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FAQ || 14 Gallon Stainless Brew Kettle

Q: I’ve had some trouble with a metallic taste in my beers. I use a stainless steel keg converted to a brew kettle. It’s very nice, but I find I have to scrub the stuffing out of it to get rid of all the baked-on crud. Could this be causing the problem?


A: Yes it could. If you’ve been following the articles about stainless steel in BrewingTechniques recently (2–4), you know that what makes stainless steel stainless is a layer of tough oxides on the surface. That layer can be removed if you abrade the surface enough — for example, by bearing down with a metal scouring pad or a wire brush. If you strip off the oxide layer, what is underneath is mostly steel, which is mostly iron, and this iron could get into your wort and give it a metallic taste.

I suggest soaking your kettle for a while using TSP or a metasilicate-based cleaner. Scrub it only with a nonmetal kitchen scrub pad. That method should enable you to get it clean. It will not, however, restore the oxide layer.

To restore the oxide layer (see reference 2 for a discussion of passivation), you will have to recondition the stainless with an acid. I suggest using a high-foam phosphoric acid–based cleaner. Scrub the kettle well with this solution — don’t forget to wear rubber gloves — and then let the foam stand in contact with the metal. After 10 minutes whip up the foam again and scrub some more. Repeat this four more times, for a total contact time of one hour.

I suggest repeating this acid treatment after your next three or four brews; then you can go back to a shorter cleaning regimen. It would be a good idea, however, to use a short acid treatment periodically on the kettle following the alkaline cleaner. You need not do this every brew, but doing it every third or fourth brew will help keep your stainless in good shape.