter coffee. I think what I try next time same thing happens, is to remove carefully the scale and save it in a cup, then make an espresso, divide it into two, and add to one of the cups a bit of that scale. If it turns bitter with the added scale, that will be it.

I suggest you give your water utility a call. In the US, the Portland City water system switches from the Bull Mountain reservoir, which is a water shed on the west side of the Cascades to wells in later summer. They change the amount of Chlorine they treat the water with significantly. My wife's skin is highly sensitive to this and had a few years of agony until we made a few phone calls and discovered the issue.

We had no idea why there was no issue until late summer. We blamed all kinds of things on the problem until we discovered the facts and installed a Chlorine filter.

Our water district in Idaho is vastly better in water quality & consistency.

OK, guys, here is an update.

1. Just one week after cleaning I replaced the mushroom completely, because a new stainless steel one (from ChrisCoffee just arrived).

Here are both mushrooms for comparison. That amount of scale is just one week after complete cleaning.




2. Although at that stage of scaling the coffee was still OK, I decided to take some further steps:

- ion filter was completely removed
- two more carbon filters were added. So, I now have 3 consecutive activated carbon filters without any ion-exchange. Just for a good measure.
- I decided to give a try the idea rpavlis shared in 1977 La Pavoni Europiccola with green deposits/scale

rpavlis wrote:I personally use, as I have stated many times, about 0.5 to 1.0 mMolar potassium bicarbonate. You can simply add from 250 to 500 milligrams of potassium bicarbonate to a 5 litre container. You can use sodium bicarbonate too, but I do not like doing that because it seems to create peculiar flavours because Na is very low in coffee beans. You would use less of it perhaps 150 to 300 mg in 5 litres. If you used such water the deposits would all go away and more would not form. The copper would develop a very impervious coat of CuO. There would never be a need to descale. Water composition would not change during a session from separation of bicarbonates in the boiler.

I bought some food grade potassium bicarbonate and add every evening about 50 mg of it into the water tank. I just dilute it in a small amount of water, and poor into the tank - very easy. This tiny amount does not change the taste of water coming out of the grouphead - I cannot detect anything by taste.
What will happen to the scale is yet to be seen. However, I can now confirm that potassium bicarbonate made my coffee remarkably better! The coffee has got very pleasant sweetness, I never tasted before. It has already been 10 days and I like this set up more and more

So, thank you Robert (rpavlis) for sharing such a wonderful idea!!!

Tony, I believe that Robert is making the mineral additions to extremely low TDS distilled waters, but if I understand correctly you've removed your water softening cartridge and are only using carbon filtration along with the mineral additions referenced above to your tap water. This will not prevent scale. When Robert mentions that his mixture will reduce existing scale, part of that is that the TDS of the distilled water plus mineral additions is lower than the scale in the machine and the scale should be dissolved. Using a higher TDS water with the mineral additions is not recommended.

I've been adding minerals to Reverse Osmosis water for quite a while and have had very good luck with this.

yakster wrote:Tony, I believe that Robert is making the mineral additions to extremely low TDS distilled waters,

ooops... Thank you, Chris.
I did not realise Robert was talking only about low TDS (distilled) water.

My set up right now does not include any ion exchange filters at all, I disconnected even the small tank-filter that came with the machine - only three carbon filters (like this one) one after another.

At this stage I do not have any tangible data like water analysis to explain my observations here. All I can say is that the quality of my coffee is now much higher, and I feel the difference in taste (I know, I cannot really prove it ) and love my espresso more than ever!

So, I think I will just stick with this set up (carbon filters + very low doses of KHCO3) until something happens that will make necessary to fiddle with the machine further.