Calculating ppm for acid additions

[RichHall]

Hey folks

Just wondered how I should go about calculating ppm for acid additions?

I've been using CRS/AMS to reduce alkalinity, but Brewfather doesn't include this - and I'm preferring recipe results from Brewfather over Brewers Friend lately.

So, I'm thinking of switching to lactic acid to reduce alkalinity, but understand the flavour threshold is around 400ppm.

My guess at calculating ppm was to work on ml/l and multiply by 1000, but then I stumbled across something online which talks about adjusting for the density of the lactic acid - at which point I got confused and thought it might be easier to ask!!

A recipe I'm putting together at the moment, calls for 4.3ml of lactic acid (80% strength) to hit the mash PH and my total water volume is 22l. My guess at calculating ppm was therefore:

4.3ml x 80% = 3.44ml total acid content
3.44ml/22l = 0.156 ml/l acid addition
0.156ml * 1000 = 156 ppm

Am I on the right tracks, or have I guessed completely wrong?!

Cheers

 

[strange-steve]

I think your only mistake is that you've used ppm as a volume fraction rather than a mass fraction, which I believe is what was used for the suggested taste threshold of 400ppm. In other words I believe it's mg per litre rather than ml per litre, which in this case doesn't make a huge difference, but there is a difference.

To convert you need the density of lactic acid, which is 1.2 g/ml, and so 1ml of the 80% lactic acid contains 960 mg of lactic acid. That means the 400 ppm taste threshold is equal to 0.42 ml/l of 80% lactic acid.

As for your example above, 4.3 ml in 22 litres is 0.2 ml/l and so well below the suggested threshold.

 

[RichHall]

Thanks Steve, that's really useful.

I've ran that through some old recipes, and it seems I get above the suggestion of 0.3ml/l in your beginners guide, but still within the suggested 400ppm limit - so lactic might not cover all recipes for me - which then makes me wonder about using phosphoric instead?!

Which I understand is flavour neutral, and given it's strength, needs very little overall addition by comparison to CRS/AMS.

Any reason to avoid using phosphoric? (Other than the need for careful handling)

Cheers

 

[strange-steve]

I get above the suggestion of 0.3ml/l in your beginners guide, but still within the suggested 400ppm limit

Don't worry too much about that 0.3ml/l max, that was put in as a conservative maximum because some people reportedly can taste lactate at considerably less 400ppm.

Any reason to avoid using phosphoric?

If you want to use it then go ahead, I don't have any personal experience with it but one potential issue is that it can cause precipitation of calcium during the mash. Whether or not that's an issue however is very much open to debate.