SO2

I believe it is 57% of the weight of the K-meta will be SO2. Campden has other "inert" binders added to it to hold the tablet shape, so it has more other stuff per gram than pure K-meta. Also, Isn't campden tablets sodium-meta and not K-meta ?

K-meta is about 58% SO2.

Campden tablets are designed to have about 0.44 grams of (often K-) meta. Whether they are 48% SO2 or not really depends on the tablet size, which tends to vary depending on the manufacturing process.

It means you'll get ~58% *total* SO2. Some of that will then become free, and some will become bound (total = bound + free).

See

Ben

And FWIW, when I've "standardized" bags of meta, I've found actual levels more like 36%.

And it'd be less if you use hot water or water with chlorine (so I've been told--does anyone know for sure if chlorine reacts with SO2) to dissolve your meta.

Dave

Greg, you can find campden in the form of k-meta too.

Ben, here a quote from the winemakermag :

"The key question now is: How much free SO2 is really added for any given amount of sulfite? Potassium metabisulfite and Campden tablets consist of approximately 57 percent and 48 percent SO2, respectively. This means that roughly half of the sulfite actually becomes free SO2 when a solution is prepared and added to wine."

Thanks for your link, I had already read it and many more about SO2 but I read different things about the 57% explanation. That's the only part i can't be sure of.

Séb

Hi,

It's easy enough to calculate for yourself. Meta is just K2S2O5, and the molecular weights of K, S, and O are 39, 32, and 16, repsectively. Find the total weight, and divide it into the weight of the 2 SO2 molecules you get from each meta molecule.

Voila! 57%.

:-)

Dave

Man has been adding sulfur dioxide to wine for more than a thousand years. A large body of knowledge exists on the use of sulfur dioxide in wine and in many other food products. The benefits of using sulfur dioxide are well documented, and its positive effects are indisputable.

I think your reference to time may be somewhat exaggerated. It's positive effects are also relative to what you want to obtain. For most home-made wine makers you will find that they generally do not store their wines for more than 3-4 years. They keep it stored usually under constant conditions and in a fairly cool cellar (10 - 15 C). And they are fairly hygienic in the way they work with the must and wine (compared to commercial production).

There is a minimum of risk w.r.t. spoiling the wine under such circumstances. The SO2 mania is something which have caught on by home wine makers, not because of an experienced problem, but rather because there is a belief that they need to take on all the practices of commercial wineries.

David C Breeden wrote "Ben-And FWIW, when I've "standardized" bags of meta, I've found actual levels more like 36%. And it'd be less if you use hot water or water with chlorine (so I've been told--does anyone know for sure if chlorine reacts with SO2) to dissolve your meta."

David and others interested in SO2 reactions. Here is an excerpt from an article on the subject. A.J.DeLange is a well known scientist in beer brewing circles. A lot of beer makers use K Meta to rid local water of chlorine and chloramine.

bill frazier olathe, kansas usa

Date: Tue, 08 Apr 2003 14:25:19 +0000From: "A.J. deLange" Subject: Chloramine/ZincFor Doug: The reaction between chlorine and bisulfite is:S2O5-2 + 4Cl + 3H2O --> 2SO4-2 + 6H+ + 4 Cl-With mono chloramine it is:S2O5-2 + 2H2NCl + 3H2O --> 2SO4-2 + 2H+ + 2Cl- + 2NH4+In either case the bisulfite is oxidized to sulfate and the clorine, while it is not "removed", is reduced to chloride ion.This method of removing chlorine has been used by aquarists for years (though they use thiosulfate rather than bisulfite). With the advent of chloramine they must be sure to have an effective means of removing the ammonium ion/ammonia that is produced. It's a simple thing to check out. Draw a glass of stinky chlorinated or chloraminated water and drop in the corner of a Campden tablet. The chlorine smell will be gone very quickly (to be replaced, perhaps, with a sulfur dioxide smell so only use the tiniest bit of the tablet - one tablet should treat 40 gallons of water containing 3 mg/L chloramine.

David C Breeden wrote "And FWIW, when I've "standardized" bags of meta, I've found actual

David and others...I'm sure you know that K Meta degrades rather significantly over a years time. I buy fresh every year because of this...it's inexpensive and you have a better chance of adding the correct amount of SO2.

bill frazier olathe, kansas usa

If you read the section titled "3. Sodium and Potassium Salts" you'll see why K meta is quoted as 57% SO2. Potassium metabisulphite has the chemical formula K2S2O5 and a molecular weight of 222.4, and sulphur dioxide has the chemical formula SO2 and a molecular weight of 64.1. Each mole of the potassium meta salt will give 2 moles of SO2, thus the SO2 content of K meta is 2 x 64.1/222.4 = 57.6%.

This, of course, is the theoretical maximum SO2 yield from K meta. In practise, it can be lower as Dave has mentioned.

Dave: I've had similar experiences as you have with the strength of my meta. It just depends on the supplier (i.e. how it's been stored, etc). These days I always check my SO2 stock solutions to make sure they're up to strength.

Ben

That's exactly right. But that would be TOTAL SO2 - not free SO2. Some will still be bound as sulfite. The free SO2 will be dependant on the pH of the wine. So I guess 57% would be more like a "potential" SO2 rather than the actual free SO2 in solution.

Not quite either of A or B, but B is closer.

BTW, forget about Campden tablets if you do any serious amount of winemaking. Buy meta in bulk and weigh it out yourself. You need a balance with an accuracy of 0.1 g or better. You also need to reseal the meta really well or it'll go dead on you.

K2S2O5 - straight out of a bag from the manufacturer - usually assays ~50%, ±2% available SO2. The stuff is very reactive to air - especially moist air. By the time you get it the assay will be ~50% if you got a good batch. Remember that part where I said to reseal the meta really well? I meant it. Solutions don't last too long either. Make fresh if you're adding it to your wine.

If you use this in a wine that has not been previously sulfited the free SO2 when you're done will be as if you used stuff that was only ~25%. A portion of the sulfite becomes _bound_ in the wine.

Once the requirement for bound sulfite has been met, whatever you add beyond that adds directly to the free SO2. That makes late adjustments really easy - assuming you know the pH (which is what determines your target free SO2).

This topic is not easy to grasp in its entirety, but it's very important to know about the 0.8 ppm molecular free SO2 requirement and its interrelation with pH and free SO2.

Tom S

snipped-for-privacy@lightlink.com

It is only a measure of the chemical content of the medium. It is your known starting point. As they say, "Settling may occur during shipment." and the old standby, "Your results may vary." :-)

Dad has been making wine for thirty plus years, and I don't think he even knows what SO2 is, or cares.

Fred

Depends on what your solution is. :-)

In water, it's really (theoretically) 57%.

But yeah, the figure I gave was just the theoretical chemical yield.

Dave

Thanks, Bill! That's really very useful!

Dave

William Frazier ( snipped-for-privacy@worldnet.att.net) wrote:

-- Dave