Stout hasn't reached final gravity

Larse said:

What I'd like to know is how much? What's the target pH and how many points does it need from say as @peebee mentioned; 4.9?

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You’re looking to achieve a mash pH of around 5.4 because this is the sweet spot for the enzymes to do their magic and produce a good quality fermentable wort. Mash pH is not the same as your water pH which has little impact on the mash pH.

If you use distilled water (no alkalinity) you are likely to get a mash pH around 5.6-5.8 for light coloured grains and maybe below 5.0 for some of the darker grains. Adding calcium salts will lower this mash pH even further through its interaction with phosphates in the malt but you do need calcium, somewhere between 50 and 150ppm is common.

So without alkalinity the mash pH might be okay for very pale ales but the mash pH of dark ales is likely to be well below where you want it. Alkalinity moves the pH up and resists the acidification of the mash and needs to be higher in darker brews (assuming the dark grain is added to the mash).

There are rough values for alkalinity that work in practice and that most people use if they’re not relying on brewing recipe apps to do all the working out for them. For black beers you might want 150ppm alkalinity, for very pale beers maybe 0-20ppm and in between pick a number that feels about right for the colour.

Armed with this you then need to know what the alkalinity of your water is and how it can be changed. Reducing alkalinity can be done in many ways including dilution with distilled/RO water, addition of other salts (including more calcium), or addition of acid. Increasing alkalinity can be done by adding high alkalinity water from some other source, or adding carbonate salts (eg sodium bicarbonate or calcium carbonate). For example 0.1g of sodium bicarbonate per litre of water adds 60ppm of alkalinity.

Right, I’ve finished my pain au chocolat so that’s all you’re getting for now

peebee said:

Coo ... if it was so easy!

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This is talking about the distribution of hydrogen ions and the measurement of "pH". It's so heavy I can't lift me head off the table just thinking about it. There's no direct relationship with "CaCO3" and pH, but there are ways of roughly predicting pH. That's what the DIpH stuff is about … the pH of a mix of a said malt in distilled water. "Malt"? ... Is it dawning on you yet? The complexity of this caper? And the results are probably no better than weather forecasts (they're right some of the time!).

And you'll hear people saying they've got the pH bang on expectation. Eh? I've just been going through all this, and still have the energy to talk about it. Should wear off soon?

(Where's that damp towel … I need to wrap me head in it).

Thanks @Hazelwood Brewery! Me head's so heavy now the table's broke.

Hazelwood Brewery said:

The challenge though is how much is dissolved over what time and are any other variable like temperature highly relevant. As peebee said, how do you know when it’s done and what you’ve got.

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If measure how much you add, and none is left precipicated on the bottom of the vessel you use, then you know its all dissolved. You could also measure the resultant alkalinity, or monitor with a TDS meter.

Sadfield said:

If measure how much you add, and none is left precipicated on the bottom of the vessel you use, then you know it’s all dissolved. You could also measure the resultant alkalinity, or monitor with a TDS meter.

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I’m not sure about the precipitation (maybe?). TDS could be a plan, I’ll build that into my trials and see what we can learn from it.

Hazelwood Brewery said:

You’re looking to achieve a mash pH of around 5.4 because this is the sweet spot for the enzymes to do their magic and produce a good quality fermentable wort.

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Does low pH influence fermentability? Mesh and kettle sours and the final pH of all beers would suggest not.

Sadfield said:

Does low pH influence fermentability? Kettle sours and the final pH of all beers would suggest not.

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Lower pH in the mash (5.0) favours beta-amylase so the wort should be more fermentable because of the greater proportion of simple sugars. If you’re souring in the kettle, the mash is already done and the pH is now about fermentation rather than fermentability.

This is science though so how much of a difference it makes in the real world and how you could tell it was the pH and not some other factor

Hazelwood Brewery said:

TDS could be a plan

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You think? An electronic TDS meter is a great tool for noting a variation. The "TDS" is actually the electrical conductivity multiplied by a "factor". The "factor" is accepted to be 0.65. In reality it could be between 0.5 and 1.5 (or something like that). After pH prediction I think you've just skipped from the frying-pan into the fire?

As for measuring "Alkalinity": I was very hopeful of this. I bought a Hanna "Alkalinity tester". Great bit of kit, uses a colourimeter device to really figure out colour changes (better than your eye). Cost a bit (£80) but for the sake of Science …

But they were hopeless at the extreme low end giving me 12.5ppm as CaCO3 when it was measured by old-fashioned titration as 7 or 8. I'm hoping by lifting the alkalinity off rock bottom (adding measured doses of bicarbonate) it'll start being more reliable? But the indicator is about out-of-date, and it costs about £35 and lasts 8-12months (ish).

