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Old 08-06-2008, 01:27 AM   #1
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Default Head Space/Oxidation Question

I have been reading about oxidation and head space in the fermentation vessel and I'm sort of puzzled. I think I theoretically understand that head space can lead to oxidation (no matter whether we're talking about beer, cider, mead or wine)...not so much a problem in the primary, but more so in a secondary. Yet, I don't see much discussed in the forums from a practical point of view.

Let's say I have 5 gallons of Ed's Apfelwein in a 6.5 gallon carboy and I let it ferment for a month or so (I know, Ed says no need to rack, but I want to do something with peaches). I want to put some peaches in a 7 gallon fermentation bucket, so I rack it over top of the peaches with some enzyme. Now I let it set for 4 months or so. QUESTION 1: Is oxidation going to be a problem because of my primary being too large for the 5 gallons? QUESTION 2: The head space in the bucket is huge...is this going to give me oxidation problems? Normal store-bought fermentation pails would seem to almost always be too big for most "normal sized" brews.

Changing the facts a bit (and maybe making the issue even clearer), let's say I have a 4 gallon bucket in which I mix 1 gallons of must with fruit or whatever. QUESTION 3: Is this bad practice?

QUESTION 4: If these situations present problems, will the addition of ascorbic acid solve them? If so, in what quantities?

How do you determine or select the size of your fermenters?

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Old 08-06-2008, 01:44 AM   #2
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With wines, I primary with just a towel over the fermenter to keep out critters. During this time, much co2 is being produced and the must needs oxygen. Within about 5 days (or when the wine/mead reaches 1.020 or so), I rack into a carboy and top up to within an inch or so of the bung. This keeps minimal headspace in there and helps prevent oxidation. Oxidized wine is said to be maderized- like sherry. It will have a sherry-like flavor and not be good at all.

So, I'd say that you can rack unto your fruit if you want to, but in a carboy, not a bucket, that late into fermentation. Headspace may more easily reduced in a carboy than in a pail.

I can't imagine how ascorbic acid could help prevent oxidation. I do use campden tablets at every other racking, but I still carefully rack without splashing and always top up wines, meads, and ciders.

The size of the fermenter depends on the size of the batch. A 3 gallon carboy for a 3 gallon batch and so on. Not in primary- a bucket is fine. But as soon as the fermentation slows down (like I said, to 1.020 or so), it's transferred to a carboy and topped up.

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Old 08-06-2008, 09:54 AM   #3
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<WARNING! SCIENCE!>
Ascorbic acid is a strong reducer and will react with oxygen before the other aldehydes, esters and god-knows-what in the wine will. So yes that might help. One problem though, dehydroascorbic acid might have a flavour and you may not like it. Maybe you can try it first, dissolve some ascorbic acid in water and wait for it to oxidize. It will turn pale yellow/orange when it oxidises so you'll know. Then taste it.

Another option is to add a part of you sugar when you rack. That way the yeast will consume all oxygen and not much extra alcohol will be formed. You will have more yeast though.

I just did a quick back-of-the-envelope and it seems that 1 oz. of table sugar should be enough to consume 27,87 gallons of air's worth of oxygen (incidentally this also means that 1 gram of table sugar will remove ~1 litre of oxygen from the head space).

That's not even counting the face that the oxygen will be partly flushed out of the carboy or bucket by the effervescent CO2
</WARNING! SCIENCE!>

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Old 08-06-2008, 11:01 AM   #4
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Quote:
Originally Posted by bluespook View Post
Let's say I have 5 gallons of Ed's Apfelwein in a 6.5 gallon carboy and I let it ferment for a month or so (I know, Ed says no need to rack, but I want to do something with peaches). I want to put some peaches in a 7 gallon fermentation bucket, so I rack it over top of the peaches with some enzyme. Now I let it set for 4 months or so. QUESTION 1: Is oxidation going to be a problem because of my primary being too large for the 5 gallons? QUESTION 2: The head space in the bucket is huge...is this going to give me oxidation problems? Normal store-bought fermentation pails would seem to almost always be too big for most "normal sized" brews.

Changing the facts a bit (and maybe making the issue even clearer), let's say I have a 4 gallon bucket in which I mix 1 gallons of must with fruit or whatever. QUESTION 3: Is this bad practice?

