Sorry need clarification on campden (metric)

[BikerMatt]

I know this subject has been beaten to death and I have searched thoroughly yet I still have two questions on which I need specification.

ONE: They don`t sell Campden tablets in Finland YET I did manage to get a hold of 10gram pouches of Campden brand potassium metabisulfite. I usually brew around 20L/5gal per batch. One tablet, depending on source seems to weigh 0.4-0.65grams, and to dechlorinate 20L of water I need half a tablet, so let`s say 1/3 of a gram. ten tablets make an even teaspoon so one tablet is 1/10th, therefore half a tablet is 1/20th of a teaspoon right? So without buying a microscale the answer is "a pinch"? a tip of a teaspoon? The reason I`m asking is there was a water mainline burst some time ago here of which I found out only AFTER I brewed two nights in a row so I now have two ruined batches of beer that taste like licking a salvequick plaster.

TWO: and this is the one I haven`t really found a definitive answer to. WHEN to add the powder? Right into the cold strike water? Cause some sources say the effect is immadiate while others clim it takes 24h to take effect which baffles me. I have a 45L electric brewmonk with a circulating pump so I`d assume if I pitch the powder into the cold water the pump would take care of mixing it up thoroughly enough before reaching temperature right?

TIA

 

[Witherby]

This thread should have everything you need: https://www.homebrewtalk.com/threads/campden-tablets-sulfites-and-brewing-water.361073/

I would advise against just guessing the amount. I have excellent soft water but my town uses chlorine and chloramine so I always add potassium metabisufite to my brewing water as I am bringing it up to mash temp. The reaction is instant. I use Bru’nwater to determine the amount and a scale the goes to hundredths of a gram.

This summer I got the bright idea to start adding potassium metabisufite to the water I brew my coffee with. I would add a tiny bit to a 3 liter jar we have.

Fast forward a few weeks later and I think I have a stomach bug. And for the next month I have very loose bowel movements all the time. I was about to go to the doctor and was wondering if anything had changed in my diet since I knew the doctor would ask me. Then I realized the only change was the coffee water! I immediately stopped using it and within a day or two I was back to normal.

Long story short, a pinch is less than you think it is! It is not worth the risk of guessing. There are cheap pocket scales. They are worth it.

 

[BikerMatt]

Thanks for this, I did eye up that thread last night but was still a bit unsure. So as a sum-up, about 0.3grams per 20L, added into warming up strike water. I did some googling and managed to find a Bergen brand jeweler's scale that goes to 0.1g for 13,90 home delivered and ordered one, here's hoping it will arrive by Friday.