Sugar to yeast ration equation?

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gahover7

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I have looking online for some sort of equation or rule of thumb to calculate the sugar to yeast ratio during the primary Fermentation process to see whether it will produce a dry or sweet cider. For example if I do a 3 gal batch using store bought juice that has “X” amount of sugar per gal and I use a yeast with a 10% tolerance will my brew becoming a few points above or below so I know If and how much sugar I need to add. Thank you to anyone with advice
 

Toxxyc

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Nope. Your yeast will most probably consume all the sugars until past 10% ABV. Most modern yeasts will do 12% ABV or more, so if you're fermenting you're going to keep adding sugar until your cider gets to around that percentage (or much higher).

The only way to backsweeten a cider is to let it ferment to completion, then stabilize with preservatives (potassium sorbate and potassium metabisulfite to be exact), and then to backsweeten with your choice of sugar or syrup. Alternatively you can ferment to completion and use non-fermentable sugars to backsweeten it with, like xylitol or sodium saccharin.
 

Miraculix

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What I do with mead, is letting it ferment till completely dry, backsweeten it, bottle,cap and then pasteurize in the closed bottle. There's a thread in this forum that describes the process in depth.

You can also close the bottles and let the yeast start to ferment the sugar and pasteurize later, to create a sparkling cider. But be careful not to create bottle bombs this way.
 

madscientist451

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The only way to backsweeten a cider is to let it ferment to completion, then stabilize with preservatives (potassium sorbate and potassium metabisulfite to be exact), and then to backsweeten with your choice of sugar or syrup. Alternatively you can ferment to completion and use non-fermentable sugars to backsweeten it with, like xylitol or sodium saccharin.
As a homebrewer, you don't have to make a shelf-stable product. You don't need to use preservatives or chemical sweeteners. All you have to do is mix your sweetener of choice in the amount of cider you will drink in a week or less and keep it cold and you'll be fine.
I usually bulk age my cider in 1/2 gallon or gallon jugs. If I want a sweeter cider, I dump about 1/2 can of FAJC in a 1.5L wine bottle and then carefully pour the cider in. I keep it in the fridge and it gets consumed in a few days or a week at most. But I actually prefer small kegs and make up about a gallon at a time. If the yeast kicks off a little before I drink it all, it really doesn't hurt anything.
But I think what the OP is asking, is if he can simply boost the ABV so the yeast essentially dies from alcohol poisoning. Sure, you can do that, but the flavor will be more like a fortified wine than a cider, so it all depends on what you are trying to achieve.
There are many factors that determine how much alcohol your yeast will tolerate including the amount of yeast, are you adding nutrients, are you step feeding the added sugars or adding them all at once.
If the OP wants to try it, use some SO4 beer yeast, boost the ABV with enough sugar to hit 14-16% abv and see what happens.
 

Toxxyc

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OK so something to be clear on - the yeast doesn't die from alcohol poisoning. It just stops fermenting. If the conditions are good, it can start fermenting again. If you water down the solution, it'll ferment again.

I wouldn't bottle something that contains yeast and sugar if you don't know where it's going. I've got a scar to prove that it's not smart.
 

madscientist451

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OK so something to be clear on - the yeast doesn't die from alcohol poisoning. It just stops fermenting.
Here's my source: Mr. W.D. Gray mentioned below was a head of research for Seagram's had an undergraduate degree in Botany for DePauw, and earned a Ph.D. from the University of Pennsylvania, and was on the faculty of several universities including Ohio State.
One of the areas Dr. Gray focused on was the alcohol tolerance of yeast.

Selecting Yeast in Beer Brewing and Wine Making

Humankind has benefited from fermentation products, but from the yeast's point of view, alcohol and carbon dioxide are just waste products. As yeast continues to grow and metabolize sugar, the accumulation of alcohol becomes toxic and eventually kills the cells (Gray 1941). Most yeast strains can tolerate an alcohol concentration of 10–15% before being killed.

