Originally Posted by Pogo
I seem to recall many posts advising the use of Campden tablets OR potassium sorbate at, I'm thinking, the bottling stage of winemaking.
All of this time I've been thinking that potassium sorbate was just the powdered form of Campden tablets!?!
Thanks Yooper, for pointing this out to me.
Let me go do some more research before I mess something up.
Campden tablets are either potassium metabisulphite or sodium metabisulphite not potassium sorbate. Metabisulphite is used to add SO2 to the must to inhibit bacteria and to prevent oxidation. Wine yeast are sulphite tolerant an so can be pitched in a must that has been treated.
When the wine is finished if you wish to stabilize the wine to prevent renewed fermentation you can add BOTH sulphite and sorbate together. This is done if you want to back sweeten the wine to produce a sweet wine.
Hydrometers measure the density of the must. When you dissolve sugar in water it increases the density of the liquid, meaning the liquid is heavier. The SG (specific gravity) scale on the hydrometer is a measure of the relative density of the must compared to pure water. A gravity of 1.100 is 10% heavier than water and 1.000 is the same weight as water. Alcohol is lighter than water so when the sugar is converted to alcohol the gravity can drop below 1.000. Because we know the chemistry involved in the conversion of sugar to alcohol we can estimate the alcohol produced in a must by the difference in gravity between when the yeast was pitched and when it is finished.