My 100 litre stainless steel fermenter has turned a strange colour at the bottom?

Berry454 · Dec 8, 2024

Have two of these Polsineli 100 litre stainless steel fermenters and they have served me well over the years. Brilliant bolt down lids, seal for an airlock and a very handy tap on the side.

Recently one of the fermenters have turned a very strange colour at the bottom. Almost like the stainless steel has turned translucent and developed a pattern at the bottom?

Just a bit concerned as I was about to throw a few MYO white wine kits in this tomorrow?

Nucbrewer · Dec 8, 2024

Have you tried an acid cleaner? Or some bar keepers friend?

MashBag · Dec 9, 2024

TFR / caustic will sort that. All I ever use on my Polsineli tanks.

From here that looks like some silicon spray. I know cos I get a bit carried away with it, and have seen similar.

MashBag · Dec 9, 2024

Vodka and a cloth would prolly also shift it. I leave my tanks with a splash of vodka in and seal them up. You know they are clean when you need them.

peterpiper · Dec 9, 2024

Nucbrewer said:
Have you tried an acid cleaner? Or some bar keepers friend?

2nd, Barkeepers Friend (an acidic cleaner).

I use it, on base of my AIO system, if it starts looking similar. But is only needed occasionally, maybe once, every 6 or so brews.
I prefer the powered version (a mild abrasive), to the cream.

Good alternative is citric acid (lemon juice) not strong hydrochloric/ sulphuric acids, which can etch SS.

Stainless steel 'passivation' (rejuvination), removes free iron from the surface of the metal, using an acid solution oxidant (typically citric or nitric), to prevent rust.

If you have hard water, it might be worth adding a splash of citric acid, to the final rinse water. I might start doing that myself, to make sure that Oxy-clean used for cleaning (which feels alkaline), has definately been neutralised.
I used to think that Sodium metabisulfite (Campdem tablet) solution would do that. But have just spotted, that it's a reducing agent and antioxidant. Rather than oxidant (that's wanted).

A friends SS immersion chiller started rusting in spots (I suspect it had been put away damp). Was cleaned with Bar Keepers Friend, over a year ago. No rust again - so far.

Alkiline 'Caustic' is the opposite of acidic!

MashBag · Dec 9, 2024

peterpiper said:
Alkiline 'Caustic' is the opposite of acidic!

I am speechless (and that is new

) What a lot of extra cost and chemicals and faff I don't have... Cos I use caustic TFR everytime. On all my stainless stuff.
It comes up clean, doesn't discolour and doesn't need further intervention.

Perhaps cleaning needs alkalinity and not acidity