8 Gal Pre-Boil=Low OG?

[dustinboyd]

I've researched a lot of threads and have not been able to find a clear answer to my question.

First off I found after researching that it seems like no one needs to start with 8 gallons pre-boil to end up with 5 gallons in the keg. For some reason I do though. I get 6 gallons into the primary, about 5.25 into the secondary, and then usually an even 5 into the keg. There is usually a lot of trub left in the primary.

Also I consistently am one point low on my OG. I guess first I should clarify....I don't know exactly what one point is. If the OG should be 1.07, I will end up at 1.06. (Is that 1 point or is that 10 points?).

Is my low OG because of my 8 gallon preboil volume? Also, what can I do to fix this? I know DME and Honey and other stuff can be added at the end, but I guess what can I do to fix the root of the problem, needing 8 gallons of preboil volume? I've read that boiling with the lid on is not good, but that's the only idea I had.

Thanks for the help.

 

[Psylocide]

Are you adjusting the grain bill?

Your pre-boil OG should be low too if you're using a grain bill meant for 7-7.5 gal pre-boil volume.

Seems like an awful lot of boil off though... how are you measuring your volumes?

 

[TechyDork]

What is the efficiency of the recipe(s) you are using? Most are setup for 70-75%. Sounds like maybe your not getting as high of an efficiency as the recipes are designed for. If your efficiency is lower than what the recipe was designed for that would lead to you getting a lower OG?

As for your pre-boil volume, if you start with 8 and then boil off 1 or 1.25 gallons and then leave .5-.75 behind in the kettle with the trub that would sound about right to me.

Are you using any software or recipe calculators to get what your OG and volumes should be?

 

[dustinboyd]

No I have not adjusted the grain bill, I don't know why I didn't think of that, that's probably my problem.

I'm not sure what you mean by asking how I measure... Grain is by weight and water is by volume, I have a one gallon pitcher I use to measure, like the kind a restaurant kitchen uses.

The recipes I make are normally 70-75% efficiency target like you mentioned...I don't know what my actual efficiency is, I've never checked it. I don't use software or brewing calculators, I just follow the recipe as written. Normally it's a recipe I found on here or brewers friend.

 

[Psylocide]

No I have not adjusted the grain bill, I don't know why I didn't think of that, that's probably my problem.

I'm not sure what you mean by asking how I measure... Grain is by weight and water is by volume, I have a one gallon pitcher I use to measure, like the kind a restaurant kitchen uses.

The recipes I make are normally 70-75% efficiency target like you mentioned...I don't know what my actual efficiency is, I've never checked it. I don't use software or brewing calculators, I just follow the recipe as written. Normally it's a recipe I found on here or brewers friend.

I guess I meant how do you know what the post boil volume in your kettle is?

Are you taking a pre-boil gravity reading after your wort is collected?

 

[iijakii]

Well there's your problem. You're adding more water to get more volume, but not scaling up your grain. Just diluting it to get a smaller OG.

 

[FourSeasonAngler]

Also the difference between 1.07 and 1.06 is 10 points not 1. That is why gravity reading are always expressed to the thousandths. (ie: 1.065, 1.072 ect...)

 

[dustinboyd]

I just know my post boil volume by what ends up in the fermenter, plus I estimate.25 gal left in the kettle.

I do not take a pre boil gravity reading, mostly because I never have needed it since I don't check my efficiency, I am going to start though.

I think my question was answerd, thank you everyone for the fast responses!

 

[dustinboyd]

Actually I have one more question. How do I know how much grain to add? I think I have the answer but I want to double check...

Let's say I have a recipe that is intended for a 7 gal pre boil. I divide each grain ingredient by 7, giving me the amount of grain per 1 gallon of pre boil volume. Then multiply that number by 8(my pre boil volume), and thats my final grain bill. Is this right?

 

[FourSeasonAngler]

Use a recipe calculator that has an option to "scale" up or down. Brewtoad is free and does this, I think the recipe calculator on Brewer's Friend does as well.

 

[Gavin C]

The grain bill and percentage will target the volume to the FV. The preboil volume doesn't matter at all if your hitting that target.

Most recipes will be 5 gallons, 5.25 gallons or 5.5 gallons into the FV.

The important figure you mention is 6 gallons to the FV. That is the key. The grain bill needs adjustment to allow for a 6 gallon target at desired OG.

Forget the preboil volume. Not a concern if you are hitting the target volume to the FV unless you are not accounting for large trub loss in the kettle.

and yes it's a 10 point difference you describe which is significant but then so is 10-20% error in volume (6 gallon volume for a 5 to 5.5 gallon grain bill)

 

[dustinboyd]

That explains it very well, thank you.

 

[Gavin C]

No worries. Happy to help.

For what it's worth. I think you are losing too much in your fermentation vessel(s).

I target 5.5 gallons in the primary FV in my equipment setup and rack to the keg leaving 0.5 gallons to allow for a hydrometer sample or two and trub. Almost never, do I not get a full 5 gallon keg. (Never use a secondary so don't concern myself with losses there, but that's a different thread)

YMMV but on my setup for a typical 5.5 gallon batch with an approximate OG of 1.055 I use approx. 11lbs of grain and my volumes would be roughly

7.5 gallons strike water (with BIAB)
-0.5 gallons lost to grain absorbtion

7 gallons pre-boil (no different from here on with any all grain process)
-1.25 gallon boil off in 60 mins
-0.25 gallon lost to kettle trub, chiller and hoses

5.5 gallons to FV at target OG
-0.5 gallons loss to measurement and FV trub

5 gallons of tasty beverage into keg

 

[dustinboyd]

I see what you're saying and I think you're right. Before I try to adjust the grain bill, I'm going to try to get my process down better for less loss.