QUESTION 4: If these situations present problems, will the addition of ascorbic acid solve them? If so, in what quantities?

How do you determine or select the size of your fermenters?
#1 Oxidation will be a problem if you leave a wine for 4 months in a bucket. Buckets are quite porous to O2 so even if headspace was not a problem the bucket is.
Headspace is not a problem with primary only apfewein because the space has been purged with CO2 during the primary. However once you transfer a wine that is no longer fermenting to a container with a large head space you expose that wine to alot of O2 for a long period and will have a problem with oxidation.

#2 Primaries need to have a large headspace because the krusen will foam up and use that space. It is not a problem because during active fermentation the yeast will use some O2 and produce CO2 which displaces the unused O2 in the fermenter.

#3 This is no problem for a primary ferment but is a problem if you are racking wine onto fruit in the secondary.

Your primary fermenter needs to be big enough to contain the expansion of the foam on the must during primary fermentation.
Your secondary fermenter should be sized to match the batch of wine or beer and should be of a non porous material like glass or a BetterBottle.

Craig
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Old 06-06-2011, 02:22 AM   #5
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"Topped up" with what? Just water?
Thanks!

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Old 06-06-2011, 02:38 PM   #6
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Bluespook, oxidation is quite real. If you take a bottle of Madeira wine or Sherry and smell it, you'll know what oxidized mead or wine starts to smell like. In some cases it can actually be desirable, but most of the time, it is considered a major flaw. It can be prevented by limiting exposure to oxygen and avoiding high-temperature storage.

#1. The size of the primary is irrelevant. Bigger is better. Bigger means never having a problem with MEAs and having to mop up a big mess. In a closed container, an active fermentation will absorb and bind up the oxygen, and the large amount of CO2 produced will chase out any remaining oxygen, nitrogen, and other air components. As noted above open fermentation can be done, and while the yeast are active, you won't develop the oxidized aroma.

#2. Leaving mead in a HDPE plastic bucket does not protect it from oxygen. The HDPE plastic allows oxygen to pass through so even if there is no headspace in a bucket, the oxygen absorption will continue. With that said, there are some folks who age batches long-term in a bucket. BrewBoyTrev over on the Northern Brewer forums has done this with success. He has done it with fruit as well. I'm not yet convinced enough to recommend this approach, but if you try it, I hope you'll post up and tell us how it goes. Perhaps you and Trev can teach us all something.

#4. Ascorbic acid will not prevent oxidation. In wine trials where they have used it with white wines they actually found that bottles treated with ascorbic acid actually has a faster rate of oxidative browning than occurred without ascorbic acid. I'm not sure of the mechanism for this as ascorbic acid is an antioxidant, but in practice, it interacts with other components in wines to create more oxidation. Sulfites work better to prevent oxidation in wines (and we presume in meads as well).

There are several ways to deal with headspace after fermentation is finished. This thread discusses several.

One other suggestion I'll make is to consider shortening the time you leave the fruit in. With fruit pulp in the lees, there is a higher risk of developing sulfur odors. Secondly, excess time with fruit pulp/seeds often extracts bitter tannins and vegetal odors. Most of the good stuff (aroma and flavor) that you want from fruit will be extracted by an alcohol solution (mead) within a few days (7-14). Beyond that, you aren't getting useful stuff, but may be getting the problems I mention. With this in mind, you may be okay racking onto a fruit in a bucket as a secondary, and then transferring back off the fruit into a carboy after a few days.

With melomels, I find oxidation really can occur quickly and I try to protect my fruit meads with sulfites and limited air exposure. Traditional meads seem much more robust, and less prone to oxidation. Many people will keep a traditional mead in a container with excessive headspace and have it turn out fine. Nevertheless, with enough air exposure, you can create oxidized, sherry aromas in mead - done that.

Perhaps an even bigger concern than oxidation is the chance for spoilage organisms. Acetic acid bacteria need oxygen to grow. Sulfites will not stop them. Alcohol levels in most meads will not stop them (they can grow in 17% ABV). The only thing that will reliably stop them is having no oxygen. There are other spoilage organisms that also like air, and the best way to prevent them is make sure there is no headspace full of air.

I hope that helps.

Medsen

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