Potassium Metabisulfite: When?

[SantArsenio]

First post. I'm sure this has been asked. Appreciate your patience.

I make red wines, typically Sangiovese, from crates of California grapes in the Fall.

(1) I've read about adding K-Meta at the time of crush. My concern is that this would interfere with the yeast I will add shortly thereafter. (I once added K-meta to a crush and then started fermentation and the result that season had a rotten egg smell that took a lot of time and work to blow off. I am not sure it's related, but I am suspicious. So I don't do it anymore). For those who add K-Meta at the crush, how long do you wait before pitching the yeast?

(2) Are you adding K-Meta during secondary fermentation (i.e., after pressing)?

(3) Are you adding K-Meta at "each" racking, or just before bottling?

Thank you,

 

[kevinlfifer]

K meta prior to crush is to weaken wild yeasts so you can control which yeast is dominant. I use it as a mist sprayed on the grapes, then wait 24 hours. (2 TBS per Gallon of water)

I never use it again until fermentation is complete. Then for me, 1/2 tsp per 6 gal.

For each racking or prior to bottling, 1/4 tsp or less per 6 gal.

That's just me. My wine usually cellars for about 4-6 years now.

 

[winemaker81]

Welcome to WMT!

1) The rotten egg smell was not from the K-meta -- that from hydrogen sulfide (H2S). Too much K-meta produces a burnt match smell, which will dissipate with time. H2S is produced when the yeast is stressed, typically by having insufficient nutrients.

Most people who add K-meta at crush time wait 24 hours before inoculating.

2) There's actually only 1 yeast fermentation, although we find that professionals sometimes get this wrong. Regardless of whether the wine is in the primary fermenter or secondary storage, it's all one fermentation.

Most folks don't add K-meta until fermentation is complete.

Note: Malolactic Fermentation (MLF) is the real secondary fermentation. Since MLB (malolactic bacteria, not baseball!) is sensitive to K-meta, folks who want MLF don't typically add K-meta until the MLF is complete.

3) I add K-meta at each post-fermentation racking, every 3 months during bulk aging, and at bottling time.

 

[mainshipfred]

You may get differing opinions which will more than likely all be correct.

1. I don't typically add any at crush unless the grapes don't look the greatest. Remember the grapes come with a sulfite pad. I think people do add it at time of crush at the rate of 25 to 50 ppm. Waiting a day should be long enough to wait before adding the yeast.

2. Secondary is a loose term so I don't know if you are referring to secondary as in kits or MLF. The reason I don't add any at crush is the MLB's sensitivity to SO2 levels.

3. Like Kevin I do a heavy dose once MLF is complete, usually to the rate of 60-70 ppm. Then if in barrels every couple months but I measure what it takes to get it to around 40 ppm. In carboys I probably don't add anything for 6 - 9 months. But I do measure it periodically.

 

[BarrelMonkey]

1. If I have nice clean grapes, I don't add at crush unless there are extenuating circumstances (eg I am not going to be able to pitch yeast for a few days). Otherwise, as others have said 25-50ppm based on must volume. (If you're in NJ and receiving CA grapes, it might be good insurance to add Kmeta but I'd make sure that the supplier hasn't already done so...)

2. For reds I typically want my wine to go through malolactic conversion, so I don't add any K-meta after pressing. Once ML is complete I will add according to type of wine and pH. Recently I've come to favor adding a high 'loading dose' initially, since a lot of it will get consumed immediately.

3. I add K-meta every month for wine in barrels, every 2 months for wine in carboy/keg, amount based on results of FSO2 assays and target FSO2.

Welcome to WMT!

 

[David Violante]

Welcome to WMT!

 

[Jovimaple]

Welcome to WMT!

 

[sour_grapes]

Welcome aboard!

 

[tjmeyer]

Welcome to WMT!

