A few questions on how using different sugar sources affects the final alcohol content

[thisissami]

Hi All,

Everything I've seen around calculating the alcohol content that you end up with at the end of a ferment revolves around the Original and Final specific gravities that you measure. However, it seems odd to me that this is all that would be involved in that. For example, I imagine that a pure white sugar would almost entirely ferment to alcohol (+ CO2), whereas honey would have additional molecules that remain in the liquid.

Does anybody have a better understanding of how different sugars affect the fermentation process / specific gravities / final alcohol percentage? My sense is that there's some slight variations across different sugar types. If that is indeed the case - does anybody know of any resources that define how different sugars affect the final outcome? For example, I'm imagining a table that would have various sugar types, and share how much % alcohol you would generally end up with if you fully fermented 100g of said sugar source into 1L of water.

I've been making a variety of alcohols with honey and cane sugar (separate ferments; I've never mixed both, nor do I intend to) - and I'd like to get more accurate with my creations. If there is any info on this stuff that I could use, I'd find that most helpful!

Cheers - thanks for giving this a read. I hope you're all having a lovely day!

 

[bernardsmith]

Hi thisisami, I wonder if perhaps I am misunderstanding your post or you are misunderstanding how we use an hydrometer to measure the density of a liquid and so determine the amount of alcohol in a mead or wine. Note my wording: an hydrometer does not measure alcohol or measure fermentable sugar. It measures the DENSITY of a liquid and the assumption is that when you make a wine the only thing affecting the density of the water is sugar. (if you were measuring the density of ocean water the assumption would be that the key variable is salt; and if you were measuring the density of your car radiator fluid using an hydrometer the key variable would be the amount of anti-freeze dissolved in the water). An hydrometer measures DENSITY (AKA specific gravity)

Let's ignore the type of fermentable - whether honey, table sugar, malted grains or fruit juice. You have a liquid with dissolved sugars from one or more of these sources of fermentable sugar and you take a sample and measure the density (gravity) and the first reading is 1.090 (you would need more honey (by weight) to obtain that same reading than if you were using say, table sugar and you were making a wine or mead from , say elderflowers (no sugars in the flower) or raspberries (there would be sugars in the fruit).

You pitch the yeast and whatever other additives (nutrients, acids, tannins etc) and after say, two weeks you measure the gravity again. This time the gravity is 1.010. Is this the FINAL gravity? I don't know but TODAY it is 1.010 and that tells me that 80 points (1.090 minus 1.010) of sugar have been converted to alcohol and carbon dioxide. Eighty points of sugar have been fermented and if I use the formula to calculate the amount of alcohol in the mead or wine (.080 * 131) I know that the mead or wine has TODAY 10.5% alcohol by volume. Doesn't matter if the sugar was honey or fruit juice or table sugar or malted grains - the alcoholic content is 10.5% by volume. If over the next week the gravity of the wine continues to drop to say 1.000 then there is another 10 points of sugar that has been fermented and that would suggest that the wine or mead is now at about 12%
Are there unfermentables in the solution? No question - the density (gravity) of water is 1.000 . and that is a conventional number. It is what we say pure water is and all other liquids are measured using water as the base line. The gravity of pure ethanol (alcohol) is .815 and you are never going to get even close to that reading with fermentation (even distillation will not remove 100% of water) but for all intents and purposes you can simply take a first reading when you make the solution to be fermented , take a second reading when you think active fermentation should be over and you subtract the second from the first and multiply the answer by (as a rule of thumb) 131 to obtain the amount of alcohol in the liquid you have. Doesn't really matter what else might not have fermented (as long as there is nothing gaseous or solid in the solution you are measuring to affect the buoyancy of the hydrometer and so give you an incorrect reading of the density of the liquid.

Does that help? Are we both now on the same page? Or is there something different that you are asking about?

 

[thisissami]

Does that help? Are we both now on the same page? Or is there something different that you are asking about?

Hi @bernardsmith - yup, that actually really helps! I did understand that it's the liquid's density that we're measuring. The part that was escaping my mind was the "it really doesn't matter if there's other minerals/nutrients/etc in addition to water/sugar/alcohol, because we're just measuring the difference between the start/finish - which will show the change from sugar to alcohol". That helped things click for me, so thank you!

So I guess the question that I really want to ask then is: is there any kind of equivalency factor between different types of sugar? Like... 100g of honey tends to equate to 90g of cane sugar and 80g of white sugar (in terms of how much sugar molecules you end up with that will convert to alcohol). Or is it more of a "you just gotta experiment and figure it out on your own" type thing.

 

[bernardsmith]

Basically, the fermentable sugars used in wine making are glucose, sucrose, and fructose. In brewing (beer) you have maltose. Honey is made up of the first three but there is also some water in honey - not much but enough such that a pound of honey is going to have enough water to mean that when you add 1 lb of honey to water and raise the VOLUME of the water with that amount of honey to 1 US gallon the specific gravity of that water and honey solution is likely to be around 1.035. If you took 1 lb of table sugar (sucrose) and added that to the water to make 1 US gallon the SG of that solution is likely to be about 1.045. Both will ferment to give the same amount of alcohol based on the sugar content so that pound of honey has a potential ABV of .035 * 131 = 4.5% ABV, whereas the sugar you added has a potential ABV of .045 * 131 = 6% ABV. There are differences in different kinds of sugar but I guess I use table sugar and honey and when I ferment fruit I measure the gravity of the juice but generally assume that it will be in the ballpark of about 1.045 - 1.055 when pressed or expressed from the fruit.

For all intents and purposes juices and honey and simple sugars are 100 % fermentable. That's not the case with grains. With grains you have a significant amount of complex sugars that the yeast you pitch cannot ferment so beers tend to finish sweet (around 1.010 - 1.015) But you expect a wine to finish brut dry (below 1.000) and either the fruit finishes with a perception of sweetness although it is absolutely dry or you can stabilize the wine and add sweetner.