Other To use potassium sulphite or not to use potassium sulphite

[Gaius Churchill]

Hello! This is my first kit I've ever made, for context, however, I am about to stabilize and begin clearing my Fontana Cab kit. Instructions say to add Potassium Sulphite and Potassium Sorbate. I understand the P. Sorbate stabilizes the yeast, but I can't seem to find a satisfactory explanation on what the Sulphite does. My friend, who got me into this, says he never adds the P. Sulphite due to headaches and I am contemplating doing the same. Does anyone have any insight on this?

Thanks!

 

[sour_grapes]

Potassium metabisulfite (known as "K-meta" around here) serves two important functions. It helps prevent premature oxidation (because it scavenges oxygen) and it inhibits microbial spoilage.

I would skip the sorbate unless you are sweetening the finished wine ("backsweetening"), but add the K-meta.

ETA: Oh, and, for most of the population, sulfites don't cause headaches.

 

[Gaius Churchill]

Interesting, thank you. What role does sorbate have in backsweetening?

 

[mainshipfred]

Interesting, thank you. What role does sorbate have in backsweetening?

When you ferment to dry there is no food (sugar) for the yeast so it basically stops being active but doesn't die. The sorbate keeps it from activating itself once the additional sweetener is added. It does not stop fermentation just simply keeps it from reproducing.

 

[winemaker81]

@Gaius Churchill, be leery of trusting your friend's POV regarding sulfite. Paul's and Fred's statements are easily verified with a web search of organizations that perform winemaking research.

K-meta functions by binding to contaminants (including O2), rendering them harmless. Failure to add K-meta to wine shortens the shelf life of the wine.

 

[sour_grapes]

Interesting, thank you. What role does sorbate have in backsweetening?

As Fred said, sorbate inhibits further fermentation. Let me say a word about how.

For as simple as they are, yeast have a complex lifecycle! Wine yeast have both haploid and diploid phases. They can reproduce either sexually or asexually (by budding). Mostly, they reproduce by budding and then splitting into daughter cells. Sorbate binds to the outer surface (I don't know the details) and prevents them from budding and splitting. Hence, sorbate does not kill live yeast, but it acts as "birth control" on them.

So, if you add sugar (backsweeten) without sorbate, the live yeast that are left from the fermentation will feed, reproduce, and form a large colony that will eat all your sugar. If, instead, you add sorbate, the few remaining live yeast will not be able to reproduce, and they won't be able to grow a colony to eat your sugar.

 

[Old Corker]

@sour_grapes
Thank you for that. Best description of what Sorbate does I’ve seen. One question. If you filter through a 1 micron filter does that remove all the yeast cells?

 

[sour_grapes]

I am no expert, but my understanding is that you need to use a 0.45 micron (absolute) filter.

 

[mainshipfred]

I am no expert, but my understanding is that you need to use a 0.45 micron (absolute) filter.

That has always been my understanding as well. I think the best we as home winemakers can do is .5 nominal.

 

[gsorrells]

You have received sound advise. We have a small commercial winery. Adding back sugar after your primary fermentation will (in most cases) cause fermentation to restart and bulge corks - unless you use sorbate. And, yes, it takes a .45 micron filter to filter the yeast out - using a cartridge filter, not a plate filter. However, if you are drinking your wine within a year or so of bottling, you can get away with a 1 or 2 micron filter - if you have fermented it dry.