# SO2 Potassium metabisulfite



## bob1

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.


----------



## BobF

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.


----------



## bob1

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.


----------



## BobF

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.


----------



## DoctorCAD

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...


----------



## tonyandkory

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.


----------



## bob1

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.


----------



## ibglowin

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.


----------



## bob1

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.*


----------



## BobF

No! You do NOT want 425ppm! You want 425mg total for the 5g batch


----------



## bob1

No! You do NOT want 425ppm! You want 425mg total for the 5g batch

thats right and there is 806.4mg in a 1/4 tsp.
correct? So they are saying 1/8 tsp


----------



## bob1

I see I can not use a calculater

*75 * 3.8 * 5 = 425 ppm for 5 gallon*

75*3.8*5=1425mg and a 1/4 tsp is 806.4mg so that addition is closer to 1/2 tsp


----------



## BobF

Let's backtrack just a bit.

There are different uses for kmeta. Initially, kmeta is used as a must additive to set back wild yeast and spoilage organisms for the purpose of giving your chosen yeast the opportunity to dominate the ferment and to prevent spoilage while the must is being turned into wine.

Post-ferment kmeta is used to preserve and to protect against oxidation. Post ferment requirements are different than must prep requirements.

Pre-ferment most use the standard addition of 1/4tsp unless the fruit/grapes have an abnormal degree of rot/mold/etc. Personally, I don't used less than sound fruit, but I guess sometimes there isn't a choice. Unless the condition of the fruit is suspect, I would stick 1/4tsp/5g. Regardless of the amount used pre-ferment, you want to keep some stuff in mind. First, by the end of the ferment, there will likely be zero free so2 remaining. However, there will be bound so2 which -could- inhibit MLF. If you're planning MLF, plan so2 additions accordingly ....

Second, if you do an extra large so2 must addition, make sure you give the appropriate time prior to pitching yeast. While commercial yeasts are more/less so2 tolerant in general, high doses can lead to stressed yeast, which frequently manifests itself as h2s.

Really, I would keep it simple. Use sound fruit, normal so2 additions, good sanitary practices and sound methodology. Don't fret the decimal points and enjoy your winemaking experience. Wait until later to plunge into the deep end of the nit pool - the tickets are expensive and demanding on one's time.


----------



## bob1

yes I agree and to want to get a hold of the decimal place and put it behind me. Just as I may forget all of this it will be back there somewhere telling me I know what I am doing and want to keep a simple standard addition afterwards. But I have learned the camden tabs were a mistake.

5- 6 gal

After saying that It seems 1/4 tsp over crushed fruit at beginning will help set the bound SO2 , all free will then be gone and then 1/8 tsp is all that is needed after fermentation and every racking. 

I guess if I have this right the above should maintain about 30 ppm free in the wine and have a total of 100 ppm total for the wine.

Yes I remember reading the problems of to much SO2 in must .So not accounting for losses 44 ppm yield 20 ppm just enough to guarantee that I have shut down MLF.


----------



## BobF

An approach that works well for many is to use 1/4tsp post-ferment, then 1/4tsp every 3mos or so. I time my bottling for a month after the last so2 addition/racking.


----------



## bob1

No addition is made at bottling?


----------



## BobF

Not if my last addition was within a month, which I plan it to be. As Julie pointed out in another thread, there can sometimes be a light sediment thrown off with a sulfite addition. I give mine the month, carefully rack and bottle from the there.


----------



## bob1

Thanks Bob I feel like I learned a ton today. Appreciate the help with the math your right it is straight forward but sometimes parts of an equation when written in words just dont seem the same or just dont jump out at you.


----------



## ibglowin

Well done BobF!


----------



## BobF

You're welcome, bob. Feel free to ask more questions along the way as you reach specific milestones. There are tons of knowledgeable, experienced folks here that are eager to help. I learn from them every day  

Winemaking is a journey with rewards far beyond what ends up in our favorite glass. Really


----------



## dangerdave

Good info, Bob. Your advice "Don't fret the decimal points and enjoy your winemaking experience." is spot on! I think of winemaking like cooking. I love to cook, as well. I have recipes where I never use a measuring cup or spoon. That being said, please measure your ingredients for your wine with care, but don't fret. It's supposed to be fun, not stressful!


----------

