potassium metabisulfite / campden tablets measuring confusion!

Hi Rick, Some info here

Lum

That is truly confusing :-(

Wow....thanks, Lum. Didn't find THAT article! Appreciate the link and the info!

Rick

Yes, it can be. if my post was confusing, I meant to say I like using the powder as opposed to the campden tablets - - easier to dissolve, but when a lot of info seems to talk about measuring in grams, and all i have is teaspoons or 1/4 or 1/8 tsp., then needed to know the conversion process!

Lum's link was helpful.

Thanks.

Be careful. That article has some mistakes. For instance if you try to use his equation in the example given as

(30-10 + 5 for guess work) mg/L total. (5 ) (3.785)( 25) / (1000)(0.57)0.83 grams

you will not get the 0.83 grams he indicates, you will get 674 grams which is a little much.

He is shooting for 30-10+5 mg/L so I take it that means 25 mg/L He then multiplies this by the number of liters which is 5 * 3.785. So far so good. then he multiplies this by 25. I do not know where that 25 comes from. Then he divides by 1000 to convert to grams and then multiplies by 0.57 for the percent. I think he meant to divide by 0.57. I think the equation should have been:

(30-10 + 5 for guess work) mg/L total. (5 ) (3.785) / [(1000)(0.57)] = 0.83 grams

I think the equation should be:

(grams to add) = [ mg./L total * gals of wine * 3.785 gal/L ] / [ 1000 mg/gram * 0.57 ]

Lumping the constants together this could be simplified to:

(grams to add) = [mg./L total * gals of wine * 0.00664

where

0.00664 = 3.785/(1000*0.57)

Ray

I have created some software that calculates sulphite additions. You can choose teaspoons as the measurement unit if you wish.

I have a downloadable version here:

And an online version here (requires Java):

Or you can create a personalized sulphite addition table here:

All are completely free.

Ray, I don't see anything wrong with Lum's formula. You want to add 25 ppm (25 mg/L) of SO2 to a 19 L carboy (5 x 3.785 L). So what qty of K2S2O5 (pot. meta.) do you have to add?

(0.025 g)/L (19 L) / 0.57 = 0.833 g or,

(25 mg/L) (1 g/1000 mg) (5 gal) (3.785 L/gal) / 0.57 = 0,830 g

How did you arrive at 674 grams?

Guy

I cheat; I consider:

1/8 teaspoon per 5 gal (US) to be 20 PPM. 1/4 teaspoon per 5 gal (US) to be 40 PPM.

Technically that is 10% low, but I figure there are enough variables that affect this such as age of the actual chemicals that measuring with a balance is just not worth the effort.

I use the spoons correctly; I over-fill and wipe them flat with the side of another spoon. It works for me. I'm not saying you shouldn't do the calculations, just that this is one of the areas where close has been good enough for me over the years.

Joe

Two words - Digital scale.

His example has two lines. These are:

(30-10 + 5 for guess work) mg/L total. (5 ) (3.785) ( 25) / (1000)(0.57)= 0.83 grams

I take it that the second line is a continuation of the first line. The first line gives 473.125, therefore the equation is (473.125)( 25) / (1000)(0.57)= 0.83 grams or (473.125)( 25) (0.57)= / (1000)0.83 grams

6.74 = 0.83 This is not true.

Maybe he meant to divide by both 1000 and 0.57 such that the equation should be written (473.125)( 25) / ((1000)(0.57))= 0.83 grams

then it gives

20.75 = 0.83

Again not true.

If there is another way to interpret the given equation, then maybe someone can show me as I just do not see it.

Ray

Ray's correct that the equation is wrong - looks like a typo from an omitted division sign. Instead of

(gallons of wine you have) (3.785) (ppm or mg/L of total SO2 you want to add)/(1000) (0.57)

the formula should read (division added before 0.57:

(gallons of wine you have) (3.785) (ppm or mg/L of total SO2 you want to add)/(1000) /(0.57)

This gives the 0.83 for the example cited. The interpretation is

(gals of wine) * (3.785) = litres of wine to treat litres if wine * ppm = mg of SO2 to add to get desired ppm mg / 1000 = g of SO2 to add g * 0.57 = g of potassium sulifte needed to get desired g of SO2

Pp

Hi Rick

Normal dose for powder is 1/4 tsp for 5 Gallons. Normal dose for Campden tablets is 1 per gallon. (5 for 5 gallons). With nothing more than this to go on, 1 tablet = 1/20 tsp powder. HTH

Frederick

GOOD THUMB RULE BEEN USING IT FOR YEARS.