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I have read that when mixed in water, sodium percarbonate gradually dissolves, leaving behind only water. However, I have recently come across this video which says that pre-used sodium percarbonate solution remains effective and can be used to clean/sanitise more equipment, as long as two days after initial use.

  1. Does sodium percarbonate really leave behind only water, or is there something else left in the water that means it can be re-used, as suggested in the linked video?
  2. When using sodium percarbonate, is it necessary to completely fill all vessels and leave them to soak, or can a smaller amount be used to rinse equipment? I would like to minimise water usage if at all possible.

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  1. Does sodium percarbonate really leave behind only water? No!

Sodium percarbonate rapidly dissolves in water and dissociates into sodium, carbonate and hydrogen peroxide. 1

So no- not just water. But it does break down into "safe" compounds.

  1. When using sodium percarbonate, is it necessary to completely fill all vessels and leave them to soak?

It depends on what you're trying to do. Sodium percarbonate is marketed pretty widely as everything from a cleaner to a one-step sanitizer. I've typically only ever used it as a cleaner. If you want to clean a really gunky dirty fermenter- you might need a soak. If you just want to clean the dust out of a carboy then a quick rinse probably suffices. When cleaning a 5 gallon carboy I usually half fill it- and roll it around on the floor for a while until it's had good contact.

If you're using it as a sanitizer, it probably needs more contact time than something like iodophor or starsan, the packaging should tell you that.

As most of us here at homebrewing are likely only casual chemists at best, you might want to ask chemistry if you have any serious chemical questions/concerns!

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  • Yikes! Hydrogen peroxide is left behind? Surely that isn't what we would deem a 'safe' compound? Thanks for the heads-up though – I'll go ask a follow-up question in the Chemistry forum. Commented May 26, 2022 at 9:22
  • Follow-up: I did ask this question on the Chemistry page and they pointed out that hydrogen peroxide is not left over eventually: what is left is sodium cations and carbonate. I guess I'll now just need to check whether there are any risks posed by these. chemistry.stackexchange.com/questions/165387/… Commented May 26, 2022 at 10:21
  • Hydrogen peroxide residue is harmless in small quantities as it breaks down into water and free oxygen. Sodium carbonate on the other hand is also known as soda ash or washing soda and can leave soapy flavors behind even in small quantities. Commented May 27, 2022 at 12:30
  • @FrankvanWensveen I wonder why that is considered safe for disposal then? Washing soda is highly alkaline..? Commented Jun 1, 2022 at 7:42
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    It is, but the quantity used in home brewing applications is small. Also, washing soda is not worse in terms of effluent than what comes out of your washing machine or dishwasher every day in considerably larger amounts. Commented Jun 2, 2022 at 10:00
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Note that sodium percarbonate is not all that stable and breaks down into sodium carbonate (a.k.a. washing soda) and free oxygen which escapes into the atmosphere. There is no way of knowing if the sanitizing agent still has its peroxide component. That means that pre-used sodium percarbonate may or may not be still effective. The only way to tell is by whether or not your batch of beer has gone off. Is that worth the risk? In my personal opinion it isn't.

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sodium percarbonate has no cleaning capability or hydrogen peroxide in it after 6-8 hours. Using any left over for further cleaning is pointless!

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