MedPretzel
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- Aug 12, 2004
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A response I got in an email... This is the question I asked:
I've been thinking about it for a while (and I even bought a sulfite titrette kit, but don't really know what to do with it.).
I feel a little silly admitting that and asking this question, but....
Why would you need to know the sulfite levels other than if you are wondering over a stuck fermentation? Or am I missing something big here?
And this is the response I got:
I hope this can help others too.
I've been thinking about it for a while (and I even bought a sulfite titrette kit, but don't really know what to do with it.).
I feel a little silly admitting that and asking this question, but....
Why would you need to know the sulfite levels other than if you are wondering over a stuck fermentation? Or am I missing something big here?
And this is the response I got:
Martina, I think that sulphite are the most important aspect of winemaking. If you work with kits, this is easy because you only have to follow the instruction and add the sulphite package when requested. The calculation for the proper amount of sulphite has been made by the manufacturer. However, if you do work with fruits or grapes you have to add the proper quantity of sulphite for many important reason.
First, too much sulphite or too low can be dramatic and could ruin the whole batch. This is rare but it happen ( mainly when too low SO2 content ). In low sulphite wine, you will get a beautiful place for bacteria infection, including aceto vinegar which will turn your wine in a highly priced vinegarIn low sulphite wine, the color will be less bright, less attractive, oxydation will begin soon. In high content sulphite, you will get bad off-flavors, bad taste, a loose of the color intensity and in very large quantity it can be dangerous for your health ( but you know this better than me) .
You have to know that sulphite ( So2 ) is pH dependant. Meaning that the same amount add to a given wine will give different level of So2 concentration is the wine depending on the pH. Low pH wine required less quantity of sulphite for the same effect. In high pH wine you will required much more quantity of sulphite to get the same concentration in the wine. A low pH wine is below 3,45 and a high pH is more than 3,65. In between are the normal correct range for wines. Sulphite come in many sources. Most homewinemakers use potassium metabisulphite or sodium metabisulphite. Both salt have the same property but metabisulphite is better because it does not add sodium in the wine. Potassium metabisulphite is often refer to K-meta. When you add any given amount of k-meta to a wine, you will get some of this addition that will bound to some of the wine's components and O2 molecule and it is called fixed or bound So2. The remaining part that is not bound will remain as free state, therefore naming free So2. The free So2 is the one that protect the wine against microbial spoilage and oxydation. The quantity that are bound and stay free are not calculable with math. formulation. We can only estimate as this vary from wine to wine depending on the pH of the wine and the oxygen present in the wine and such. What is sure, is when you add the first dose of k-meta in a wine most of it will become bound and when the wine are at a certain level of bound So2, every further addition will stay mostly as free So2. However, every time the wine is expose to oxygen this will consume some of the free So2. That is why we need to add back k-meta if the wine is to be rack, filter, bottle, age for a while and such. Since we do not want a low So2 content in our wine and either a high concentration we need to know what are the free So2 level in our wine before doing anything. When we know that we have 20 ppm of free So2, we can estimate with formulation what amount will be required to get back to a more acceptable level or maybe 40-50 ppm.
We know So2 is pH dependant. A good rule of thumb is to take the last two digit of the pH of the wine and keep this level of free So2 in the wine. A wine that are at 3,45 pH will required 45 ppm free So2. 3,30 pH will required 30 ppm free So2. This is for a red wine, add 10 ppm more for white wine that are more sensitive to oxydation. Avoid going higher than 75 ppm. So at 3,80 pH you will target 75 ppm maximum.
I hope this can help others too.