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Old 11-30-2012, 02:04 PM   #1
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Default pH for dummies?

I just got my pH meter back. It worked, briefly, but it drifted pretty quickly. Aside from not recommending the Milwaukee pH meters, I will just suck it up.

Anyway, I checked the pH of my mash while it seemed to be "close enough" going back and forth between the buffers.

The mash pH was 5.29. That seemed low (Brunwater predicted 5.5) but then I remembered that I finished off the bag of Rahr two-row and if I remember correctly that base malt has a much lower pH in distilled water. (5.5 I think).

That was fine, and then for the first time I took the pH of the finished wort after the boil. It was 5.35 at 59 degrees.

That got me thinking about things I've read and heard about the pH during the entire brewing process.

I know there are big thick textbooks about this, but if anyone has the time and inclination to give me the cliff notes, I'd appreciate it.

The reason I ask is that this is the very first time my wort was not completely clear in the fermenter. The hydrometer sample did start to drop clear after sitting a bit, but usually it's clear right out of the CFC.

I know that many things go into this- calcium content, the pH, break material, etc, but in this case I'm thinking it has to be the pH.

Why does the pH change from the mash through the boil? What's the optimum pH for the wort, and why? I understand why the pH would change during fermentation, of course.

Am I on the right track here, or way out to lunch? (I figure a 50/50 chance at either!).

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Old 11-30-2012, 04:15 PM   #2
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i'm writing an email to a local brewer on this topic and saw your post by coincidence, if he has anything useful to say on the matter i'll post it here. there are a couple of articles in the wiki but they are pretty dense, too dense for me anyway.

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Old 12-01-2012, 12:41 AM   #3
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During boiling the pH drops by about 0.1 – 0.2 pH units from 5.3 – 5.5 pH to about 5.2 – 5.3 pH. This may be due to the addition of bitter acids from the hops, formation of acidic Maillard products, precipitation of alkaline phosphates or the reaction of polypeptides with calcium, liberating protons [Briggs, 2004].
http://braukaiser.com/wiki/index.php...ffects_brewing

ETA: Every bag of Rahr malt I've used has had a mash pH about .2 lower than EZ water would predict.
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Old 12-01-2012, 12:46 PM   #4
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I too have the same ph meter that you have Yooper. I have also had the same problems that you have encountered. I too will follow this as I was going to ask the same question to get a better understanding of ph. I think I will try to find a meter that actually solves problems, not creates them.

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Old 12-01-2012, 05:10 PM   #5
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Assuming it's accurate-ish, what is surprising to me is that the mash pH would be lower than the post-boil pH. That's why I'm wondering if it has something do do with the no-as-clear wort that I normally get.

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Old 12-01-2012, 07:59 PM   #6
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Ah, what indeed is pH? It is the negative logarithm of the activity of the hydrogen ion

"The quantity pH is defined in terms of the activity of hydrogen(1+) ions (hydrogen ions) in solution:

pH = − lg[a(H+)] = -lg[m(H+)γm(H+)/m°]

where a(H+) is the activity of hydrogen ion (hydrogen 1+) in aqueous solution, H+(aq), γm(H+) is the activity coefficient of H+(aq) (molality basis) at molality m(H+), and m° = 1 mol/kg is the standard molality." IUPAC definition.

That doesn't help much with understanding what pH is, does it?

Let's look at the brewing variable that is more important even than pH: temperature. What is that? The definition is even more confusing to a non scientist than the definition of pH. Yet we all know what temperature is: it's a measure of how hot or cold something is. We know that if it's 90 °F out we want to wear a short sleeved shirt and if it's 30 ° we want to wear a coat. Thus our notion of hot and cold is, in terms of the number we call temperature, relative to some standard temperature, say 70 °F, that we call, in this example, 'room temperature'.

It is much the same with pH though perhaps not so many know what the physical sensations of low and high pH are. They are sour (low pH) and bitter (high pH) taste. These physical sensations apply within a limited range of pH outside of which there will be tissue damage just as is the case with temperature. Again, as with temperature, there is a reference point: pH 7 which we call 'neutral' and is the pH of very pure water.

Temperature and pH are both parameters which influence the way in which complex chemical processes work. For the enzymes which catalyze the brewing reactions we want to work properly they must be in an environment in which both temperature and pH are proper. For an enzyme molecule to operate as an efficient catalyst it must be conformed to a particular shape. This requires that the molecules have a certain kinetic energy. If too energetic the molecule may vibrate apart so violently that a bond is broken and the shape forever lost (denaturing - what happens to the protein in egg white as it is cooked). The enzyme proteins are held in shape by electrical charges along their length. Changing the pH changes the distribution of these charges and thus changes the shape of the molecule as does heat (though the mechanism is different). Thus we can make cevice without cooking the fish through the use of low pH lime juice and often add vinegar to the water when poaching an egg.

Thus we must set pH in brewing if we want enzymes to work just as we must set temperature. How do we do this? The answer is by using acid/base pairs. An acid is a substance which gives up hydrogen ions and a base is a substance which takes them up. In considering brewing water the acid that gets talked about a lot is carbonic acid and the base is bicarbonate ion. In the reaction H2CO3 <---> HCO3- + H+ we see the acid (H2CO3) giving up the hydrogen ion (H+) to form the base HCO3- if we read from left to right. If we read from right to left we see the base, HCO3-, taking up the hydrogen ion (H+) to form the acid, H2CO3. Each acid/base pair has associated with it a value called the pK. If we know the pK for an acid base pair and the pH we can easily determine the relative amounts of that acid and base in a solution. If, conversely, we take pure water we can add acid and base from a pair with known pK in a particular ratio in order to make up a solution at a particular pH and which, in fact, tries to hold that pH. This is called a 'buffer'. Malt contains many buffering systems and water contains 1 (the carbonic bicarbonate one). When water and malt are mixed the pH of the mix is determined by the pH's of the individual buffer pairs (which depend on the relative amounts of acid and base and the pK) and the total amount of the elements of the pair (buffer strength). You can think of each buffer pair as a spring of length proportional to the pH and strength proportional to the stiffness of the spring (its thickness). If you hook those springs between two rail cars (and I choose this parallel because these buffers are called buffers by analogy to the railroad device which is used to absorb forces which tend to push together or separate cars) the distance between the cars will be determined by all the springs but the stiffer springs will have the most influence.

So think of temperature as something which controls the kinetic energy of molecules and pH as something which controls the electric charge on molecules and, as a consequence of this, controls the extent to which acids release hydrogen ions (that's why they are part of the formal definition) and bases take them up.

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Old 12-01-2012, 09:37 PM   #7
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Bumping to follow. Exposure to enough well written articles like this and some of it might begin to soak in. Thanks

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Old 12-02-2012, 11:43 AM   #8
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Here here! I'm glad I was drinking coffee while reading that. Thanks AJ. Now I'm pH testing my java

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Old 12-02-2012, 05:39 PM   #9
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I've never met a pH meter that worked under 500 bucks, the hand held ones are just terrible, I get them for free and I use paper instead.

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Old 12-02-2012, 05:53 PM   #10
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Even some of the under $100 meters work pretty well. They are not as temporally as stable as the more expensive units which requires that they be calibrated every 15 minutes or so as opposed to once per day or week but they are useable.

Apparently the Milwaukee's are not among these.

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