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Old 07-12-2012, 04:01 PM   #1
bob1
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Default SO2 Potassium metabisulfite

No one seems to be the same on this 1/4 tsp of Potassium metabisulfite = ppm in 5 gal and in 6 gallon. I have seen it range from 30ppm - 75 ppm. I know its better to measure but I am not able to measure to .10 gram yet. I was just looking at a presentation on this site showing a 1/4 tsp = 19ppm in 6 gallons.

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Old 07-12-2012, 04:26 PM   #2
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I use a solution to keep from getting too anal about tenths of grams. I dissolve 2 tsp in 20oz of water. I use a syringe to add 15ml (1/2 oz) of the solution per gallon.

If you math this out, it's the same as 1/4 tsp in 5 gallons. 20oz of this solution usually lasts several weeks. I keep the solution in a Mason jar with a plastic lid. Don't use the metal lids ... the fumes eat the zinc coating.

By carefully measuring/mixing larger quantities like this, the per gallon variance is minimized.

My earlier additions are done by calendar. A racking or two before bottling I A/O and make more precise additions based on pH.

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Old 07-12-2012, 07:20 PM   #3
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yes I have been thinking it might be easier than using it in powder form but I still see so many differences in what is in a 1/4 tsp (1.4 grams) =19,25, 30,55,75 ppm. And from what I see 1/4 tsp for 5 gallons is to much if at a ph of 3.2. I may be mixing up the differences of additions at different ph levels 3.2 and 3.4 when reading the different chart additions. You think you have this stuff down then you run across things that send 4 or 5 different directions. See if I can explain
white wine ph 3.4 - needs a bound of .8 molecular in order to maintain this wee need an addition of 21 ppm. now if 1/4 tsp is 75 ppm so2 and only 55 ppm will remain free ,it is to much. Seems the addition should be closer to 1/8 tsp.

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Old 07-12-2012, 07:39 PM   #4
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http://brsquared.org/wine/Articles/SO2/SO2.htm is the best single paper I've seen on so2.

As far as ppm (mg/l) goes, it's straight forward to do the math. Kmeta is 57.6%. So there are 576mg/g, or 806.4mg in your 1.4g.

There are 18.93L in 5 gallons, so an addition of 806.4mg to 18.93L is 42.599mg/L, or 42.599ppm.

Do a little rounding and allow for less than nominal strength and call it 42. What the heck, maybe we didn't get exactly 1.4g in our 1/4tsp measure, so let's be conservative and call it 40 :-)

Earlier additions will bind more and quicker than later additions, and it's best to calculate your required addition based on pH, as you said.
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Old 07-13-2012, 06:58 AM   #5
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Bob's answer is interesting, in that my whole take on this is that your 1/4 teaspoon and my 1/4 teaspoon will be different.

If you REALLY want to be correct, a high quality gram scale and a guaranteed chemical analysis of the K-meta would be necessary and a high quality pH meter.

Its not really that important in the overall scheme of winemaking on a home level...

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Old 07-13-2012, 08:22 AM   #6
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we had bought a digital gr/oz/lb scale a while back and have found that it is real convenient for measuring weight of wine materials.

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Old 07-13-2012, 08:53 AM   #7
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Thanks good read. I either learned a ton or something else. I see now the charts I am looking at are free SO2. So with the assumption of 50% bound and 50% free and 1/4 tsp per 5 gallons = Conservatively 40 ppm total then this would be the bottom addition for a white at a ph of 3.2 (20 ppm). So it seems as if 1/4 tsp is about right for fruit wine racking but may be a little shy if macerating on fruit. The post is not really for accuracy but I had seen the SO2 addition charts and thought that I was using to much SO2 but I see you need to double them now.

Also most all bound SO2 is made with the must addition while sugar level is high but at end of fermentation all Free SO2 will be gone.

Did I learn anything here?

Buying the digital gram/oz/lb scale has been one of the best buys I have made and not just for wine and beer.

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Old 07-13-2012, 09:27 AM   #8
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You can spend a lot of time worrying about SO2 levels and proper amounts needed to protect your wine. A good micro scale can be purchased from places like Amazon for less than $15. You should also pick up a set of weights to check the accuracy at the same time. Weights will set you back another $10 or so. Well worth it IMHO. Unless you want to spend several hundreds of $$$ on a pH meter, and SO2 analyzer you are stuck with adding SO2 every 3-4 months. I have done enough tests with an A/O rig to know that you really only need to add 1/8 tsp every 3-4 months. I have taken many red kits up to bottling (6 mo bulk aging) with just the included package of Sulfite and checked them just before bottling them and found the SO2 levels to be just fine for the pH of the wine. Whites are of course more prone to oxidation (browning) and need extra care. I usually find my white wines need a slight top up dose just before bottling which is 1/8tsp on average. I usually bottle my whites at about 3-4 mo bulk aging.

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Old 07-13-2012, 09:51 AM   #9
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in my first thinking that is exactly what I was thinking that 1/8 tsp would be fine for racking. What really got me to looking at this is when I do smaller batches of wine and use campden tabs I seem to get a off flavor. I bottle at 9 months so thats 75 x 3 rackings plus first addition in must = total 300 ppm added to a gallon.

in that article this also threw me for a loop

Due to the binding of SO2 to fruit particulates, the required doses may in practice be 75-100 mg/l for unclarified must

75 * 3.8 * 5 = 425 ppm for 5 gallon

I also ran across this while studying in winemakers mag

Hold on there, tiger! If you've got a standard 0.44 gram Campden tablet and you're putting it in one gallon of wine, you're blasting it with 66 mg/L sulfur dioxide, which is quite a lot if you've already been adding a tablet each time you rack. It's no wonder your wine tasted a little off.

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Old 07-13-2012, 10:16 AM   #10
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No! You do NOT want 425ppm! You want 425mg total for the 5g batch

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