Combine Multiple Starting Gravities

[noggins]

So I guess this is a beginner's question, although I couldn't find an answer for it anywhere on the forum...

Gonna be brewin up some hard lemonade this weekend from a recipe I combined from other recipes I've found(recipe to follow). The main question is, how can I calculate starting gravity using two different sources that will be combined? Can I just take the OG of the first wort and add it to the OG of the second wort? I assume there's gonna be some math involved, should I wait and come back to post when I have the actual gravity reading to figure it out then?

Thanks for any help, here's the recipe:

Hard Lemonade
------------------
4lb sugar
2 gallons apple juice
4 cans frozen lemonade concentrate
4 cans frozen pink lemonade concentrate
4 cans frozen limeade concentrate
EC-1118 or wine Yeast
3 Gallons Water
-------------------
Dissolve 1lb sugar in apple juice and pitch yeast.
Once fermentation begins, mix concentrate with remaining sugar & water and rack into primary.
Ferment until stable.

 

[bgruis]

If I understand you correctly.....what you will want to do is use a program like BeerSmith or Promash to build a new comined recipe and this will give you an accurate OG.

 

[Russtang]

I'm no expert, but it seems like the sugar and apple juice mixture in the first step are like a yeast starter. Shouldn't take more than 20 or 30 minutes for fermentation to begin. There should be no appreciable gravity change if you mix it with the concentrate as soon as fermentation begins.

I would follow directions and take an OG reading once everything is mixed in the primary. Should be very close to the actual initial OG of everything.

 

[dcp27]

(OG 1 * volume 1 + OG 2 * Volume 2) / (Volume 1 + Volume 2)

 

[noggins]

all good answers, while I'm on the topic, would just pouring the bunch of lemonade from the second wort into the primary with the first wort cause any real damage or should I rack it in just to be safe?

 

[noggins]

In case anyone is curious, here's the gravity readings I got:

2 Gallons Apple Juice & 1lb Sugar OG:1.075
3.5 Gallons Lemonade & 4lb Sugar OG: 1.120
5 Gallon Wort OG: 1.113

The final OG was taken just after adding the lemonade to the mix, about 8 hours after pitching yeast.