Boil Off (Partial Boil)

[JJ86]

I may be about to ask a very obvious question, but here it goes..

I am an extract brewer and my setup only allows for me to do a partial boil (4 gal pot). I have been working to determine my boil off rate (.85gal/hr) and now that I have it I am curious to understand how this actually effects a partial boil. Since I am already topping off my primary with approximately 2 gallons of water, does it really matter if I account for boil off during my boil? I'm sure it does, but was hoping someone could explain how maintaining a higher volume during the boil allows for a better outcome when topping of to 5gallons.

 

[TipsyDragon]

as long as you hit your pre-boil gravity the size of the boil for the most part doesn't really matter. pre-boil and the subsequent boil gravity affects hop utilization. the lower the boil-gravity increases hop utilization and you need less to get a target IBU. higher boil-gravity decreases utilization and you need more hops to get a target IBU.

if your going to use a recipe you need to adjust it to match your brewing process. if a recipe says to do a full boil of 5 gallons with 6 lb. of LME you don't want to put all that extract in 3 gallons then boil your hops. you wouldn't get nearly the IBU as you should get for the recipe. you would need to add 3.6 lb. of LME to get the same pre-boil gravity and the proper IBUs.

 

[JJ86]

Thanks. I'll definitely use the late extract addition to help with the hop utilization.

Regarding the Pre boil Gravity and OG, I have couple more questions.

1) Pre boil Gravity = Taken after steeping and prior to actual boil?

2) If my recipe does not include a Pre boil Gravity (Only OG), is there a formula I can use to determine what my PBG should be in order to reach that specific OG?

 

[Ohio-Ed]

Using extract, pre-boil gravity is next to useless. Pre-boil gravity is useful in AG to measure the amount of extraction you have gotten from the grain. In an extract, it is already done for you... It is what it is.

 

[TipsyDragon]

1. pre-boil gravity = taken after steeping and adding half your extract (or how ever much you need to hit your target SG)

2. if it doesn't specify a pre-boil gravity i always assume its a full boil recipe and act accordingly.

(target OG) * ((volume in gallons)/36) = lb. LME
(target OG) * ((volume in gallons)/44) = lb. DME

example: the recipe has an OG of 1.060 and you are doing a 5 gallon batch with a 3 gallon partial boil.

(60) * ((5)/36) = 8.33 lb. LME total for the entire recipe
(60) * ((3)/36) = 5 lb. LME for the boil

now this example doesn't account for steeping grain. that requires a little guess work. there are plenty of tools out there to estimate the OG from the steeped grain. all require you to estimate your efficiency. subtract the grains SG contribution from the SG needed for the recipe and enter that into the above formulas.

 

[TipsyDragon]

Using extract, pre-boil gravity is next to useless. Pre-boil gravity is useful in AG to measure the amount of extraction you have gotten from the grain. In an extract, it is already done for you... It is what it is.

thats not true. boil gravity affects hop utilization. if you don't have the proper boil gravity then your IBUs will be off. the amount of extract you add will change the wart's gravity and the IBUs. which may or may not be a good thing.

 

[JJ86]

So the DME and LME always stay constant at 44 and 36 pts respectively?

OK. Just to make sure I have this down. I was thinking about brewing the extract version of BierMuncher's Centennial Blonde (below). So if I am planning on doing a 3gal boil with DME, then I would use the below formual to come up with 3lbs of DME? Using this formula, I understand that the boil size reduces the amount of DME that is needed (Compared to the recipe). However, does this mean I will actually use 2 less lbs of DME extract or do I add the difference (2 lbs) after the boil?
(44) * ((3)/44) = 3lb. DME


BierMuncher Centennial Blonde
Batch Size: 5.50 gal
Boil Size: 6.57 gal
Estimated OG: 1.044 SG
Estimated Color: 3.2 SRM
Estimated IBU: 16.8 IBU
Brewhouse Efficiency: 70.0 %
Boil Time: 60 Minutes

Ingredients:
------------
Amount Item Type % or IBU
5.00 lb Extra Light Dry Extract (3.0 SRM) Dry Extract 83.3 %
1.00 lb Cara-Pils/Dextrine (2.0 SRM) Grain 16.7 %
0.25 oz Centennial [9.50%] (45 min) Hops 7.8 IBU
0.25 oz Centennial [9.50%] (20 min) Hops 5.1 IBU
0.25 oz Cascade [7.80%] (10 min) Hops 2.5 IBU
0.25 oz Cascade [7.80%] (5 min) Hops 1.4 IBU
1 Pkgs Nottingham (Danstar #-) Yeast-Ale

 

[Ohio-Ed]

thats not true. boil gravity affects hop utilization. if you don't have the proper boil gravity then your IBUs will be off. the amount of extract you add will change the wart's gravity and the IBUs. which may or may not be a good thing.

Sorry, guess I got distracted from the original point.
My point is that using extract, there is no efficiency calculation, so the preboil or OG should be able to be calculated. I think the impact of specialty grain would be little enough to not even worry about.

I agree that you need to consider the size of your boil on hop utilization.

 

[TipsyDragon]

So the DME and LME always stay constant at 44 and 36 pts respectively?

OK. Just to make sure I have this down. I was thinking about brewing the extract version of BierMuncher's Centennial Blonde (below). So if I am planning on doing a 3gal boil with DME, then I would use the below formual to come up with 3lbs of DME? Using this formula, I understand that the boil size reduces the amount of DME that is needed (Compared to the recipe). However, does this mean I will actually use 2 less lbs of DME extract or do I add the difference (2 lbs) after the boil?
(44) * ((3)/44) = 3lb. DME

well assuming your calculations are correct and they seem to be. then yes you would need 3 lb for the boil. but you also need to calculate how much you need for the total 5 gallons. which looks like another 2 lb. added at the very end of the boil to sanitize it.

and yes, LME almost always will have 36ppg (points per pound per gallon) and DME will almost always have 44ppg.

 

[goplayoutside]

I think your numbers are sound. It's wort gravity that affects hop utilization, so 3lbs DME in 3 gal water should give a similar gravity to 5lbs DME in the full boil and give you similar hop utilization. You may find yourself slightly under-utilized do to a proportionally larger wort gravity contribution from your steep and a proportionally larger volume reduction due to boil-off. I do partial boils using beersmith to calculate my extract additions based on my available boil volume and desired hop bitterness. I think the math there is basically the same. I would brew the batch that way and then adjust for future batches if necessary.

Another reason to avoid the over-concentrated boil is wort caramelization, which can leave you with some long-chain sugars that the yeast will have trouble chewing through. In a scotch ale or a porter or a doppelbock this might be a desirable thing, but it would not make a clean-tasting continental blonde. And it would darken the color. Late extract addition is a very good method and well proven. It also sets you up nicely for the partial mash transition using deathbrewers easy PM method, which I will attest works great.

Remember that a good fermentation can make good beer out of mediocre wort, but a bad fermentation will make lousy beer out of outstanding wort.

 

[JJ86]

well assuming your calculations are correct and they seem to be. then yes you would need 3 lb for the boil. but you also need to calculate how much you need for the total 5 gallons. which looks like another 2 lb. added at the very end of the boil to sanitize it.

and yes, LME almost always will have 36ppg (points per pound per gallon) and DME will almost always have 44ppg.

Thanks, helps alot. Will definitely use this for my next batch!

 

[JJ86]

Thanks, goplayoutside. Firing up a batch tomorrow, will definitely incorporate the late addition.