Hazelwood Brewery said:

Lower pH in the mash (5.0) favours beta-amylase so the wort should be more fermentable because of the greater proportion of simple sugars.

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So the OP did produce a good fermentable wort.

peebee said:

You think? An electronic TDS meter is a great tool for noting a variation. The "TDS" is actually the electrical conductivity multiplied by a "factor". The "factor" is accepted to be 0.65. In reality it could be between 0.5 and 1.5 (or something like that). After pH prediction I think you've just skipped from the frying-pan into the fire?

As for measuring "Alkalinity": I was very hopeful of this. I bought a Hanna "Alkalinity tester". Great bit of kit, uses a colourimeter device to really figure out colour changes (better than your eye). Cost a bit (£80) but for the sake of Science …

But they were hopeless at the extreme low end giving me 12.5ppm as CaCO3 when it was measured by old-fashioned titration as 7 or 8. I'm hoping by lifting the alkalinity off rock bottom (adding measured doses of bicarbonate) it'll start being more reliable? But the indicator is about out-of-date, and it costs about £35 and lasts 8-12months (ish).

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Yes, I’m aware it measures conductivity and I don’t know how helpful it might be but if we throw enough tools into the mix something might be helpful. TDS for example might be used to indicate “when it’s done” even if it can’t say how much alkalinity you’ve got. Think of it like a hydrometer indicating that fermentation is done when you get several readings the same…maybe?

Sadfield said:

So the OP did produce a good fermentable wort.

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Absolutely. The tread has taken on a life of its own. I might get Chippy to rename it “Everything you wanted to know about brewing in 150 easy to read pages”.

We’re not there yet but we’ve made a good start

OK, I have some preliminary feedback on making high alkalinity water…

To start, I cleaned 3 fizzy drinks bottles (2 litre) with sodium percarbonate, rinsed each in fresh water, then rinsed each in Starsan, finally rinsing three times with distilled water. I hoped that this would mean there was no trace of anything alkaline or acidic in each bottle. I used three bottles because I wanted to see the effect of this trial with different starting points in terms of alkalinity.

In the first bottle I added 1 litre of distilled water (A).


In the second (B) I added 900ml of distilled water + 100ml of my tap water.


In the third (C) I added 750ml of distilled and 250ml of my tap water.


This gave me a starting point of 0, 16, and 39 ppm alkalinity respectively. TDS showed 2, 39, and 87. Calcium was 0, 10, and 25.

Then I added to each bottle 10g of precipitated chalk, this stuff…



After adding the chalk I gave the bottle a good shake and you can see it turned very milky.


I then squeezed all the air out of the bottles, which I fitted with a carbonation cap, and pressurised each bottle to 25psi with CO2.


I left the bottles on my worktop and every couple of hours through the day, gave each bottle a good shake.

The next day - actually it was later in the day so probably after a day and a half, I wanted to see if there had been much change in alkalinity. The bottles at that point looked like this…


This is where I had a problem, as soon as I loosened the cap the torrent of bubbles escaping from the water stirred up all that sediment and I was left with a murky test sample. No point measuring this!


So at this point I gave each bottle a good shake or six to release all the CO2 and I left the bottles on the worktop having given them a slight squeeze to encourage any remaining CO2 to leave solution. I left them to settle for another day.

This morning the bottles were fairly clear so I thought this might be okay to test.


In the end I only tested the first bottle because this simple trial has shown very encouraging results. In fact it’s worked too well and maxed out my test kits because the alkalinity is off the scale. I couldn’t accurately measure it but I think the alkalinity is well over 1000ppm.

I need a rethink before my next attempt but I might just leave the bottles for now and next time I collect some RO water I’ll dilute some of these test samples by say 10 to 1 and measure those.

So pretty fair to say that the amount of chalk needed to achieve the alkalinity desired for a stout 50-100ppm, will dissolve if you treat your water in advance.

Sadfield said:

So pretty fair to say that the amount of chalk needed to achieve the alkalinity desired for a stout 50-100ppm, will dissolve if you treat your water in advance.

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Does that treatment also require CO2? I notice there seems to be a fair bit of sediment at the bottom of those bottles.

Sadfield said:

So pretty fair to say that the amount of chalk needed to achieve the alkalinity desired for a stout 50-100ppm, will dissolve if you treat your water in advance.

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Very probably, if you treat a day in advance.

Larse said:

Does that treatment also require CO2? I notice there seems to be a fair bit of sediment at the bottom of those bottles.

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Yes but the air has lots of CO2. Pressurising the bottles with pure CO2 speeds the process markedly.

The sediment is precipitated chalk not yet dissolved into the water - I did rather overdo it though because I wasn’t sure how much might be needed, in the end it looks like far less is needed than I used!