Calculating IBU when adding DME late...

[RustyHorn]

My beers have been turning out a little darker than they should so I have decided to add the DME at the end as it doesn't need to boil. What I am wondering is: If I boil the hops in water (I can calculate the IBU when just extracted with water) then add the DME at the end, will adding the DME lower the IBU already calculated?

Hope this makes sense!

 

[oljimmy]

As I understand it, hops need at least a low-gravity wort to achieve acid-utilization properly... you can add some of the DME at the start and more at the end, but water-based "hop tea" is not the same thing as properly extracted hop acids in wort. Something about the hops needing some of the compounds found in wort to do their thang. Just something I heard Jamil say on BrewStrong once.

 

[RustyHorn]

I added half my DME. What I want to know is if I add DME at the end, does it lower the previously calculated IBU?

 

[Qhrumphf]

Adding half your DME at the start, and half your DME at the end will actually slightly RAISE the calculated IBUs. From that I understand, the impact of wort gravity utilization on is smaller than a lot of folks (and calculators) make it out to be, but less sugars in the wort should allow a little more isomerization.

 

[The_Bishop]

This can help you figure that out:
http://www.howtobrew.com/section1/chapter5-5.html

 

[RustyHorn]

Adding half your DME at the start, and half your DME at the end will actually slightly RAISE the calculated IBUs. From that I understand, the impact of wort gravity utilization on is smaller than a lot of folks (and calculators) make it out to be, but less sugars in the wort should allow a little more isomerization.

Thank you for your reply. Could you elaborate on this further? When I use an IBU calculator is says differently. However, the calculator only takes into consideration boiling for the whole 30 minutes, not adding the DME at flameout.

 

[RustyHorn]

This can help you figure that out:
http://www.howtobrew.com/section1/chapter5-5.html

Thank you, but this still doesn't answer my question.

 

[Qhrumphf]

What calculator are you using? Some are better than others. If you use something like BeerSmith, you have the option to put sugars and extracts in as late additions, or post-boil/fermenter additions, and in doing so, the IBUs raise slightly. Not all calculators are equipped to do that. In which case, I would simply omit the late extract from the recipe, only adding the stuff you add at the beginning, to get an approximation of where your IBUs are.

 

[TrickyDick]

I find the whole IBU thing funny.

There are calculators and you can choose on some which model to use : Rager, Tinseth, etc. Each model presumably gives the correct value?

There are also hop age calculators that estimate how much alpha acids disintegrate over time. Also I do not really know how they test each crop from one year to the next and from plant to plant, cone to cone how much variability is there and how uniform is the particular harvest. I assume this must be fairly consistent, but makes me wonder what the swing or standard deviation is.

Then there is the uncertain storage conditions of the hops so you really can't be certain what you are getting in those pouches, especially if you mail ordered them.

Next the measuring of the hops. How accurate is the scale? How accurate is the packaging?

Next is the boiling. How intense is your boil? I have noticed that when I switched from a low pressure regulator to an adjustable pressure regulator on my propane boil kettle, that I was able to dial in a more robust boil intensity and the bitterness was much better (more in line with what the recipe predicted)

The calculators are only going to get you so close to your target I have decided because of all these variables. If you brew one recipe repeatedly, you will begin to learn and dial-in the bitterness, being careful to record the particulars of each brew session to see what the variables were and get closer and closer to your target. Color I think works pretty much the same way as far as dialing-in.

BeerSmith does a good job of predicting most of the variables for me, and I believe as was mentioned, can also do the late addition calculations.

TD

 

[Qhrumphf]

I find the whole IBU thing funny.

There are calculators and you can choose on some which model to use : Rager, Tinseth, etc. Each model presumably gives the correct value?

There are also hop age calculators that estimate how much alpha acids disintegrate over time. Also I do not really know how they test each crop from one year to the next and from plant to plant, cone to cone how much variability is there and how uniform is the particular harvest. I assume this must be fairly consistent, but makes me wonder what the swing or standard deviation is.

Then there is the uncertain storage conditions of the hops so you really can't be certain what you are getting in those pouches, especially if you mail ordered them.

Next the measuring of the hops. How accurate is the scale? How accurate is the packaging?

Next is the boiling. How intense is your boil? I have noticed that when I switched from a low pressure regulator to an adjustable pressure regulator on my propane boil kettle, that I was able to dial in a more robust boil intensity and the bitterness was much better (more in line with what the recipe predicted)

The calculators are only going to get you so close to your target I have decided because of all these variables. If you brew one recipe repeatedly, you will begin to learn and dial-in the bitterness, being careful to record the particulars of each brew session to see what the variables were and get closer and closer to your target. Color I think works pretty much the same way as far as dialing-in.

BeerSmith does a good job of predicting most of the variables for me, and I believe as was mentioned, can also do the late addition calculations.

TD

All very true. It's an estimate and nothing more. Consistent process and consistent formulation is more important. Using Tinseth for one and Rager for another won't help you.

I'm just trying to say, depending on your source of information, late extract additions either have no impact on IBUs, or a slight increase. The IBUs will not decrease as the OP originally thought.

 

[RustyHorn]

I'm just trying to say, depending on your source of information, late extract additions either have no impact on IBUs, or a slight increase. The IBUs will not decrease as the OP originally thought.

Brilliant. That answers my question perfectly. Thank you for your help! I wonder how helpful you'd have been had I told you earlier that I'm a Gooner?

 

[Qhrumphf]

Brilliant. That answers my question perfectly. Thank you for your help! I wonder how helpful you'd have been had I told you earlier that I'm moving back to Woolwich?

I'd say carry on as planned.

 

[RustyHorn]

I'd say carry on as planned.

Unfortunately I don't remember the Woolwich days. Mainly because I hadn't been born. Neither had my dad. Or my granddad. Or my granddad's dad ;-)

 

[budbo]

The hops will give up acids based on boil time, adding the DME last 10-15 minutes will just sweeten your "Hop Tea" and make it Wort. It will be lighter but if you truly want a light straw colored beer all grain is the way.