Double Batch Size Efficiency Adjustment

[BrewerDon]

I'm an experienced homebrewer - experienced on my equipment. I brew 5 gallon batches. I double batch sparge.

I was given a keggle and so now I'd like to brew a 10 gallon batch. Before I do that I want to get my ducks in a row. I've seen posts on this forum that say to just double everything in your recipe and you are good to go. That can't be right because the boil off rate is constant.

To make the math easier let's say that I normally start with 7.5 gallons of wort and boil for 1.5 hours down to about 6 gallons. This is a boil off rate of 1 gallon per hour.

If I double the amount of grain that I normally use in a given recipe and also double the amount of hot liquor, my boil off ratio will still be 1 gallon per hour so after 1.5 hours of boiling my wort, my wort will be more dilluted and will have a lower S.G. I would be starting with 15 gallons of wort and ending up with 13.5.

So instead of doubling the starting amount of wort, I need to start with 13.5 gallons of wort. After 1.5 hours of boiling that will put me at 12 gallons of wort (2 x 6 gallons) - a double batch. However, because I used less hot liquor to sparge with I will surely have a lower starting gravity then I do when I brew a single batch. Therefore, I will need to more than double my grain bill right?

So if everyone agrees with what I have said so far then my question is:

How much of an adjustment to my grain bill do I need to make to compensate for the fact that my hot liquor to grain ratio has changed?

 

[ancientmariner52]

I'm not sure your boil off rate will be unchanged. Surface to volume ratio has changed, volume has changed, firing rate will have to change.

With that in mind, I doubt if the rate will decrease. So, if you simply double the batch, you will have the same or likely higher gravity. Add boiled water to correct the gravity, and note your new boil off rate for next time.

I'm basing this on the fact that a bigger boiler makes more steam. Hope this helps. Good luck!

 

[BrewerDon]

I'm not sure your boil off rate will be unchanged. Surface to volume ratio has changed, volume has changed, firing rate will have to change.

With that in mind, I doubt if the rate will decrease. So, if you simply double the batch, you will have the same or likely higher gravity. Add boiled water to correct the gravity, and note your new boil off rate for next time.

I'm basing this on the fact that a bigger boiler makes more steam. Hope this helps. Good luck!

I don't think you are following me. The boil off rate may change but it certainly will not double. Therefore, if I merely double the amount of water and double the amount of grain and boil for the same length of time that I normal boil for I will have a *lower* S.G. not higher.

 

[ancientmariner52]

I don't think you are following me. The boil off rate may change but it certainly will not double. Therefore, if I merely double the amount of water and double the amount of grain and boil for the same length of time that I normal boil for I will have a *lower* S.G. not higher.

Yes, I see what you mean. Perhaps a test boil with just water? I think it is very likely that the rate will change, but all the formulas I have available are based on locomotive and marine boilers, so not really applicable.

 

[wilserbrewer]

I've seen posts on this forum that say to just double everything in your recipe and you are good to go. That can't be right because the boil off rate is constant.

?

Boil off is not constant between a ten gallon and 5 gallon brewery.

Doubling a recipe to go from 5 to 10 gallons is a sound approach unless you have data indicating otherwise.

You may want to reduce total water a bit given your boil off likely will not be double, or carefully monitor boil off and adjust boil vigor as you proceed.

You can also extend the boil and hold back your late hop additions and time them to flame out as increasing boil time on initial bitter hops will not have a great overall effect.

Let experience dictate, or you could run a test boil but that seems like a waste of energy imo.

 

[JONNYROTTEN]

This is one of those relearning your new system things.
Get a few batches under your belt to learn your setup and go from there. I double all recipes for 10 gallon batches and start with around 15 gallons for 12 to 13 gallon post boil. Your not going to be able to do full boils in a 15 gallon keggle.

 

[BrewerDon]

Thanks for all of the comments on boil rate. The pot that I currently use is almost the same diameter as the new keggle. The keggle is just taller so since the surface area of the wort will be about the same I am predicting the same boil off rate. I may be proven wrong on that but for now please humor me. By me giving so much extra information on why I am asking my original question, the question itself has been lost.

Let's totally remove boiling from the equation.

What I really am trying to get is some input on is how to adjust my grain bill when the total water to grain ratio changes. For example, I currently have a recipe that uses 8 pounds of grain and 9 gallons of water. After a double batch sparge, I end up with 7.5 gallons of preboil wort with a gravity of 1.037.

How do I scale the grain bill so that I end up with 13.5 gallons of wort with a gravity of 1.037? I'm certain that the grain bill will need to be more than 16 pounds but how much more?

I know that I will have to experiment and dial this in but I'm looking for input to help me make a good educated guess. This is a difficult question I think.

Another way to look at this is:
If on a brewers system, 8 pounds of grain and 9 gallons of water yields 7.5 gallons of 1.037 wort then 8 pounds of grain and 8.25 gallons of water will produce 6.75 gallons of wort at a gravity of _______?

 

[GJOCONNELL]

BeerSmith 2.0....MIC DROP!

 

[wilserbrewer]

You are trying to adjust the grain bill to have the same pre boil gravity for the single and double batch.

This will not produce the same post boil gravity if your boil off is the same. Logic flawed imo.

 

[BrewerDon]

You are trying to adjust the grain bill to have the same pre boil gravity for the single and double batch.

This will not produce the same post boil gravity if your boil off is the same. Logic flawed imo.

Your are right, my logic is flawed. I was trying to ask my question in such a way where people would stop focusing on boil off rate.

The bottom line is that I am going to change my water to grain ratio. With less water to grain my efficiency will go down. It's a matter of making a new equipment profile in BeerSmith for 10 gallon batches. But BeerSmith needs me to enter the thing that I have been hoping to get with this post - BH Efficiency. It's going to be less than it was for my 5 gallon batches. Obviously I will have to brew and adjust. Since I will now be brewing 10 gallons I wanted to get close the first time and I was just hoping that someone had done something similar and had a good suggestion on how much of a hit my BH Efficiency is going to take. Since no one seems to have any idea I'm going to predict that I will take a 7% hit, I will enter that in BeerSmith and it will increase my doubled grain bill by this amount.

 

[wilserbrewer]

7% seems high in my world of guessing...ymmv

 

[BrewerDon]

7% seems high in my world of guessing...ymmv

I appreciate the input. Based on that I will go with 5% in stead of 7%. Thanks.