Calculating O.G. beforehand?

Is there a good reference site, or set of formulae, that can be used to calculate O.G. before you make a wine/cider?

As of right now, I have been making apple wine/cider using pure juice and yeast, but want to make some batches using other fermentables as well. Is there a way I can calculate the original gravity other than just trial and error?

Eric

Depends on the fermentables. The value for brewing grains are known and readily available. It sounds like you are using juices. Unless you know (Or can measure with a hydrometer/refractometer) the amount of sugar in them then there is no way to calculate in advance.

GT

I do have a hydrometer and know how to use it, but I guess I asked the question wrong (DOH!)

Let's say I'm making 6 gal. of cider, and the straight apple juice has an O.G. of 1.052. I'd like to know if there is a way to figure out, "OK, I need X amount of AJ concentrate/honey/dme/etc. to raise the gravity to 1.080, or 1.090, or 1.100, etc....."

If I can do a few simple equations, that would be great! I'd like to avoid adding and checking, adding and checking......

Eric

You need the extract potential of the "AJ concentrate/honey/dme/etc."
Table sugar and DME yield 46 points per lb/gal (ppg)
Corn sugar yields 42 ppg
LME yields 37 ppg
Honey yields 35 ppg
Maple Syrup yields 31 ppg
So if you start with 6 gal at 1.052 (that's 52 points) and you want to use corn sugar to raise the gravity up to 1.080, you need to add 80 - 52 = 28 points for each gallon.
28 points * 6 gal = 168 points.
168 / 46 = 4 lbs
So adding 4 lbs corn sugar to 6 gal at 1.052 would raise the gravity to 1.080.
This is not entirely accurate, because adding the "AJ" will also increase the volume a small amount, but it is fairly close providing "AJ" does not have a very low extract potential.
If you don't know and can't find the extract potential of your addition, you can dissolve a small amount in water, cool it to 60F and take a gravity reading. Some simple math should tell you what the extract potential is, providing your weight, SG and volume measurements are accurate.

-a.