Link to article:

Specific study mentioned in article:
Gray, W. D. Studies on the alcohol tolerance of yeasts. Journal of Bacteriology 42, 561–574 (1941)
 

Toxxyc

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OK I'll admit - you have a source, I don't. I also have to point out that source is from 1941 :p

I'll read a bit into the article, but I'm still of the opinion that it doesn't kill the yeast, it "deactivates" them. I've seen it in meads - once you get to the tolerance you can add water and the fermentation will continue, even after some time.

EDIT: From the first page:

It is a well-known fact that in the commercial production of alcohol by fermentation there is a certain alcohol concentration which cannot be exceeded, regardless of the amount of sugar supplied to the yeast cell. It is obvious that after a certain period the yeast is no longer able to produce alcohol, and, since fermentation always stops about when the same alcohol concentration is attained (if the same yeast strain is always used), it is logical to assume that for every strain of yeast there is a maximum alcohol concentration above which the yeast ceases to function.

That last 5 words...
 

madscientist451

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Yeah, I've done the same thing myself, made a high ABV mead, and then thought I could add fruit and the alcohol would get fruit flavors out without kicking off fermentation. But fruit is 90+% water, the mead was diluted, the ABV lowered and the fermentation kicked off. But if you keep step feeding honey or sugar and just small amounts of water, eventually you'll create a toxic level and the yeast will die.
The study mentioned above is pretty old, but the research goes on, these days mostly about getting the most ethanol for the production of bio-fuels. The consensus is that ethanol is toxic to yeast and they eventually die.
 

Toxxyc

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Yes I'm sure some cells would die, specially in the test these guys did in that 1941 experiment. They stuck yeasts in a test tube with water and glucose, alongside a pretty low pH (although not out of the norm). They then fermented the mixtures at high temperatures as well, typically 30°C (and also tested at 35°C). You'll notice that the strains that performed badly were not S. Cerevisiae (the primary yeast we use for fermentation), and S. Cerevisiae actually performed remarkably well (well, most of them).

To boot, they only fermented for 24 hours, and the one strain consumed ~98% of the sugars during this time, before the test. My opinion is that they didn't give the yeast enough time, and it would have probably fermented past their measured ~11.5% ABV if they let it.

Finally, my opinion on the article: It's helpful, it surely is. To me it bears repeating with a more valid dataset though, namely:

1. Using modern yeasts. The yeast strains they mention are not really known to us in this day and age, and
2. Without abusing the yeast in the tests. Adding a yeast suspension to a glucose solution, with no additional nutrients for the yeast cells to consume, and then fermenting it WAY above the recommended temperature is not a consistent, fair or accurate test (in my eyes), and
3. With measuring the pH of the solution after fermentation. Fermenation drops the pH of a solution lower, due to several factors. Prior to fermentation they dropped the pH almost to the low limit that yeast likes. Yeast likes to ferment between 4.0 and 6.0 on the pH scale and I'm willing to bet money that if you adjust a sugar wash's pH to 4.3 BEFORE fermentation, you're going to go below it for sure during the fermentation. Sugar washes breach 4.0 on their own, without adjustment, on a regular basis (which is why we use sea shells or chemicals to keep the pH from crashing during the fermentation).

We don't ferment wine musts or sugar washes without nutrients for the yeast, because we know we end up with stalled ferments, where the yeast konks out waaaay before the end of fermentation, often at stupidly low numbers. These guys perhaps didn't know much better, but they set the yeast off on the back foot, and then abused them down the line, and made (and wrote) a scientific paper with the results. I don't think we should take it for what it is on a homebrew scale to begin with, and considering the article didn't once mention that the yeast cells die (I only ever saw mentioning of "fermentation stopping", not "yeast cells dying"), I don't think we should advocate that the alcohol will kill the yeast.

Because I'm still not of the opinion that it does. And yes, I've done step-feeding on yeast before in a mead, and it got to 19% ABV (from what I could calculate) before fermentation stopped. I cold crashed the mead and stood it aside to fine. One jar was sealed and stored in the pantry for almost 2 years, before the mead was consumed (it was stupidly sweet and incredibly nice to drink, by the way, like sherry or port).

At the bottom of the jar was a thin layer of sediment. I added some water and honey, and while the resulting fermentation was filled with flaws - it fermented. Yeast did not die.
 

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