How many times to add potassium metaibisulfite ?

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CatsCradle

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Hi everyone, im fairly new to brewing/ fermenting. Its my understanding that potassium metabisulfite is used to neutralize wild yeast and to combat oxidization. I read that you need 1/4 teaspoon per 5 gallons of must. My question is in my current batch (this time its a cider not a mead) I have used a lot of fruit additions and as such have racked quite a few times 3 times. Can I add a dose, 1/4 teaspoon of metabisulfite after each racking or do I only add it once? Any input would be greatly appreciated
 

bernardsmith

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Depends. If you are racking from the secondary every couple of months then you could add K-meta into the empty carboy and rack onto the compound. K-meta will neutralize and the free SO2 which is what you are using to inhibit oxidation will tend to become bonded to the O2 present and so unable to bind to molecules present later. I think the normal amount of free SO2 we look for is about 50 ppm. If for some reason you need to rack more often, my sense is that there will be enough free SO2 still in solution to allow you to forgo adding more every time you rack. The kind of wine you make is really not the issue, although mead makers tend to argue that mead is less susceptible to oxidation than fruit wines.
 
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CatsCradle

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Depends. If you are racking from the secondary every couple of months then you could add K-meta into the empty carboy and rack onto the compound. K-meta will neutralize and the free SO2 which is what you are using to inhibit oxidation will tend to become bonded to the O2 present and so unable to bind to molecules present later. I think the normal amount of free SO2 we look for is about 50 ppm. If for some reason you need to rack more often, my sense is that there will be enough free SO2 still in solution to allow you to forgo adding more every time you rack. The kind of wine you make is really not the issue, although mead makers tend to argue that mead is less susceptible to oxidation than fruit wines.
Thanks for the info! Can potassium metabisulfite slow or stop fermentation? I ask because my final gravity ended at 1.010, even after adding a pound of sugar
 
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bernardsmith

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Short answer is , yes. Longer answer is that K-meta cannot do very much to a large colony of very viable and active lab cultured wine yeast. It is used by wine makers to kill off indigenous (wild) yeast cells that may be in the fruit or stems of fruit they are planning to ferment. These yeast are not nearly as robust as the wine yeast you buy. That said, towards the end of a fermentation, after you have racked your wine several times there may be very few cells (relatively speaking) left in the wine and K-meta can eliminate many of those but typically, towards the end of fermentation when you are just about ready to bottle, if you are planning to back-sweeten the wine you add K-sorbate in tandem with K-meta. The sorbate prevents those cells not killed from reproducing so any sugar you added is basically untouchable to living yeast that might remain. Normally, you might stabilize the wine with these two chemical compounds on Monday and wait a week before adding any sugar. Of course, if you have a large enough colony of yeast simply adding K-meta is a lot like holding up your hands to try to stop the wind from blowing. It ain't gonna do anything. The yeast have been cultured and bred by the labs to be pretty much unharmed by K-meta although despite that most wine makers who add K-meta to their fruit will wait about 12 -24 hours before pitching their yeast because sulfur is a powerful enough bactericide.
 

DuncB

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I only have sodium Metabisulphite.
What strength should I use to give final rinse to bottles so residual liquid can do the deoxidising prior to counter pressure fill. Or concentration in filled keg before pumping it out with co2 before beer closed transfer.
 

bernardsmith

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Na -Meta and K-meta are essentially the same thing. It's the meta that has the power and not the metal (Na or K) but I suspect that a film of the chemical will do diddly squat in terms of inhibiting oxidization. You need the full measure in solution to allow all the free SO2 to be be able to bind over weeks to any O2 before the O2 binds to the fruit or the compounds in the honey (or the ethanol?) . Let's say the dose is 1/4 t for 5 gallons then you need that quarter teaspoon in solution to do the work. Like I suggested previously, you need about 50 parts per million of K-meta (or Na-meta) and that is what the 1/4 t provides in that volume of mead or wine.
 

DuncB

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Thank you. So a little bit of calculating for me scaling back to find the working " dose " to put in each bottle pre filling.

I think then I should use the starsan as before or the solution of Meta and flush this out of the keg and then inject in the working dose of Meta to the keg under pressure ( using CO2 ) and then fill the keg via closed transfer.

Very helpful thank you.
 

bushpilot

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Thanks for the info! Can potassium metabisulfite slow or stop fermentation? I ask because my final gravity ended at 1.010, even after adding a pound of sugar
Maybe because you added a pound of sugar.
 

bernardsmith

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Maybe because you added a pound of sugar.
Do you get bushpilot's post? bushpilot is suggesting that your mead finished at 1.010 because you had asked the yeast to ferment so much sugar that they succumbed to alcohol poisoning. Yeast have limited tolerance for alcohol. It acts as a poison and lab cultured yeasts are grown to withstand specific amounts of alcohol. Most wine yeast can tolerate about 14 -15 % alcohol in solution, some cells can tolerate higher concentrations but if you check the spec sheets published by the labs that grow the yeast you can see all the critical parameters that the labs "guarantee" any batch of yeast can withstand. Beyond those limits, all bets are off.

The metaphor I use is rope or chain. You buy rope with a breaking strain of say 1000 lbs. You might use that rope with a load of 500 lbs. It's guaranteed by the maker to withstand double that and in reality it might take 4 times (2000 lbs) what you are asking it to take, but if you apply 1,200 lbs and it snaps then that's your fault. If it stands up to 1,500 lbs then you can count your lucky stars, but you better know exactly what you are doing and you better be prepared to take full responsibility if anyone gets hurt or worse. But most people will use that rope well below it's guaranteed breaking load.
 

DuncB

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Certainly don't hang on that rope after it has survived a test to breaking strain. Hence second hand rope not good and don't use a rope that you find attached to a cliff. Who knows what adversity it has had to put up with.
 
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CatsCradle

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Maybe because you added a pound of sugar.
The 1.010 reading was before I added a pound of sugar. I added the sugar to see if it would restart fermentation which it did not. As I said after I added the sugar there was no visible signs of fermentation, but I am aware that 1 pound of sugar should add around 46 gravity points per 1 gallon. I racked a couple of times leaving some pretty large yeast cakes behind so I am thinking that the lack of fermentation is due to a combination of too many rackings and the use of sulfite.
 
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CatsCradle

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On a different note, I have a rather bad habit of sampling my ciders/ meads by extracting a small amount with a straw and putting it in a tasting glass to drink/ assess. I guess the reason I originally asked the sulfite question is that im paranoid that by taking these samples my cider might oxygenate. Is there a downside to using too much sulfite? I guess it would affect taste after a certain point. In my case I have only done two sulfite additions so not that much in my opinion
 
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