First infection

You're 99.9999% likely fine - the likelihood that something wild (read: not bred for hundreds of years to tolerate alcohol) could outstrip a wine yeast is very small in my opinion.

71B is a weird strain. I've had it go past 16%, some people say it never goes past 14% for them, and one person even claimed they got it past 20% (I think most of us guessed a math error of some kind in that case since the person would not explain their method nor their honey amounts or starting gravity vs finishing gravity, etc).


And hey - even if something wild did get in there, if it keeps tasting and smelling good, then it IS good. ;D

CG's right - we need to know a bit more about what you did (process, ingredients - amounts of each as well as the list, rehydration method, temperatures, etc.) and then we can possibly help out more. But it is not uncommon to have 71B go past its nominal 14% ethanol tolerance.

Don't worry - you can wait until either it stops or goes completely dry, then you can stabilize and backsweeten the mead to taste. It really isn't difficult, and after a few months' aging I doubt if you could taste the difference between a mead that has naturally stopped at a gravity above total dryness, vs. one that had been backsweetened.

Hmmm... it looks like you may not have accounted for all the additional water that the fruit would have added. Unless you smashed the thawed fruit completely, and then pressed the liquid out from the pulp, it is very likely that your measurement of OG didn't yet have all the fruit water in the mix.

Fruit generally are 80 to 90% liquid, and that is usually only around an SG of 1.040-1.060. The addition of so much fruit to your batch undoubtedly diluted your honey more than you think. I doubt that you're up as high as 18.75% ABV... from my back of the envelope calculations, it looks to me that you might be more in the 16.5 to 17% range. That's still a healthy dose of ethanol, but it is significantly less than you were thinking and it is within the capability of 71B in a properly managed fermentation.

CONGRATULATIONS! You managed this ferment very well!

Oh, and the likelihood of contamination in anything that high in ethanol content is almost vanishingly small. No wild yeast that I've ever seen has taken any of my batches anywhere near that high of an alcohol content, and that much ethanol usually kills most spoilage organisms.

It's highly unlikely that it'll go that far, but it was pretty unlikely to get to where it is already!

I wouldn't worry at all. What's done is done - contamination is a difficult thing to happen, and if it did happen, and it happened to be by a yeast/bacteria that can go to 17.5% ABV then all you can do is hope it'll still be tasty.

It's possible you were contaminated, but it seems much much more likely to me that 71B simply went that far.


Wait till it finishes fermenting, follow normal racking and aging proceedures (don't leave it too long on 71B lees, they are not good for lees aging) and see how it does. I'm betting it'll have some burn from the ABV for a year or two, but other than that (and possibly needing some backsweetening) will be fine.


EDIT: and as Wayne says (darn, I should have caught that!) it's likely your SG was actually lower than your reading due to fruit juice still trapped in the fruit. As they broke down and released juice your SG would have dropped as well. Still high ABV though, but it means you're definitely within the range of ABV that 71B can pull off.

Sounds like you may have been TOO nice to that yeast.

Are there actually spoilage organisms (other than acetobacter) that could survive that much alchohol? If it were wild yeast, that wouldn't really count as an infection in my book, just an unexpected twist.

koko0011 said:

Wayne, I am just a little confused by "Fruit generally are 80 to 90% liquid, and that is usually only around an SG of 1.040-1.060". Does this mean fruits give out different amounts of water at different gravities? Can you help me understand what you are saying since I am pretty sure that is not it.

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I think (and I could be wrong) he's saying that fruit juice (the part of the fruit that stays in your mead) is around 1.040-1.060. So that 80-90% liquid is lower gravity than the must you've added it to.

What I meant to say was that fruit can be thought of as consisting of liquid (water plus dissolved solids, primarily sugars) and solid matter. Most of the volume of any typical fruit is that sugar-infused water component. The insoluble solids (plant cellulose primarily) are a smaller fraction of the total volume. Each specific fruit is of course different in water and sugar content, and there are also differences between ripe and unripe fruit, but for estimation purposes you can use 80% and 1.050 as rough approximations of the amount of liquid that you derive from your fruit, and the SG of that liquid.

