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How does this happen ... would i be running a risk if they were in the same cupboard together or is it only a contact/physical contamination thing? I can't find much info other than that it can happen if you not careful sanitising.
I went through my old microbiology lab books and found a group of chemoheterotrophic bacteria that some of us may find familiar. It is possible that these bacteria could use sorbate to proliferate, and taint mead.
These are acetic acid bacteria which are used in Mother of Vinegar for making vinegar; and they oxidize primary and secondary sugars in fermenting liquids. In our case we are talking about conversion to keto-sugars: sobital to sorbase, mannitol to fructose, and erythritol to erythulose.
The good news is that these little beasties need O2 in order to carry out their conversion and oxidation reactions (Gluconobacter sp. and acetobacter sp. are the two Genus of the bacteria I'm talking about). They are markedly acidophilic growing in pH as low as 4, with an optimal pH in the range of 5 to 6.
For me that means that I will keep my pH range in the low threes, and rack my meads to corny kegs that have been evacuated of 02 and infiltrated with C02. In this case the sorbate should be sufficient to stabilize and prevent refermentation. The low pH and anaerobic enviornment will prevent the acetic acid bacteria from oxidizing the ethanol and other available substrates into acetic acid.
I'll follow this post with an extended excerpt from my reference source along with a bibliography.
The degasser is used to agitate the mead to get as much CO2 out as possible for a still mead or wine. Still an anaerobic process as the layer of CO2 shouldn't be disturbed on the top of the must. Manufacturers do this more for a final end product look and feel as most wineries would call their wines champagne if it weren't still.
According to the new BJCP guidelines, if there is a little CO2 in the must, it's called petulant. If there's much carbonation, it's called sparkling and otherwise, no bubbles means still.
Mostly de-gassing is done when the wine or mead is not giving up the last of the CO2 it's been producing. You'll see this when you get a cheap wine at the store, and it foams when you pour it into a glass. I've degassed wines before in order to get them perfectly flat, but they are the exception rather than the norm.
CO2 as it relates to Acetobacter sp. is actually a good thing because this particular beastie needs an AEROBIC environment to carry on it's evil work (unless you started out to make vinegar) in your mead or wine.
So when I want to put an un-sorbated and un-sulfited mead on tap, I go to a Corny Keg from the Carboy, or do primary in a Corny Keg. After I sanitize and I flood it with CO2, I rack from the primary Corny which is also flooded with CO2 and seal it. I do check the pH before I go forward to make sure it's in the 3.3 - 3.5 range to keep the Acetobacter sp. beasties at bay.
Here's a link to a post I made last year about degassing, and there are some other good posts in that thread about it too:
That kind of depends. It's used as more of a descriptive term now than anything else. However, if you enter a mead as still and it has more than a few bubbles, being petulant, it's marked against it as a defect. However, the judges are usually pretty kind (at least the ones I've had experience with) and will modify your entry sheet to be able to fairly judge it.