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Last week I started a cherry mead and discovered yesterday that it had turned to vinegar (and not even nice-tasting cherry-flavoured vinegar - it smelled and tasted awful, though the colour was great). I'm not sure how this happened, so I'm posting what I did in the hopes that someone can diagnose the problem before I try again.

  1. Boil 4 litres (I make mead in a 5L jar on my kitchen counter - my apartment is not big enough for rows of carboys!) of water for 25 minutes.
  2. Reduce heat to below boiling and add 1 kg (about 1L) of honey (plain, Billy Bee honey).
  3. Remove scum from surface until no more scum forms.
  4. Add 500 ml of washed, diced, pitted black cherries (tied up in a cheesecloth) to the water and honey
  5. Add 750 ml of black cherry juice (bought at a nearby health-food store), because I didn't have very many cherries left.
  6. Simmer for about 20 minutes.
  7. Cool, add to fermentation jar, pitch yeast (Lalvin champagne yeast).

An observation: this batch fermented far faster and far more vigorously and violently than any other batch! Almost all of the sugar was consumed by fermentation within 4 days. In all my other batches, it typically took 8 to 12 days for this much sugar to be consumed.

I have used this variants of this process (minus the fruit), steps 1 - 3 and 7 for almost a dozen batches (all successful so far) over the past two years, so I'm thinking the problem was in the fruit.

This was actually my second fruit mead - the first one was with strawberries, and they were thrown in at the beginning of the process (Step 1, when boiling the water), I thought it would be important to sterilize them. I later read that fruit should not be boiled, or pectin would form and result in a very cloudy mead (and yes, the strawberry mead was tasty but also cloudy), and also possibly affect the flavour.

So I've been wondering about where the failure was:

  • The cherries - Should they have been boiled, or sterilized in some other way? I have also read recipes that involve putting the cherries in during fermentation but to me that seems to carry an even greater risk of infection from outside sources.
    • Would I have better luck with frozen cherries (or other fruit), assuming that the frozen fruit is somehow sterilized before it's frozen?
  • The cherry juice - It was supposed to have been pasteurized, but I admit I opened it a little before I made the mead, just to taste it.
  • Bad luck??
  • Something else in this process that I missed?

It was also suggested to me by a friend that cinnamon has antibacterial properties so I should put 1 or 2 sticks in when boiling the water (they also said the juice of one lime would work as well, but I'm not sure about that and I worry it would have a strong impact on the flavour).

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If you simmered the fruit and juice for 20 minutes then the problem is definitely not wild yeast from the cherries. Any bacteria would be killed by a 20 minute simmer, anything about 150F and you are at wet pasteurization levels. Perhaps what you are tasting is the acid from the fruit in a super young mead? That would be very tangy and hoochy and maybe that is making it taste like vinegar? –  Graham Aug 30 '11 at 17:02
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I'm surprised that an acetobacter would move that fast. Have you seen a pellicle (sort of like skin on top of gravy)? If it were me and I had the space and containers, I'd keep it around and see if it got any better with time. –  baka Aug 30 '11 at 22:15
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@Baka: This batch did not have that, the surface was clear in the middle, and at the edges of the container there were lots of bubbles. I don't know if this could have improved, it smelled and tasted awful, and the sugar was almost all used up. I suppose I could have poured it back into a pot, re-pasteurized it, added more sugar/honey, and then re-pitched the yeast, but that's almost as much work as a new batch, and I don't know if that would actually work, or if it was chemically beyond repair. –  FrustratedWithFormsDesigner Aug 31 '11 at 3:59
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adding things during fermentation reduces the risk compared to adding at the start, During active fermentation, the yeast have taken a stronghold, removed most of the oxygen, and the pH of the mead will have dropped considerably, making it unfavorable for most other organisms. –  mdma Aug 31 '11 at 20:38
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I wouldn't say less risky if it's all cooked, but you're not boiling so there is still a possibilty of infection, although, this is only going to happen if the yeast are weak/underpitched. Adding uncooked material to the fermentor once fermentation has started, rather than at/before pitching time, reduces that risk. –  mdma Aug 31 '11 at 21:25

1 Answer 1

up vote 5 down vote accepted

How do you cover the 5L mason jar? Does it have any sort of airlock, and is there a means of preventing bacteria and/or fruit flies out of the jar? I ask because fruit flies carry acetobacter (they're also known as vinegar flies), and acetobacter turns alcohol into vinegar in the presence of oxygen. So if your mead was exposed to air and a fruit fly got in to it, it could well turn to vinegar.

If you're working with fruit - fresh, frozen, or otherwise unpasteurized - a good way to protect yourself is to add a bit of potassium metabisulfite to the fruit. ~200ppm is the threshold of detection. The effectiveness is determined by pH, but if you kept it under 100ppm you should cover all your bases - preserving, protecting against oxidation, and keeping it under the threshold of smell. Simmering the fruit, as you did, would have killed any baddies that came from the fruit.

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I take several paper towels and put them over the mouth, secured tighly with elastic bands. I did see a single fruit fly a few days ago, but that was after the brew had already started fermenting, I guess it's possible one of its buddies got into the mead. Ok, next time maybe I will put a bag over the jar and tape the edges. –  FrustratedWithFormsDesigner Aug 30 '11 at 18:43
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How would I measure 100 ppm of potassium metabisulfite? I guess it would be best to mix it in water with the fruit that's about to be used - would it affect the yeast when I add it to ferment? –  FrustratedWithFormsDesigner Aug 30 '11 at 19:00
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1 gram in 1 gallon is about 150 ppm. It scales linearly, so you can compute how much k-meta to add based on that. If you are using cultured yeast, the k-meta will not harm it as long as you keep the ppm levels low enough. I would shoot for 50-75 ppm, but you can go as high as 100. Before you innoculate with yeast, draw off about half a cup of your unfermented mead and stir the k-meta into this. Then mix this solution back into the batch. Then innoculate. –  JackSmith Aug 30 '11 at 19:18
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Hmm, if my mental calculations are correct, that should be 2 campden tablets for a 5 litre jar... and I guess if I go this route, I don't need to spend 25 minutes boiling the water at the begining, right? Is chemical sterilization as effective as boiling? –  FrustratedWithFormsDesigner Aug 30 '11 at 20:09
    
You can't sterilize with campden tablets. You can merely chemically preserve, meaning you can create a climate in which wild yeast & bacteria will die. I've never brewed mead, so I can't give advice as to whether or not you can skip the boil. I was only suggesting that you can sanitize fresh & frozen fruit by adding enough k-meta to it to kill the bad stuff. –  JackSmith Sep 1 '11 at 19:25

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