Aluminium Stockpots Going Black on the Inside

[Nick T]

Hi There, just trialling equipment prior to my first ever brew. Using a 32 litre aluminium stockpot (from Southern Hospitality) on a Bunnings triple ring burner (which is going back today as the outer ring does not burn!). I got it to the boil (only with a lid on), and afterwards I saw that the inside of the stockpot has gone black where it had been in contact with the water. I have googled this and it seems to be a relatively common ocurrence (an oxide forming), but do you need to do anything about it or just leave it there? Will it affect the flavour of the brew, or will it even form if I am boiling wort and not just water?

[denimglen]

Did that happen with straight water? High chlorine in your water or something maybe?

I'd try to get rid of it. I'd look at a mild acid to clean it, maybe a boil with some white vinegar.

The alu should build a 'protective oxide layer', this will stop any off flavours or reactions with mild acids. As long as you're not cleaning it shiny bright you will be fine.

[Nick T]

Thanks for the reply. Yes it was straight water, Christchurch tap water (comes from deep artesian bores, very clean) so no chlorine and very low on any other elements as well. Had a bit of a boil with white vinegar in the water today, has taken a small bit of the black off the bottom of the pot but not much else. Some of the posts on other sites seem to suggest that the black is is the protective oxide layer, and that it should be left in place, others suggest that you should condition your aluminium with heating prior to boilng in it. Unfortunately a 32 litre pot does not fit in a normal oven to do this!

I will give it a mild scrub and try a reboil tonight I think.

[denimglen]

Passive oxide layer should be a dull silver colour I believe.

Maybe give it a scrub down with a scotchbrite pad or similar and just put the smallest ring of your burner on and let it sit on that for a few seconds?

[James P]

I have a 30 year old aluminium pot that I use to boil CHCH tap water to sterilise some equipment. This pot is used for all my pickles etc, and has the black surface where the water was. It seems to have had no effect on my cooking! (And no my cooking wasn't bad to begin with! :) )