How to calculate OG additions from fruit?

So I started a Raspberry Melomel from https://www.homebrewtalk.com/f80/raspberry-melamel-bronze-medal-winner-2010-great-arizona-homebrew-competition-183027/ which I measured at 1.110 prior to pitching the yeast.

Is there a formula for calculating the sugar increase from fruit usage during primary or secondary fermentation? Without fruit this should end up at 13.3% ABV but I'd like to know what to expect from the fruit so I have a semi realistic ABV.

I think there's a calculator for doing this on got mead, since it's dependent on the fruit.

Jukas said:

Is there a formula for calculating the sugar increase from fruit usage during primary or secondary fermentation? Without fruit this should end up at 13.3% ABV but I'd like to know what to expect from the fruit so I have a semi realistic ABV.

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I believe the raspberries would lower your gravity, not raise it. Jukas is measuring the liquid at 1.110. Raspberries contain additional sugar, but they also contain juice. Raspberries have a SG somewhere around 1.022. Wouldn't you expect adding 1.022 juice to lower the gravity of a 1.110 mead?

I like the GotMead calculator. That calculator raises the OG when making fruit additions, but you have to include the fruit volume in the calcs. Making a 5 gallon batch containing 20 lbs of raspberries is different than adding 20 lbs of raspberries to a 5 gallon batch.

GinKings said:

I believe the raspberries would lower your gravity, not raise it. Jukas is measuring the liquid at 1.110. Raspberries contain additional sugar, but they also contain juice. Raspberries have a SG somewhere around 1.022. Wouldn't adding 1.022 juice lower the gravity of a 1.110 mead?

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Perhaps someone more knowledgeable could step in, however I think your logic is flawed since we're talking about adding the raspberries during the initial fermentation process because there is no alcohol yet, only ferment able sugars.

At this point we're still talking about the addition of fermentable sugar, not the blending of already fermented meads, or dilution to a fermented mead.

GinKings said:

I like the GotMead calculator. That calculator raises the OG when making fruit additions, but you have to include the fruit volume in the calcs. Making a 5 gallon batch containing 20 lbs of raspberries is different than adding 20 lbs of raspberries to a 5 gallon batch.

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Got a link to the calc? I looked at the GotMead site and couldn't find a tool for calculating gravity from fruit additions.

http://www.gotmead.com/index.php?option=com_content&task=view&id=745&Itemid=16

That is the link to the calculator. As long as the total volume of the must = for example 5gal with the fruit already added and not 5 gallons of honey/water plus the pounds of fruit then the calculations should be close. That way the volume is calculated in with the must.

Jukas said:

Perhaps someone more knowledgeable could step in, however I think your logic is flawed since we're talking about adding the raspberries during the initial fermentation process because there is no alcohol yet, only ferment able sugars.

At this point we're still talking about the addition of fermentable sugar, not the blending of already fermented meads, or dilution to a fermented mead.

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GinKings was correct, at least to the extent that any of these formulas are correct. The assumption is that you have a solution of sugar and water, so any increased gravity is due to sugar. This is closest to being true at the start[*]; once you ferment, there's alcohol in as well, which introduces a small error since it is less dense than water. In any case, you won't go very wrong just by performing a weighted average of the gravities.

If you're adding a juice that is less sugar per volume than your must, it will reduce the potential ABV. The additional sugar will give you more alcohol, but it will give you more non-alcohol as well.


[*] For mead, anyway. In the case that you have other ingredients that are not 100% fermentable, there's probably a period when there's just enough alcohol to compensate for non-fermentables, making the apparent gravity exactly correct for calculating potential alcohol... but this is a stupid math trick, not actually a useful concept.

The Mad Fermentationist covered this topic, hopefully this will help:

http://www.themadfermentationist.com/2010/10/adding-fruit-to-beer-increases-alcohol.html

Once you're drinking something over 10% ABV, does it really matter much a percent here or there exactly what the ABV is? It's all an estimate anyway...

zeg said:

The additional sugar will give you more alcohol, but it will give you more non-alcohol as well.

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Thanks, that was the part I obviously overlooked, the % of water contained in the fruit.

Machalel said:

The Mad Fermentationist covered this topic, hopefully this will help:

http://www.themadfermentationist.com/2010/10/adding-fruit-to-beer-increases-alcohol.html

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Thanks for the link, I bookmarked his site for further reading.

biochemedic said:

Once you're drinking something over 10% ABV, does it really matter much a percent here or there exactly what the ABV is? It's all an estimate anyway...

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In practical terms it doesn't matter a bit, in academic terms it's always nice to be as close to spot on as possible.