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I am setting together fittings and ball valves for my homebrewing equipment and corrosion protection and food safety of material is a key decision point.

Yet there is a noticable price difference between the inox 304 (cheaper) and inox 316 (more expensive) stainless steel. I seek in this question the information where the difference between the two is, in particular with wort.

The key points are:

  • will 304 suffer (i.e. corrode) from wort (assuming there is sort of salts chloride existing in the wort) ?
  • will the 304 type of stainless steel (in case of corrosion) release any toxic materials into the wort ?
  • can the price difference (i.e. that 304 is 1/2 as expensive as 316) be confirmed?

I have read this:

304 stainless steel has a high resistance to rust. It withstands corrosion from most oxidizing acids and is often used for kitchen and food applications. However, it is susceptible to corrosion from chloride solutions (notably saline environments with high amounts of sodium chloride). Chloride ions can create localized areas of corrosion, called "pitting," which can spread beneath protective chromium barriers to compromise internal structures. Solutions with as little as 25 ppm of sodium chloride can begin to have a corrosive effect. (source http://www.reliance-foundry.com/blog/304-vs-316-stainless-steel)

which tells that 304 is fine for non-chloride setups. In beer-brewing terms would that mean that I am fine with 304 if I brew (chloride-reduced, i.e. not a Gose). ?

  • "assuming there is sort of chloride existings in the wort" - why to assume that? – Mołot Nov 20 '16 at 0:40
  • I think this is BS. My tap water has way more than 25ppm of NaCl in it. If this was a real life occurrence my gear would have dissolved into nothing years ago. That aside, I have a 10 gallon plain 304 stainless pot that I used for years as an extract brewer and my start into all grain. It still looks as good as it did the day I bought it. – brewchez Nov 21 '16 at 14:19
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    @brewchez indeed, most stainless used in saline pools is 304 and subject to 3500ppm salt with no issues. Though I've seen lots of damage to stainless filter tanks and handrails from scratching and not repassified. – Evil Zymurgist Nov 21 '16 at 16:00
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304 should be good enough for anything you are brewing, the wort will not affect it. 316 which is also know as (Marine grade stainless[1]) has 2% molybdenum which makes it more corrosion resistant, especially to chlorides, but for anything you are brewing 304 will be fine.

When cleaning, if you are using strong caustics then rinsing and re-passivating with Phosphoric or Per-acetic, is important no matter what Stainless you go with. If you don't you will leach iron out into the wort and get an annoying metallic taste in your beer, as Caustic strips off the oxide layer that protects the stainless.

If using chloride solutions for sanitation, always wash thoroughly and rinse with a acidic solution to re-passivate.

Chlorides also strip off the oxide layer and attack the underlying steel. When stainless cools there for small nodes around sulphur compounds that draw the nickel out of the steel to them leaving susceptible regions that the Cl- ions can attack. The addition of molybdenum to 316 helps prevent/protect this and prevents pitting. Once pits form, corrosion promoting chemicals can sit in them and accelerate the process.

[1] https://en.wikipedia.org/wiki/Marine_grade_stainless

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for brewing purposes you should be just fine with 304 stainless steel. It's what most breweries use for their production purposes. 316 is more expensive due to the addition of molybdenum which helps prevent corrosion from caustic chemicals, acids, or highly concentrated saline. None of which should be involved with your brew process, hopefully.

You can learn more if you're interested from this explainer video by Sanitary Fittings: https://sanitaryfittings.us/choosing-304-316-stainless-steel

protected by Community Feb 24 at 15:58

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