Calculated SRM and Dilution

[skortjorkson]

Hello!

I've been practicing high-gravity brewing lately, brewing 10 gallons of wort and diluting it to 15 gallons in the fermentor. I'm planning on doing a baltic porter next, and want it to be quite dark.

I use Beersmith for my recipe calculations, and am already aware that hop utilization is not linear between a 10- and 15-gallon boil, i.e. that x amount of hops will provide more ibu/gal in a larger kettle than a smaller one. If I build a 15 gal. batch on Bsmith it will give me an inaccurate IBU calculation for my diluted batch, as it assumes a higher hop utilization. I need to build a 10 gal. batch and then use the following formula to determine the IBUs:

(10 x [10galIBU]) / 15 = diluted batch IBU

However, this time around I'm not making an IPA, but a dark beer, and I was curious if anyone knew whether SRM follows the same rules, as Bsmith definitely predicts a higher color utilization when I build a 15 gallon batch. Gravity, of course, remains constant, so I was curious: will the grain follow the gravity or the hops?

In the following article ( https://www.morebeer.com/articles/beercolor , in the "Assigning Color to Very Dark Beers" section) it states that dark beers do not follow Beer's Law of linear color dilution, stating that a dark beer diluted in half will not be half as dark as it was originally, but will actually remain darker.

So is Beersmith accounting for increased color utilization in a larger mash tun when I build a 15 gal. recipe? Or will it be accurate for a 10 gal. recipe which is then diluted, given Beer's Law does not apply? Or will neither be the case and I'll end up with a wimpy-looking porter? Anybody know?

 

[ajdelange]

When measuring a dark beer using the SRM (Standard Reference Method) one puts a few mL in a 1 cm cuvet, measures the absorption at 430 nm and multiplies that. by 12.7. Consider a beer that is 3*12.7 = 38.1 SRM. That means that A = 3 at 430 nm. Only the really expensive spectrophotometers and photometers have good performance at A of 3 and above and so the analyst must either dilute the beer or measure in a narrower cuvet. In diluting, one relies on Beer's law. In using a narrower cuvet one relies on a cuvet labeled 0.5 cm being exactly half the width of one labeled 1 cm.

In the ASBC MOA dilution is used. This says to me that in the opinion of the group that approves the MOA Beer's law is indeed valid. Whenever I measure a dark beer I use dilution but check for the validity of Beer's law. This is simple enough to do because even if you are in the shaky part of the instrument's range at 430 nm you will not be at longer wavelengths. If the absorption of the beer is 1 at some other wavelength and 0.5 at that same wavelength when the beer is diluted 1:1 then it is following Beer's law, at least at that wavelength and should, presumably therefore, be following it at 430 nm. To date I have not found a beer which violates Beer's law. Does that mean there isn't one? No. It just means they are, if they do exist, quite rare. Violation of Beer's law says that adding DI water somehow changes the chemistry of the chromatophors. I don't see how that would happen.

In any case I think your concerns about Beer's law are mooted by the miserable performance of the models that attempt to predict beer color from the grain bill. The fact that you have 60L caramel really doesn't tell you much about the color that malt will produce unless one does a Congress mash with it and measures the color with a Lovibond Tintometer. That same malt, subject to a more normal mashing procedure may produce a substantially different color (for example a wort boiled 2 hrs will be a lot darker than one boiled half an hour) even as measured by a Tintometer and the relationship between SRM and °L is very shaky.

Given the limitations of the color prediction programs I think you are on solid ground assuming that if you have a beer with a given SRM adding water will dilute the SRM linearly. IOW once the chromatophors are in the beer beer's law holds. Keeping the same mash water and adding more grain may be different. In the thicker mash extraction of chromatophors may be more or less than it is in a thinner mash. Also we again note that extended boiling results in additional color development.