Accounting for fruit contribution to alcohol level

[rbowers]

For my upcoming raspberry wheat recipe I plan to secondary the beer on top of a raspberry puree for 2-3 weeks.  Likely going to use 3lbs.  Is there a way (or a reason) to account for the fermentation of raspberry sugars contribution to the alcohol level or is it negligible?

[mtnrockhopper]

It would require math.

Fruit contributes both sugars and volume too complicate that. I think it is often a wash.

[tschmidlin]

You can take a small amount of the puree and mix it with a measured amount of water, take the OG and then calculate the OG of the puree itself.  From there you can calculate what the new OG of the beer will be.

[nateo]

It would require math.

Fruit contributes both sugars and volume too complicate that. I think it is often a wash.

I would bet fruit would usually lower the alcohol, since fruit is mostly water with a bit of sugar.

[bonjour]

Beer Smith has a grain addition of fruit based on the US average brix (% sugar, ) of the fruit.

Bottom line, unless your wort is pushing 100% fruit very little impact

Raspberries have an average potential of 5 pppg so you are adding 3lbs* 5 pppg = 15 gravity points, so for the same volume in a 5 gallon batch your OG will go up 15/5 = .003,  This will increase abv by about .4%abv

[kylekohlmorgen]

I am doing the same thing now with blackberries, so this is helpful information!

The volume of the puree is important to account for. If you're going from a 6.5 gal carboy to a 5 gal, make sure you have enough room for the fruit and a bit of headspace for another (albeit small) fermentation. I used fermcap-S because the 3068 I used can be a very foamy fermenter!