1. Yes! I absolutely add potassium metabisulfite to freshly crushed must. This doesn't mean it needs to be done, necessarily. As a business, I can't risk 55g+ (barrel fermenter size) of product to a particularly aggressive yeast strain that happens to be around that year--yes, every year is different and I don't always want to have to inoculate with a faster/more aggressive yeast than whatever is around that year. A much, much better way to handle this is to freeze your must completely before ferment. This not only controls wild yeast, but also significantly improves juice release from the grapes. Having the space to freeze this much must is a problem in it's own right, but it is a great option and done regularly.

SO2 is not what you're smelling. It smells like spent fireworks and should dissipate quickly--within 48 hours, tops. The rotten egg is from struggling yeast and is correctable, but it takes a lot of patience.

None of the methods I have read so far are incorrect, they're just different. Thus the beauty of wine making!

2. Yes, to stabilize, not because of pressing. Again, my method is not the only valid method. In my case, my wine does not come into contact with any oxygen until barreling or bottling. Going to bulk storage is very closed and sanitary due to the equipment I'm using, so there's no need. However, I do add it at around 1.000 SG to force fermentation to wind down. I don't like to force yeast into the 0.998 region as it increases risk of acetic acid production, and that just doesn't sell and/or is prohibitively annoying to fix. Personally, if I want MLF, I just add lactic acid bacteria (LAB) 24-48 hours after pressing and stabilizing. I'm not a huge fan of lactic acid and actually prefer low malic acid to begin with in most of my wines.

3. During aging it depends and is the most variable. If barrel aging, yes, every 3 months or so and before bottling, @winemaker81 mentions this and I agree. I am currently in the process of removing barrels from the winery. I think they're great, they're classic, they look great, but I'm so tired of them. They introduce huge costs and risk. I am now aging in stainless with oak added and I no longer need to add any SO2, even at bottling, for an excellent wine! Worth it.

Cheers!

 

[Tripled92]

Welcome to WMT!

1. I can’t answer about adding k meta during crushing but i can answer about the H2S smell. This smell comes from when your yeast is stressed. Best to add fermaid O. We have found it’s best to add at the same time you put in your yeast. Directions on fermaid O says to add when fermentation begins but depending on yeast strain and time you add the yeast it may start in the middle of the night and yeast gets stressed so best to add right when you put yeast in. Secondly during the stabilizing phase if you still smell the egg smell add Reduless it will get rid of it, make sure you follow its directions because you need to rack off after a certain time period.

2. Confused what you mean by secondary fermentation. Ppl have a lot of different meanings of it so hard to tell which you are talking about.

3. We add it during stabilizing phase (after racked from fermented to carboy then degassed, then add k-meta to help protect it while in carboy). Then we add it again after the last rack which most of the time is our 2nd rack.

 

[Tripled92]

Welcome to WMT!

1. I can’t answer about adding k meta during crushing but i can answer about the H2S smell. This smell comes from when your yeast is stressed. Best to add fermaid O. We have found it’s best to add at the same time you put in your yeast. Directions on fermaid O says to add when fermentation begins but depending on yeast strain and time you add the yeast it may start in the middle of the night and yeast gets stressed so best to add right when you put yeast in. Secondly during the stabilizing phase if you still smell the egg smell add Reduless it will get rid of it, make sure you follow its directions because you need to rack off after a certain time period.

2. Confused what you mean by secondary fermentation. Ppl have a lot of different meanings of it so hard to tell which you are talking about.

3. We add it during stabilizing phase (after racked from fermented to carboy then degassed, then add k-meta to help protect it while in carboy). Then we add it again after the last rack which most of the time is our 2nd rack.

I do want to add is get the Scotts laboratory wine making handbook. Has description about every single yeast you can think of, reason I say this is some actually arent as stessed it’s just they have a high H2S production. For example BM 4x4.

Also depending on where you live you may want to send your juice to a lab, because unless you have the expensive equipment you won’t be able to tell your YAN requirement. So just because you add yeast nutrients it may not be enough unless you have your YAN readings to know the exact amount you need to add.

Hope this helps!