Extra Alcohol with fruit... how do I measure?

My brother and I've brewing for a while now, and some of our most aclaimmed beers are the ones with fruit, specially our raspberry porter. We use real fruit,actually, we make a puree, and add it after the first fermentation, but then the yeast starts working again and the fruit ferment. My question is how can we measure that extra % of alcohol and how control it. Cheers

If you use beersmith, there is an additional download that will give you info on fruit that you can add to your recipe. It adjusts it as fermentable, and shouldnt matter if it is before primary or not...

heres the link

http://www.beersmith.com/beersmith-1-4-support/

Look up the nutrition facts on the fruit in question. You'll be able to figure out how much sugar you're adding to your beer. It's usually given as grams of sugar per serving and another item will be the serving size. So you can calculate the total amount of sugar going into your beer. Virtually all the sugar in fruit is fermentable.

Remember that the fruit puree contains a substantial amount of water, so you may not be increasing the ABV at all.

The more you know, the more accurately you can figure out the additions.
You need to know the volume of resultant juice (minus pulp) as well as the gravity of the juice. Then you can just figure out:

(OG1 * Vol1 + OG2 * Vol2) / (Vol1 + Vol2)

I'd imagine this is less accurate when Vol1 and Vol2 are not very close, but I'll be using this to figure out the addition of 1 gallon of cider. BS2 doesn't seem to be able to add sugary liquids without changing it to sugar (dry) and adjusting the total volume - what a hack that is.

If you're not adding significantly to the volume, it may be easier to figure out your total sugar and adjust your volume in BeerSmith.

An easy way to control the production of alcohol from fruit fermentation is to throw a campden tablet in there when you want to slow things up. Thats what ive done. Kind of weird since i usually only use it for my mead but works all the same.

underground and under the influence