Matt, I believe that, according to the paper in the link to practicalwinery.com from “young autumn”, the 0.57 factor accounts for the fraction of SO2 in the potassium metabisulfite. Then the 40-70% accounts for the free SO2.

Thanks for the reply Matt, I just have this image in my mind of the first person transporting what they believe to be plain juice and the look on the face after the first gulp which leads to the question of what the winery might have looked and functioned like in a desert? Maybe a heard of goats with skins attached to back packs wandering around in an endless circle… boggles the mind!

Hi Howard, this is a great question! I’ve been looking into this but haven’t found anything specific. So many resources claim that “winemakers have used sulfites for centuries”, however, there’s no explanation as to how sulfites were added or used. I’ll keep digging and let you know what I find out.

Just recently I came across some public domain books on wine making from the early to mid 1800s. Surely there is something in there that might give us a clue.

-Matt

Hey there young autumn, thanks for sharing the link. The fourth step addresses the difference between the amount of sulfites added and the amount that will remain free to protect the wine. According to Alison Crowe of the Winemaker’s Answer Book about 57% of the sulfites added will remain free. This sits in just about the middle of the 40-70% range discussed in the article you linked to.

If you take a look at the equation I divide by 0.57 which effectively increases the dosage by 1/0.57 = 75% to account for this.

Please let me know if I’ve misunderstood anything or missed something entirely. I strive to keep everything on the Academy website as accurate as possible and I’ll gladly make a correction if this seems off.

Cheers! -Matt

Another great question Jude! There are several things you can do to replace commercial fining agents and yeast nutrients. Stopping a fermentation, however, requires the use of a sterile filtration system. A sterile filter has openings of 0.45 microns or less and will catch micro-organisms as the wine passes through.

For many years egg whites and egg shells have been used as fining agents. When using egg whites you want to be really careful that everything you use is very clean and has been sanitized. Robert Mondavi used egg whites to clear some of his wines. I can find a recipe for this if you like.

The most common thing I’ve heard of wine makers using to provide yeast nutrients without using the additive is raisins. It is recommended you cut them in half to pierce the skin. I was once advised to use 3-5 raisins cut in half per gallon of wine. I don’t have any scientific information to back this practice up but it is something I’ve seen quite a few wine makers use.

Cheers Jude! -Matt

Hi Jude, great questions! When a wine ferments it is the sugars that are converted into alcohol. A finished with that is completely dry has no fermentable sugars left and therefore not sweet. For the most part there the only way to stop a fermentation is through filtration or by ensuring that the alcohol level gets too high for the yeast to keep fermenting and they die before the sugar is gone.

The wines that have lost their sweetness have probably fermented to dryness. The wines that are still sweet either have not finished fermenting or have stuck fermentations where, for some reason, the yeast has stopped consuming sugar. This can be because the temperature isn’t right, not enough nutrients, or the alcohol level got too high.

As for how much potassium metabisulfite to add to a liter of wine, that depends largely on your pH level. If you check out the chart on this page it will tell you what the ideal sulfite levels are for the pH of your wine. pH alters how effective sulfites are.

If you haven’t yet added any sulfites to your wine you could add 0.22 grams of potassium metabisulfite to reach 25ppm of free sulfur dioxide. This would be in the goal range for wines with a pH of 3.4 to 3.6 which is a fairly common range to be in.

Please post your pH if you happen to know it.

Cheers! -Matt