Yeast and alcohol levels

[Qopzeep]

Hi all,

As a beginning brewer I have difficulty coming to grips with how yeast affects the alcohol and sugar level.

Currently, I'm making a cider with a yeast strain (by Arsegan) which will give me a dry cider. However, I've also purchased a yeast which is marketed as a medium sweet cider yeast. It should reach a maximum ABV of ~10% according to the package. I'm guessing that's the maximum alcohol level the yeast will tolerate before they kill themselves. So, logically, when I add enough sugars, and the yeast hit ~10%, the remaining sugar shouldn't ferment, right? Which means that I'm left with a slightly sweeter cider than when I'm fermenting with the dry cider yeast I'm using now, which is supposed to get my FG down to 0.995 (from 1.062). So, using the medium sweet yeast, I wouldn't have to sweeten the cider at bottling time. Is this correct? And can I still get some carbonation if I bottle? Or is there an increased risk of bottle bombs? I'm assuming I shouldn't prime if there are still sugars left.

Thanks!

 

[lazarwolf]

Here's the hard truth about cider. You wont know until you taste it. You may not have to back sweeten with the medium sweet yeast, you may. You just wont know. Natural Carbonation of cider, in my opinion is best for dry ciders that are back sweetened, where you can be sure almost all of the sugar is consumed. So when you add your carbonation sugar you have more control. That's my 2 cents

 

[Yooper]

Remember that a 10% ABV tolerance is more of a 'more or less' type of estimate. In a happy environment, the alcohol tolerance can vary greatly and can be much higher than the manufacturer's published data. Adding sugar until the yeast die off usually results in sweet 'hot' rocket fuel that takes a couple of years to age out (some yeast strains will easily go upwards of 18% ABV).

That may work for your purposes, making a sweet apple wine. But it will not bottle carb, as you need alive and active yeast for that. Once the ABV is over the alcohol tolerance, it won't start up again even if fresh yeast is added, as a new yeast will just die of alcohol poisoning since it isn't acclimated as well as the original yeast which gradually got the alcohol poisoning. I hope that makes sense.

Think of it as a pot you have to cook a lobster. If you put the lobster in, and then bring it to a boil, the lobster will live for a while, then gradually be overcome by the hot water. Same is true with yeast, sort of. As the alcohol level builds, some yeast will begin to get stressed and die off, but not all, until they are completely overcome.

If you put the lobster right into the boiling bath, he dies instantly. The same (again, sort of, as it's not a perfect analogy) will happen with new yeast. You've got a 14%ABV environment, for example, and even if you toss in a fairly strong yeast like Champagne yeast, the yeast will not reproduce and ferment with that environment as alcohol is toxic to yeast.

For yeast to reproduce and ferment, they need to be in an environment that is not stressful to them.

I hope that all makes sense!

 

[Warthaug]

I wouldn't want to trust the rated alcohol level to stop fermentation - in fact, most yeasts have the same ethanol resistance (about 17%) if you trick them to not go dormant (i.e. through batch-feeding)*. While batch-fed processes have
zero to do with brewing, it does mean that slight variations in your brewing procedures can lead a yeast to crap out at alcohol levels very different from what it is "rated" for. I've pushed yeast well beyond their rated alcohol tolerances, and I've also had yeast crap out long before they were "supposed" too.

* http://www.ncbi.nlm.nih.gov/pubmed/3533426

Bryan

 

[Qopzeep]

Thanks for the replies everyone! I suspected as much. So I guess that you either sweeten with a non-fermentable sugar, using a campden tablet or pasteurise to get a medium sweet cider. Or keg and carbonate, but that's really not an option for me. I actually like dry alcoholic drinks, but I think sweeter would be better for my girlfriend. If she likes it, she might just put up with me brewing in our 377 sq. ft. apartment .

If you put the lobster right into the boiling bath, he dies instantly. [..] I hope that all makes sense!

Excellent comparison, it makes perfect sense. Just a bit gruesome for the vegetarian that I am .

 

[Yooper]

Thanks for the replies everyone! I suspected as much. So I guess that you either sweeten with a non-fermentable sugar, using a campden tablet or pasteurise to get a medium sweet cider. Or keg and carbonate, but that's really not an option for me. I actually like dry alcoholic drinks, but I think sweeter would be better for my girlfriend. If she likes it, she might just put up with me brewing in our 377 sq. ft. apartment .



Excellent comparison, it makes perfect sense. Just a bit gruesome for the vegetarian that I am .

Campden doesn't kill yeast- it's not clear whether that was the intention here or not.

 

[Qopzeep]

I thought it killed natural yeasts? I assumed it would kill my introduced ones as well. Thanks!

 

[Yooper]

I thought it killed natural yeasts? I assumed it would kill my introduced ones as well. Thanks!

No. It's pretty good at killing bacteria, and perhaps some wild yeasts, but not ale yeast or wine yeast (that's why winemakers use it).

It's an antioxidant and preservative, as it binds with wine so that oxygen can't. But it won't kill yeast, at least in 'normal' amounts. If you used a ton of it, it probably would, but then the wine/mead/cider would be undrinkable.

 

[Qopzeep]

Thanks for clearing that up