Converting "malt acidity as ml of 0.1N NaOH per 100 ml of wort" to buffering capacity

[qmax]

This acidity number is commonly found in malt specification sheets in my part of the world. I was geeking out all night and came up with a way to convert this number to malt buffering capacity.

You will need the following numbers that can be found in malt technical specifications:
Malt DI pH; Acidity as ml of 0.1N NaOH in 100ml wort; (Malt moisture content; dry basis extract. <<< optional)

First, I'll break it down into the steps I took to arrive at buffering capacity:

From dry basis extract and malt moisture content, you figure out "extract as-is" which allows you to figure out the laboratory/Congress mash gravity.

I found two descriptions of a Congress mash used in different parts of the world:
A Congress Mash is FGAI malt mashed at 50g per 400g of water (at 20`C)
A Congress Mash is FGAI malt mashed at 1 lbs per 1 gallon of water (at 20`C)

Then you can figure out exactly what amount of malt and water need to be in 100 ml of wort of this gravity.

After that, you divide the mEq contribution from NaOH by the mass of the malt and the pH difference from the malt DI pH to the end titration pH which is 8.3-8.5 (for phenolphthalein).

This is easier said than done, but after a couple of days I finished a spreadsheet with this conversion.
I'll upload it to a random file sharing service for anyone who needs it, as homebrewtalk doesn't allow *xlsx attachments.
Here is the link: http://s000.tinyupload.com/?file_id=59794433111821755475

 

[ajdelange]

This acidity number is commonly found in malt specification sheets in my part of the world.

This is exactly (almost exactly) what we need. Which part of the world is this?

You will need the following numbers that can be found in malt technical specifications:
Malt DI pH; Acidity as ml of 0.1N NaOH in 100ml wort; Malt moisture content; dry basis extract.

This must assume a standard mashing procedure such as the Congress mash such that you know how much malt went into 100 mL wort.

But it appears you've figured that out..

Then you can figure out exactly what amount of malt and water need to be in 100 ml wort of this gravity at 100% efficiency.

After that, you divide the mEq contribution from NaOH...

0.1 mEq/mL

...by the mass of the malt and the pH difference from the malt DI pH to the end titration pH which is 8.3-8.5 (for phenolphthalein).[/QUOTE]

Yes, more or less. Were the buffering of malt constant with pH then this would be fine but it isn't. There is non linearity which depends on the particular malt and, of course, the pH. Measuring the P alkalinity of a malt will give you the average between DI mash pH and 8.3. For example a particular caramel malt (60L) I measured has a DI mash pH of 4.76 where its buffering is right around 100 mEq/kg-PH. At pH 5.2 the buffering is 62, at 5.4 58 and at 5.6, 5.6. At pH 6.6 it is back up to 80. In using these data we are concerned with the number of protons it takes (or are yielded up) in going from the DI pH to the mash pH - not to the P acidity point. Rats!

But what they are doing is better than nothing. All I need to do is convince the maltsters to give us data in the form of a simple Taylor series expansion about the DI mash point.

mEq = c1*(pH - pHdi) + c2*(pH-pHdi)^2 + c3*(pH - pHdi)^3

For example, then, the malt I mentioned above would be characterized by
pHdi =4.76, c1 = -89.68, c2 = 31.84, c3 = -10.1

AFAI can see you are doing things right but the data isn't great.

Looks like the potential for interesting discussion here but I will be away for a few days.

 

[qmax]

My part of the world is Russia. However, I'm pretty sure we aren't the only ones who commonly use this number.

The Taylor series or any regression is a great idea. I'm all for it

Although if every batch of every malt got consistently labeled by the maltster with an updated value of buffering capacity for any reasonable pH, it would be a huge step forward. Right now, AFAIK, it's a common practice to put a malt in either base, crystal, or roasted category and assign it some sort of average number across the group, or try to derive it from the malt color rating.

 

[ajdelange]

The purpose of the congress mash is to determine how much extract can be obtained from a given weight of malt. I don't have the details available now but in essence 100 (I think) grams of malt are ground to prescribed fineness using a particular mill and mashed with carefully measured amount of distilled water through prescribed temperature steps. The wort is separated and filtered. The resulting solution contains a known amount of water and all the extract from the 100 grams of malt. Specific. Gravity is measured and converted to Plato which is the percent extract by weight of the wort. Multiplying by volume of wort, its specific gravity and the density of water gives the grams of extract from 100 grams of the malt which is the efficiency of conversion. To determine the amount of this grain needed for a particular amount of extract convert the efficiency to a fraction and divide by the fraction. For example if the congress mash yielded 80 grams extract per 100 grams the efficiency is 80% (0.8). To get 1 kg of extract you would need 1/.8= 1.25 kg of malt if your mashing process is as good as the congress mash. If it isn't then you need to multiply the congress efficiency factor by another factor representative of relative losses in your brewery. Commercial brewers get close to congress mash numbers. Home brewers about 10% lower.