Best way to reduce gravity after the fact?

[Coastalbrew]

Recently my brew house efficiency has been going up on every batch. I started out in the high 60 to low 70% range, but my last 3 batches have been 81, 83, and 85%. My next brew is planned to have an OG of 1.073 @ my original 70% efficiency. If it comes in at even 80 percent it will be a much bigger beer than I want. My question is what is the best way to reduce the gravity post boil if it turns out to be bigger than I want? I figure I can just add water to dilute the wort, but what is the best way to calculate how much water to add? I buy my grains online, they are premilled and mixed, so just adjusting the grist is not an option. Would it be better to just adjust the batch size to account for the potential higher efficiency?

TIA

 

[day_trippr]

Consider approaching this from the optimistic side that the trend surely supports - but purchase some cheap insurance just in case: use an 80% brew house efficiency in your calculations - and pick up a bag of light DME. If your pre-boil volume * SG looks shy of the mark, use the DME to make up the difference.

Otherwise, you could use a dilution calculator like this one: Dilution And Boiloff Gravity Calculator - Brewer's Friend but you'll end up with greater volume (more of a potential catch when kegging).

Cheers!

 

[Coastalbrew]

Consider approaching this from the optimistic side that the trend surely supports - but purchase some cheap insurance just in case: use an 80% brew house efficiency in your calculations - and pick up a bag of light DME. If your pre-boil volume * SG looks shy of the mark, use the DME to make up the difference.

Otherwise, you could use a dilution calculator like this one: Dilution And Boiloff Gravity Calculator - Brewer's Friend but you'll end up with greater volume (more of a potential catch when kegging).

Cheers!

Thanks @day_trippr . I have unfortunately already purchased the grains using the old 70% efficiency in the recipe calculations, so now I guess my options are to either increase the batch size pre boil assuming the tend will hold, or wait until I have the post boil results and tweak based on the actual numbers. Thanks for the dilution calculator, that will definitely come in handy

 

[homebrewer_99]

I find adding .5 gal of water reduces the gravity by .005 points

 

[jdauria]

Use this..Dilution And Boiloff Gravity Calculator - Brewer's Friend Use #1, put in your current volume, current gravity and your target gravity and it will tell you what your new volume should be and how much water to add.

 

[Holden Caulfield]

I have unfortunately already purchased the grains using the old 70% efficiency in the recipe calculations, so now I guess my options are to either increase the batch size pre boil assuming the tend will hold, or wait until I have the post boil results and tweak based on the actual numbers. Thanks for the dilution calculator, that will definitely come in handy

Coastalbrew:

First do not adjust anything - no need.

There is a simple way to adjust your gravity before boiling whether your realized efficiency is greater or less than your plan and that is to know your target gravity kettle points and realized kettle gravity points before boiling, and then adding DME if you end up with fewer points or removing wort if you have too many.

The calculation for target kettle points (what you hope for) is (preboil gravity-1)*1000*preboil volume. In other words, if you preboil volume is suppose to 7 gallons and your preboil gravity is suppose to 1.040 then its just 40*7 or 280 point.

The calculation for realized kettle points is the same except use the realized value. For example, if your efficiency was higher than expected and you ended up with a preboil gravity of 1.043 and 7.2 gallons of wort, then your kettle has 43*7.2 = 310 points.

Since you extracted too many points (or sugars) you need to pour off 310-280 = 30 points of wort.

The gallons of wort you pour off is equal to the extra points divided by the realized gravity of your preboil wort or 30/43 or .7 gallons of wort.

After pouring off the wort just add back water to hit your target preboil volume.

If you have fewer points then expected, it is a similar process. Figure out how many points short you are, but instead of using the gravity of the realized wort, just use the gravity points for the DME, which is usually around 45. For example, if you extracted only 260 points and expected 280, you would need to add 20 points of DME in pounds which is equal to 20/45 or .44 pounds

Counting points and knowing how to adjust your preboil gravity is one of the most important skills to hitting your OG everytime. Increasing your volume to dilute or boiling more to concentrate are not good strategies as they also dilute or concentrate IBUs, altering your target recipe in a different way.

Here is a link to an excel recipe builder program I built that will do these calculations for you during brew day and the relationship to points.
https://www.dropbox.com/s/pc1vjpqre9dzjhz/Buildabeer v6.2 - DB.xlsm?dl=0
Good luck.

KB

 

[eric19312]

I'd suggest getting a refractometer and when you design your recipe calculate your target pre boil and post boil gravity and volumes. Preboil gravity and preboil volume determines your mash efficiency. If mash efficiency was higher or lower than targeted, use this information to calculate either a DME addition (if mash efficiency was low) or a how hard you boil (if high).

If mash efficiency was high into the kettle on a beer you would prefer not to come in high on OG then reduce boil to a simmer and/or reduce boil time. You may end up with more wort than your fermentor can handle at end of boil but could do a side 1 gallon batch or just take advantage of the larger volume to do a better job only pulling clear wort into the fermentor.

 

[Coastalbrew]

Thanks for all the advice, it was helpful.

Cheers!

 

[ncbrewer]

Another concern. With a possible range from 70 - 85% efficiency, you would probably notice the difference in perceived bitterness if you don't adjust hops to maintain the desired BU:GU ratio (unless you opt for one of the methods involving adjusting the sugar content).

 

[homebrewer_99]

Just to add a point, I find that when I boil outside in high humidity my boil off is greater than .5 gal every half hour.

That's what brought me to adding water to lower the post-boil gravity.

 

[emac813]

add water