SG (or brix) of sucrose vs fructose vs glucose

[rhodesengr]

Maybe this should be in the Mead section but I want to make sure I understand how to setup up a must based on something other than fruit juice. I've mentioned before that many years ago I made Mead with simply honey. Now that I am all set up from my plum wine making efforts, I want to make something else. Because I really love tequila, it seems like making a wine (or mead) from Agave nectar would be really cool. Costco sells agave nectar at a reasonable price.

In reading up on Agave vs other forms of sugar, I see that Agave is primarily Fructose and Glucose. I never asked about this when setting up my plum must. I have no idea what forms of sugar are in my plums but I added sucrose to bring the SG up to near 1.100 before fermenting. With Honey or Agave I would just be adding water to get an appropriate starting SG. Looks like Honey might be mostly Fructose also.

So here is my question. Is the SG scale on my hydrometer (and/or refractometer) the same for all forms of sugar or do I need to compensate if the it's mostly fructose vs sucrose? Asked another way, is the alcohol potential the same for the different forms of sugar?

 

[Hazelemere]

Maybe this should be in the Mead section but I want to make sure I understand how to setup up a must based on something other than fruit juice. I've mentioned before that many years ago I made Mead with simply honey. Now that I am all set up from my plum wine making efforts, I want to make something else. Because I really love tequila, it seems like making a wine (or mead) from Agave nectar would be really cool. Costco sells agave nectar at a reasonable price.

In reading up on Agave vs other forms of sugar, I see that Agave is primarily Fructose and Glucose. I never asked about this when setting up my plum must. I have no idea what forms of sugar are in my plums but I added sucrose to bring the SG up to near 1.100 before fermenting. With Honey or Agave I would just be adding water to get an appropriate starting SG. Looks like Honey might be mostly Fructose also.

So here is my question. Is the SG scale on my hydrometer (and/or refractometer) the same for all forms of sugar or do I need to compensate if the it's mostly fructose vs sucrose? Asked another way, is the alcohol potential the same for the different forms of sugar?

same for fructose, glucose and sucrose (cane sugar)

 

[Snafflebit]

It is an interesting question.

Sucrose is a carbohydrate composed of one glucose molecule and one fructose molecule. Glucose and Fructose have the same weight because they are composed of the same atoms C6-H12-O6, but the molecules have a different shape.

Brix, in terms of winemaking, is a way of expressing percentage of sucrose. So I'd say if you are trying to measure concentration of other types of sugar, Brix is the wrong way to do it.
Using specific gravity is what I would do, and fructose-glucose ratios that vary from 50/50 will not affect SG.

So trying to use honey as a fermentation sugar in a fruit wine or if you were trying to add table sugar to a juice that was not a 50/50 ratio of glucose fructose, the math could get messy for Brix, but SG would be fine.

I did a search that says honey is about 40% fructose 30% glucose and 17% water, so not an even ratio.

I bet some expert mead makers could answer this question better.

 

[winemaker81]

Using specific gravity is what I would do

Same here. SG provides a sufficiently accurate reading for my purposes.

 

[Rice_Guy]

@Snafflebit has some good points.
The hydrometer is measuring the quantity of material in a solution. To make it simple this is like saying how many grams of sugar or salt or acid is in the must. For your question of will sucrose have the same grams of fermentable as sucrose or glucose. YES, , ,

BUT the reading is also including salts and non-fermentable carbohydrates. Therefore if we run a lab test for reducing sugar it will be off a bit from year to year and from apples to grapes to several honeys to agave. We live with it, The error is in the range of 1 to 2%. AND It is not practical to do a permanganate reduction in your kitchen, ,,, but there are some enzymatic glucose tests so potentially we could do a more accurate more expensive reading.

To complicate the problem honey has higher molecular weight sugars that yeast can’t digest and pears have sorbate which yeast can’t digest (sorbate is a no calorie industrial sweetener too) and birch trees have xylose etc etc.

Basically a hydrometer is an $8 tool which we can use forever (my best one was Mom’s). It is not realistic to spend $100 per sample to have actual % weight numbers of each sugar.

Yeast do not have the same preference for each sugar. Once you get to 14% ABV they will become less efficient metabolizing fructose. Yeast really really really like glucose (corn sugar). So another variable is the finished ABV and the strain of yeast.
This is getting muddy, ignore the 1% of your estimated ABV error, taste matters more.

 

[rhodesengr]

the math could get messy for Brix, but SG would be fine.

Thanks for the reply. See from my perspective (which is a guy looking at his hydrometer), the relationship between Brix and SG is fixed. They are just different scales printed in the piece of paper inside my hydrometer. So from my perspective, they are interchangeable. That is kind of why I posed the question in different ways including alcohol potential. If the AP was drastically different for different sugars, one might end up with too much or too little alcohol if compensation was needed but not applied.

 

[rhodesengr]

I get that a hydrometer doesn't know what it's measuring. Kind of why I am asking this. I used to have one for measuring battery acid. Sounds like we'd just use the same set up regardless of sugar type. Thanks guys. Better to ask and be sure.

 

[winemaker81]

Thanks for the reply. See from my perspective (which is a guy looking at his hydrometer), the relationship between Brix and SG is fixed. They are just different scales printed in the piece of paper inside my hydrometer. So from my perspective, they are interchangeable. That is kind of why I posed the question in different ways including alcohol potential. If the AP was drastically different for different sugars, one might end up with too much or too little alcohol if compensation was needed but not applied.

Your question is a good one, even if the answer is not all that exciting.

Wine (and beer) making contains a bunch of approximations. ABV is the best example -- at least 3 different equations are required to calculate ABV, and all are approximations because the sugar-->alcohol translation is not a steady curve. Making it weirder, the answer influences which equation should be used, as different equations are required for beer, wine, and strong wines. The equation for beer (~3-8% ABV) doesn't work for table wine (~10-15%) or stronger wines (~15+%). [The ranges I listed are for illustration; I did not locate any firm answers that I trusted.]

I've done some research in this area, but realized that getting approximate answers easily makes more sense than putting in a lot of effort and still being unsure of the answer. At this point it's best to simply pour a glass of wine.