Rough guess - how much strength would 1kg of frozen fruit have added?

[Toastkid]

I'm doing one of my standard brews. OG was 1064. When the fermentation had slowed down, I decided to add 500g of frozen pineapple and 500g of frozen mango. I defrosted them and put them in the blender, so it was a big load of pulp, then poured that into a section of tights (my standard dry hopping equipment) and dropped it into the brew, weighted down.

What I should have done perhaps was to take the gravity reading before putting it in, and a while after, but I didn't. Without the 1kg fruit addition it would have ended up around 6.5%. Does anyone have a rough guess of how much extra strength the 1kg of pureed pineapple and mango would add to it?

 

[Agentgonzo]

Take a look on the internet for sugar content by weight of the fruits. That should give you how much sugar you added from the 1kg of fruit

Then treat that as just a sugar addition

 

[Toastkid]

Take a look on the internet for sugar content by weight of the fruits. That should give you how much sugar you added from the 1kg of fruit

Then treat that as just a sugar addition

good idea thanks! According to a couple of sources it looks like the sugar content is about 10% of the total weight (which is surprising, i thought it would be higher). So that's 100g of sugar effectively.

According to some other places, 100g of sugar will convert to 61g of ethanol (ie pure alcohol). If we go with 20 litres total volume for the sake of argument, that is roughly 20,000 grams of liquid. So, to get the proportion of alcohol from that 61g it's 61/20000, which is 0.00305, or 0.3%.

So, the sugar from the fruit will (according to that maths) increase the total alcohol by 0.3%.

The brew started at 1.064 and I usually keg it at 1.014, so that would normally be 6.6% alcohol. So the fruit addition will increase that to 6.9%.

That all feels sort of reasonable.... thanks!