how do i calculate what my pre-boil gravity should be?

Planning my second partial mash. On my first one I had a very low gravity reading right before i pitched my yeast. I didn't take a pre-boil gravity reading but i regret it because I think i had very low efficiency which resulted in low SG.

So... how can I calculate what my preboil gravity is supposed to be so I can adjust my extract additions if need be?

get beersmith its free for 20 days. You can input your recipe and it will calculate everything for you! Then use your hydrometer and measure your preboil gravity and match it up with beersmith..

hey how convenient, i'm on day 18 of my free trial. Where do I find out what the preboil gravity is using BeerSmith?

+1 on Beersmith and the free trial. I'm sure there are a couple websites with free calculators as well if you google for it.

Just keep a little DME on hand to bump up if you have a bad efficiency.

Biggest misses on efficiency are probably bad crush on the grain, improper temperature realization or maintenance, improper water amount, and improper stirring of the mash to distribute temperature.

I flubbed my efficiency first partial mash, but had documented everything. On my next one (all grain) I saw a very good improvement by reviewing my notes and adjusting for my previous errors.

So i found the Brewhouse Efficiency button in Beer Smith.

This window popped up:


So is 1.095 my preboil gravity? Do I take a reading when my first and second runnings are in my brewpot and I have collected my 3.25 gallons? Or is it just the gravity reading of my first runnings?

Are you doing 3 gallon boils or full boils?

Looks like 3 gallon boils w/water addition to make 5 g?

First and second runnings into brewpot. Stir thoroughly. Adjust for temperature (that's in the tools section of BeerSmith too).

the wort OG will be considerably higher than style OG until you add your top-off water. (like 1.095).

recommendation: splurge for a 8-10 g brewpot for full boils as soon as feasible. I promise you won't regret it.

Yes right now i've got a 4 Gal brew pot so about 3.25 G boils. Then I top up with water in the fermenter.

Question about the 1.095. Does that include the gravity points from the LME? I think it might. The recipe is a partial mash so i've got 6 lbs of grain and 5 # of LME as a late addition.

Would it work if I removed the lme from the recipe, adjust my batch size to my boil size and look at my expected OG? I can't try it right now because i'm at work and BeerSmith is at home.

In beersmith it is listed on your brewsheet. When you are looking at a recipe at the top click on "Preview BrewSheet" and it will be listed on there

pre-boil gravity = (post-boil gravity)*(post-boil volume)/(pre-boil volume)

(for the calculation, use everything after the decimal point for the gravities; ie. 1.050 = 50; 1.105 = 105)

beersmith is great, but you don't need it for something this simple.

Is this math based on actual (hot) or room temp wort volume?

It looks like if you do the math hot to hot, or room temp to room temp, it works out the same.