SO2

That's a big question, but you failed to mention the most important form of sulfur in wine: _molecular_ free SO2.

To adequately protect wine from microbial spoilage, as well as the effects of oxygen, wine needs to be maintained at 0.8 ppm molecular free SO2. That's actually SO2 in the gaseous state, dissolved in the wine. The level

0.8 ppm was arrived at because it is just sufficient to inhibit spoilage, while remaining below the normal sensory threshold.

You achieve 0.8 ppm molecular free SO2 by adding sulfite to the wine. How _much_ sulfite you need to add depends on two things: (1) how much sulfite is already present, and (2) the pH of the wine.

For a typical wine at pH 3.50, you need to have about 50 ppm free SO2 to achieve 0.8 ppm molecular SO2. If the pH were 3.20, you'd only need about

20 ppm free. If the pH were 3.80, you'd need closer to 80 ppm free. If you'll notice, the digits to the right of the decimal of the pH measurement are the same as the target free SO2. That's only a rough approximation, but it's pretty close.

When you run a Ripper test on your wine, the result you get is free SO2. From that and the pH you can calculate how much potassium metabisulfite you need to add to your wine to get it to where it needs to be. For example, your wine is at pH 3.5, and the free SO2 is 20 ppm. You should add 30 ppm sulfite to bring the wine to 50 ppm free.

The last item is total SO2. That's simply the sum of the free SO2 and SO2 that's been permanently bound within the wine such that it isn't available to protect the wine. If you add sulfite to freshly crushed juice or must, part or all of it will bond with aldehydes and other things in the juice. Once those bonding sites are all saturated, any additional sulfite added simply raises the free SO2. A typical scenario is white juice at 3.50 pH. If you add 50 ppm SO2 and measure the free SO2 in a couple of days, much of the addition will not show up in the reading because it has been bound. You can measure the total SO2 in a wine by chemically releasing the bound portion, but that's not really necessary for most purposes. You just need to be aware of the phenomenon so you are not taken by surprise when your first sulfite addition inexplicably "disappears".

I hope that's clear. You might need to read it a couple of times to get it straight in your mind, and I didn't go into any great depth with dissociation constants and all that incomprehensible muck. For more detailed info you should get a good winemaking textbook, but you really don't need that for practical winemaking. A feel for the way things work is sufficient. You can always ask questions if you don't understand something.

Tom S

Hi Tom S

Thank you so much. This is the best explanati> "To adequately protect wine from microbial spoilage, as well as the

While lesser levels will provide an anti-oxidant effect, the MINIMUM level to protect against microbial spoilage is 0.8 ppm molecular. This is what "aseptic level" means.

You can't be just a little bit pregnant. Either you is or you ain't !! And you can't be just a little bit "aseptic" !! Either you is or you ain't !!

FWIW - I prefer to use a minimum level of 0.83 ppm molecular because this level also covers "bret" and many of the "wild" yeasts that may be encountered. (but that's evidently just me) HTH

Best regards Frederick

inhibit

threshold."........

frederick ploegman wrote:

It should be remembered that these values are notional. There is no ultimate minimum level that is 100% safe in terms of protection. The value of 0.8 mg/l molecular was arrived at because of a landmark study by Beech et al. (1979) which found that 0.825 mg/l was required to reduce non-growing yeast and bacterial (included Brett and LAB) populations by 10,000 viable cells/ml over a 24 hour period in 10% ethanol buffered solutions. However, the strains of Zygosaccharomayces bailii and Lactobacillus plantarum required 1.50 mg/l and 4 mg/l respectively.

Different strains will be resistant to different levels. Additionally, these values do not account for the fact that strains can build-up resistance to SO2. It should therefore be remembered that the 0.8 figure is an estimated notional value. It *does not* mean your wine will most definitely be protected from LAB or Brett if you use this level, however it is a level which will protect against a number of strains successfully. Ben

Improved Winemaking

Tom

Perhaps access to two graphs/charts in Margolit's book for small wineries would also be helpful. Reference to these charts requires only a knowledge of the pH, and a look at the chart(s) to know how much sulfite to add to bring a given wine to between 0.5 and 0.8 ppm of molecular free SO2. I keep them taped to the wall of the winery for quick reference. They have certainly helped me.

Regards

Jerry

Too bad this isn't a binary newsgroup or you could have posted them - although there might be copyright issues if you had. :^(

Tom S

Hi Ben

All this considered, what level do you_personally_use in your own day to day winemaking ??

Frederick

It depends on the wine, but it would usually be in the 0.6-2 mg/l range.

BTW, I don't see my original post here - but obviously others can ?? I really dislike this Google beta version!

Ben

It depends on the wine, but it would usually be in the 0.6-2 mg/l range.

BTW, I don't see my original post here - but obviously others can ?? I really dislike this Google beta version!

Ben

Hi Tom S

Ben has a similar chart on his site. Can't seem to find my "link" list this morning but if you look on his "SO2" page you will find it. HTH

Frederick