Ajout de fruits et alcool / Fruit addition and alcohol

*** English Below ***

Bonjour à tous!

J’ai brassé la semaine dernière ma première Milkshake IPA, et c’est aussi la première bière dans laquelle j’ajoute des fruits en fin de fermentation.
J’ai donc ajouté 2kg (4,4Lbs) de purée d’ananas hier soir dans mon fermenteur, plus 2 gousses de vanille (que j’ai laissé infuser au préalable dans de la Vodka) et mon houblon.
J’ai juste une simple question par rapport au sucre contenu dans l’ananas qui va être converti en alcool (ou d’autres fruits en général), est-ce qu’il y a un moyen de calculer l’alcool que ça va rajouter, ou c’est vraiment négligeable?


Hello everyone!

I brewed my first Milkshake IPA last week, and it’s also the first beer I’ve added fruit to at the end of fermentation.
I added 2kg (4.4Lbs) of pineapple puree last night to my fermenter, plus 2 vanilla beans (that I let steep in vodka beforehand) and my hops.
I just have a simple question about the sugar in the pineapple that is going to be converted to alcohol (or other fruits in general), is there any way to calculate how much alcohol it will add, or is it really negligible?

Thank you!

I don’t have experience with this personally but this article from BYO has an equation you can use. Assuming it’s a 5 gal batch…

(4.4 × (13 ÷ 100) × 45) ÷ 5 = ~5 gravity points.

The alcohol could go up or down. You are adding water from the fruit too. There are a few sources where you can find the standard gravity (sg) of the fruit and calculate the alcohol content if its completely fermented and take a weighted average of the two.
There are equations for this are in “American Sour beer” (i don’t have it with me) but here is the author’s rant of the subject.

Here is his calculation:
Effective Brix/Plato = (Weight of beer x Brix/Plato of beer + Weight of fruit x Brix/Plato of fruit) / (Weight of beer + Weight of fruit)

For example if you have 4.5 gallons of 11 P (1.044) beer it would be 1.044 x 4.5 x 8.35 = 39.2 lbs of beer onto 10 lbs of 14 P cherries, the effective OG would be (39.2 x 11 + 10 x 14)/(39.2 + 10) = 11.61 P. That is to say the increase in the effective starting gravity was .61 P, enough to boost the alcohol by .3% ABV assuming the same FG (about the same increase in alcohol from the priming sugar).

Thanks a lot Marc and Albert, I’ll test those 2 methods to see the difference :wink:
Also, if my beer is good, I’ll share the recipe later!

Here is the method I figured out when I added frozen mango to my last batch. I looked at the nutrition label on the package, it 13.6 % sugar content. I used 1.25 kg mango, so that was like adding 0.17 kg white sugar and 1.08 kg water to my batch. Note though that I added this to the primary and measured the
OG and volume before pitching the yeast.

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Like others here, I always assumed the boost to alcohol (if any) was negligible due to the water add.

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