How to calc ABV if you add more sugar

Okay, so Ive read some recipes where you add additional sugars i.e. brown sugar, maple syrup, molasses... to the primary after so many days of fermentation. My question is how in the world do your figure out your ABV if your gravity readings are always changing?? Do you take a reading every time you add sugar? Is there a magic equation that I haven't read yet?
Thanks!

Yes there is a measurable amount of fermentable sugars to each item. i.e. cane sugar = 42 GU per lb. in a 5 gallon batch you divide the 42 by 5 = 8.4 = add 1.0084 to your OG.

Is there a easier way to find the gravity unit of fermentable sugars for a noob??

Thanks

sandman24 said:

Is there a easier way to find the gravity unit of fermentable sugars for a noob??

Thanks

Click to expand...

By looking at this table and going by the third (or fourth) column:

http://www.howtobrew.com/section2/chapter12-4-1.html

http://www.northernbrewer.com/sugars.html also lists a couple, and brewing software such as Strangebrew Java 2.01 has a database of all sorts of ingredients that you can look up, add to a recipe, and calculate the resulting gravity.

By far the easiest way is to enter this data into a brewing program like Beer Smith. Refined sugars have totally consistent and known fermentability, so its predictions will be very accurate for something like this.

Adding sugar is different to the original mash, where the software estimate can be thrown off by differences in your mash efficiency. But as long as you take a reading after the initial mash and boil, you can use that to calculate your efficiency and get the software set up right, after which it will accurately tell you the effect of adding extra sugars.