Partial Mash questions

[ribbityrob]

I am attempting my first partial mash brew tomorrow. I have done 4 extract batches with steeping grains and all have turned out great. I still have to do a partial boil due to my current equipment and have some questions about pre boil gravity readings with a concentrated boil. I have already figured how much grain, extract, water and sparge water to use.

1. How can i get the proper pre boil gravity reading in a concentrated boil? I want to know how much extract to use based on the gravity of the wort i get from the mini mash.

2. Is it necessary for me to take a pre boil gravity for this?

The only thing i thought of was to use a sample of the mini mash wort and dilute it with the same amount of water to take a hydrometer reading, since thats what i am doing to the batch. Im not sure if that will work or not but it made sense to me. Any help would be appreciated. Thanks!

[brewinhard]

I wouldn't worry too much about a pre-boil gravity for your first partial mash. I do understand that you probably want to nail it the first time around though. I would just enjoy the new process you are embarking on and look forward to the quality of your beer to sky rocket! Do be sure to mix your "top off" water in well with your chilled concentrated wort as gravity readings can get screwed up if you do not mix it well enough (ie too low of OG). By the way, what are you brewing up?

[ApresSkiBrewer]

This is what I would recommend (homebrew style calculations, working with total GU's)

1. Take your target OG, subtract 1, and multiply it by 1000 (This get's you to GU's). Then multiply that by however many gallons you want to have at end of boil - or in your case, in the fermentor since you are still doing a concentrated boil. (5 gal, 5.5 gal, 6 gal, whatever) This will give you your total GU's - Gravity Units. (example. Target is 1.050 at 6 gallons in the fermentor. = 50 x 6 = 300 target total GU's).
2. After your mini mash, take an OG. Multiply it by the volume of wort you've collected. ( ex. 1.040 and collected 3 gal. = 40 x 3 = 120 GU's)
3. Subtract the GU's from your mini mash from your total target GU's. (ex. following the example 300-120 = 180)
4. Use whatever extract you've got to fill in the remainder GU's needed. (ex. DME light will give you roughly 40 PPPG (points per pound per gallon), so divide the remainder by 40 if using DME, 180/40 = 4.5 pounds)
5. Add that amount of DME or preferred extract to your partial boil, chill, and dilute into the fermentor to your target volume. Voila.

That should get you close enough.

Key is to think in terms of total GU's at your target volume, which you'll adjust to right at the end of your brew day in the fermentor. Make sure your Total GU's add up to what you want in your kettle, and don't sweat it. You don't even have to worry about evaporation rate or anything, if you do it in this manner, because you'll dilute to a set volume in your fermentor, that will correct any of those possible issues.

Cheers,

[ribbityrob]

Thanks for the answer! I'll do those calculations next time. I brewed the Pale w caramel from BCS. I used magnum for bittering, chinook and centennial for flavor and aroma. I mashed 5 lbs American 2 row .75 munich and .75 C40. I added 3 lbs light LME before boil. It went well, my OG ended up 1.051, I was shooting for 1.052 so i was pretty pumped. I didnt shake the fermentor to mix it up but i use a pretty long wine theif and havent had any issues with an off reading yet. I pour my wort on top of the dilute water which was pre boiled the night before. I feel like it mixes fairly well. Cant wait to see the difference between this batch and the same recipe with all extract and steeping grains. Thanks again.