Calculating Remaining Sugars

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drbugga

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Hi Brew Buds

This is my second batch ever (with store bought juice) and I thought I might want to get a little more precise in terms of calculations.

I have my initial and an interim SG 7 days later. IG: 1.048 and 7 Day is 1.008 which gives me roughly 4.9 ABV. What I want to know is how much sugar was consumed in the last 7 days. I know my store bought sugar content. Is there a way to calculate that or a calculator that can give me that info? I did a taste test and my tongue tells me that there is no sugar but the fermentation is in full swing (co2 bubbles in airlock) so my taste buds are wrong.

I initially thought that I can back calculate using priming sugar calculator but that requires co2 vol as an input.

TIA
 
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Depending on what you mean by "sugar", I think you will find that the story is a little more complex than the Vinolab approach, which I find to be a good source of calculators.

I believe that in the Vinolab calculator, "sugar" figure is actually "total solids", i.e. fermentable sugar plus non-fermentable sugars, acids, tannin, etc, etc, which all contribute to the SG of the juice.

In general terms, juice comprises 80% water and 20% total solids, with 80% of the solids being fermentable sugar (i.e. what we usually think of as the sweet stuff), the rest being non-fermentables. The amount of non-fermentables remains constant during fermentation whereas the sugar gets consumed into alcohol and C02. So, even when fully fermented some juice can have some sweetness because of substances like glycerin and sorbitol and un-sweetness because of acids and tannins.

Store bought drinking juice typically has about 3-4g/L of malic acid, but it can be higher. The ideal acid level for cider is generally in the range 5-7g/L, so the acid in your juice may well offset your taste buds' perception of sweetness if there is little sugar left to ferment.

As an example, sweet apples like Fuji apples can have around 4g/L of malic acid and 8g/L of sorbitol. Even though sorbitol is only half as sweet as fructose, when fully fermented the cider still has a touch of sweetness. Most other apples have in the order of 4 g/L of sorbitol and similar levels of malic acid so the perception of residual sweetness in the fully fermented cider would be reduced.

I have only come across a couple of sources that break the total solids into fermentable sugar and non-fermentables These are Claude Jolicoeur's Table 8.8 and Proulx & Nichols p47. There may however be others. In both of these, for your initial SG 1.048 the fermentable sugar is 102g/L compared with the Vinolab figure of "total solids" of 125g/L.

Only the P&N table has a sugar figure for SG 1.008 at 15.5 g/L, which is the equivalent of about 1/2 teaspoon of sugar in a cup of coffee. What would adding 1/4 teaspoon of malic acid (about 5g/L) do to the taste of the same cup of coffee? I don't know but I don't think it would be as sweet any more!

So, you may need to review your taste buds' perception of sweetness in the light of the offsetting effect of the residual malic acid and tannin.

Sorry, this isn't the perfect answer, but I hope it helps with your dilemma.
 
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