There used to be a great table of fruit water and sugar content out on the web, but I can't seem to find it anymore -- too much wordy drivel about dieting and the like to sort through now. Maybe Medsen knows where it is; if he does I'm sure he'll chime in with a link.

But, regardless of the actual values, if you make a simple assumption that 80% of your fruit (by weight) is water containing dissolved sugars, with the liquid at around a net specific gravity of 1.050, then your 18.75 lbs of fruit yields around 15 lbs (6.8 Kg) of liquid. Pure water weighs very close to one kilogram per liter, or around 3.785 kilograms per gallon. A liquid that has a specific gravity of 1.050 weighs 1.050 x 3.785 = 3.975 Kg per gallon. That means your 6.8 Kg of fruit liquid was approximately 6.8/3.975 = 1.71 gallons in volume.

You can now use the equation S1*V1 + S2*V2 = St*Vt to figure out what the net specific gravity of your mixture is. You have 21 lbs of wildflower honey dissolved in 3 gallons of water. That should be an SG of around 1.155. So, for this case, S1 = 1.155 and V1 = 4.8, S2 = 1.050 and V2 = 1.71, and since Vt = V1 + V2, Vt = 6.51 gallons.

Then (1.155*4.8 + 1.050*1.71)/6.51 = 1.127, and that's the net SG of your must with the fruit added. Now this is a very rough approximation, based on some wild assumptions about the water and sugar content of your fruit, but it is likely to be closer to actual than your first measured SG, since there would have been a lot of that fruit liquid still trapped in the fruit when you first made the measurement.

If a must at OG of 1.127 ferments to complete dryness, that would yield an ABV of around 17%.

Great advice everyone, I'm learning a lot by reading this post. One thing I'll chime in on: If you happen to have both a refractometer and a hydrometer, you can take a reading of both when it finishes fermenting and figure out what the actual starting gravity was by using some calculators that are available online.

Also, I've heard of Brett infecting 13% wines, but I'm not sure about above 16%. It would likely take a pretty long time to ferment anything, so I guess it is not a very likely culprit.

The brsquared site has some detailed fruit information including juice yield (reported as cc/Kg). For the berries you are typically looking a 500-550, which would suggest around 1.25 gallons (usually I'd guess about 14 pounds per gallon - or around 1.4 gallons in this case). However, the gravity of berry juice is probably not going to be higher than 1.035, so Wayne's number is still a pretty good guesstimate.

That's the one I was lookin' for! Thanks, Medsen!

koko0011 said:

I am also interested in Shadar's comment about whether any spoilage organisms other than acetobacter can survive at 16%.

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Lactobacillus Trichodes can survive at 18%, Zygosaccharomyces Bailii has been documented in 21% ABV IIRC. So yes, there are spoilage organisms (including others) that can survive high alcohol but they are not common.

You probably don't have a spoilage organism or wild yeast. What you have is either 71B which has gone above and beyond the call of duty (which can happen) or you picked up a high ABV strain from your brewing area that floated in and has grown and taken over. Have you been using any Champagne yeast in prior batches?

I agree with your conclusion. Your 71B simply outperformed its rated ethanol tolerance by a few percent, primarily because you managed the fermentation so well. It is now settling down and it may end up leaving this batch close to where you wanted it to finish (albeit at a slightly higher ethanol level) to begin with.

However, just because it slows to an apparent stop now, doesn't mean that after a racking it won't start back up again. Many meadmakers have been surprised by bottle bombs from semi-sweet to sweet meads that they've bottled after they assumed that fermentation was over. If you ever bottle a mead semi-sweet to sweet, even if all fermentation has appeared to have stopped, stabilize the mead with sulphite and potassium sorbate first.

BTW, Kris has been on Gotmead in the past, but he hasn't been a regular contributor. I think that he supplies most of his meadmaking wisdom to those who frequent the Northern Brewer forum. BTW - he and I have some differences of opinion regarding some aspects of the meadmaking (and aging) process, but from what I've been able to determine, they're for the most part really just different variations on a mostly common theme.