Potassium/Sodium metabisulphite

[mak]

Hi guys

I have read extensively about campden tablets and all the many forumers have posted contradictory comments regarding potassium metasulphite.

1. They say potassium metabiasulphite kills yeast.

Qns: Is this true? I read that some forumer threw potassium metabusulphite into the juice to clean it before throwing in the yeast. He reported that fermentation was non existent for the first few days but rapid bubbling was seen after that. He attributed this to the sulphide wearing off. Is this true?

2. Then I researched more and someone wrote that the yeast we buy for brewing is different from stray yeast. As opposed to bought yeast, stray yeast are not resistant to sulphide

Qns: if that is the case then wouldn't it be impossible to stop fermentation with potassium metabisulphite. Say for example I have fermented the juice for 4 days. It is yet to ferment dry and I like the balance between the alcohol and sugar levels. I decide to maintain this by throwing in potassium metabisulphite. If store bought yeast are resistant then wouldn't this technique not work?

Thanks!

 

[Yooper]

1. No. It doesn't kill yeast in normal dosages. It may stun them if too much sulfite is used, but winemakers routinely use sulfites as an antioxidant and preservative. Wine yeast is specifically bred to be tolerant to sulfites, while wild yeast is not. Still, more than 50 ppm can be detrimental to a good yeast reproduction so usually you wait 24 hours after sulfiting a must before adding the desired yeast.

2. Correct. Mostly. I'm sure that some wild yeasts are more tolerant than others.

Stopping a fermentation is like stopping a freight train. Most people don't have good luck with doing it without causing some off-flavors from stressing the yeast. If you use enough sulfite to inhibit fermentation, you will have a foul tasting beverage. In less than 50 ppm, sulfites aren't above the taste threshold. Over that, there might be a discernible sulfur flavor, plus the stressed yeast from oversulfiting might put off bad flavors.

Stabilizing and sweetening are usually done after fermentation and after racking the cider off of the lees. Then, sulfites and sorbate together are added to inhibit yeast reproduction. (Sorbate doesn't kill yeast either, but does inhibit yeast reproduction, and it works better in the presence of sulfites). Then the cider can be sweetened to taste without further fermentation.

Some people have had good luck with chilling a fermentation down to stop fermentation and then stabilizing, or with pasteurizing a sweet cider to stop fermentation, but I've never been able to do it properly.

 

[CidahMastah]

My experience with the sulphur smells of k-meta is that they will (in my experience) always age out if you keep your cider/wine under an airlock for bulk aging.

Concur with Yooper on the rest.

The other thing is PH is a factor with sulphites. If you have a low hacid, high PH liquid, sulphites won't be effective. As a rule I have read you want a starting PH of 3.8 or lower to have effective use of the free so2 in k-meta. The higher the acidity (lower PH) the less k-meta you need to achieve you desired results. Once you get to a PH of 3.0, I believe sulphite isn't needed to protect teh wine/cider. However I am not saying to acidify your starting batch down to 3.0 !! Just giving you some facts I have read over the years.

Another point to mention is that if you accidentatlly over sulphite, you can give your wine/cider a couple of "rough rackings" and effectively remove somewhere in the neighbor hood of 22PPM (at most). The key is, to put in the right amount from the start.

As a general rule, you can rarely go wrong with 1 tablet (30PPM) per gallon.

 

[mak]

Thanks!

 

[simont]

I've been looking around and can't find much on using potassium metabiasulphite in beers - specifically fruit beers. I have a low gravity wheat I want to add watermelon juice to. I've seen Dachs and others brew a watermelon wheat and the watermelon juice is fermented out when added to beer in secondary. I've cold crashed my beer and want to split into two experimental batches - one with potassium metabiasulphite added to kill (retard?) the saccharomyces so the watermelon juice is not fermented by residual yeast (1056). The other batch I'll just add beer to the juice and let whatever fermentation takes place happen naturally.

So can I use potassium metabiasulphite to kill / retard / or otherwise stop additional fermentation by sacchromyces? Or is sacc resistant to potassium metabiasulphite.

Will potassium metabiasulphite add off flavors?

What dosage should I use?

Thanks all!