How do you find the alcohol % tolerance of yeast?

[Jman]

So i've been keeping a yeast colony alive for some time that i made from a cider batch a long time ago, and ive used it in some of my ferments with good results. I want to know how to calculate what % of alcohol by volume i can push this yeast to so i can use it for fermenting washes for distilling. I was thinking of starting high with sugar and calculate the alcohol % after each wash decreasing the amount of sugar in increments each time, and when it started going down I know i had reached the point where it was at its maximum, however wouldn't the residual sugar left over mess up the hydrometer alcohol % readings? Then I thought try the reverse, start too low with the sugar added and do several batches with the yeast and keep adding sugar each time until the alcohol % measured on my hydrometer stopped rising, then I would figure this is the alcohol tolerance of my yeast. Would this method work? Is there a better way to figure this out?

Does anyone know the method used to calculate what % alcohol i can make from my yeast?


Thanks,
Jman

[Hawke]

Depends on whether you are after fuel or quality spirits on how far you push your yeast. The closer you get to the tolerance level, the more off taste you get. (that is why you have to carbon filter Turbo's)
That said, you can cultivate your yeast to a higher tolerance. To do this, you keep going to heavier and heavier washes. The strongest of the colony will survive, but may take several years to accomplish.
For most flavored spirits, most won't push much over 10%. For neutrals, much over 14% and you start needing carbon to clean it up. Some have success going higher, but it's not the norm.

Bakers yeast is supposed to be able to handle 14%.
A champaign yeast like ec-1118 is in the 16 to 18% range.

[rad14701]

Jman, I think your second method is the best... In fact, you can probably preform the experiment with a single wash...

Start the wash with less sugar than you know the yeast can tolerate... Let the wash ferment to completion... Then add a bit more sugar and let that ferment... Repeat...

Once the wash no longer kick starts back into fermentation mode, or the specific gravity indicates that fermentation has stalled, the amount of sugar before the last addition is about the most the yeast can handle...

Then you can try another wash with that amount of sugar and see how well it ferments... You should be able to adjust the sugar up or down, by small amounts, to fine tune if desired or required...

You should be able to condition your yeast for higher tolerance once you know the upper limit of viability but, like Hawke said, it might take time to refine it to not render off flavors and smells... I guess it's a matter of how much time and effort you are willing to invest in the venture...

You may also need to monitor nutrients depending on the wash/mash used... Also, as you push to the far upper limits you may end up with a yeast strain that is recipe sensitive and not tolerant of variations... And, last but not least, pH may fall into play... Oh, the complexities...!!!

Would be interesting to hear the results if you decide to give it a go... Good luck...

[muckanic]

The problem with creeping the sugar up is that the amount of live yeast initially pitched makes a huge difference to final attenuation, as does anything that improves that yeast's ability to replicate before it starts to ferment (as in oxygenation and/or presence of unsaturated fatty acids). Otherwise, you wind up waiting for months for a result, and probably get hit with a lot of misleading byproducts as well. If you're going to creep the sugar up, I would recommend doing it in separate ferments each time. The volumes don't have to be big, and in fact an easy way to go would be to make a small test ferment, discard the liquid and keep the yeast, then repeat at a stronger gravity.

[rad14701]

Good points, muckanic... Perhaps both methods could be attempted... After all, the stepped method only requires one small fermenter... The only advantage of stepping is that only the hardiest yeast will survive and multiply, which is the yeasties desired, and they'll have plenty of dead relatives to eat...

[Jman]

Thank you for the replies. I am planning to use the yeast colony for fermenting wash for use in spirits for human consumption not fuel, so thats why I want to know the maximum tolerance of the yeast. That way I can make my calculations so the yeast isn't pushed to its maximum, therefore producing a better tasting spirit. I will try your suggestions rad14 and muckanic- thank you for your replies. The yeast originated from wild yeast on the apples when i got them, thats why i dont know what the % might look like. I have kept the colony alive to use in future cider batches, but now wonder if they would produce a fair % abv in my washes for distilling. How do the companys that sell the brewer's yeast estimate their yeast's tolerance level? I understand that yeast is living and therefore hard to calculate it down to a T as it is constantly evolving and changing, but do they use the same methods suggested for figuring this out?