milk pH, more specifics?

[Susan38]

With my new pH meter I am finally able to start monitoring pH of my raw Jersey/Brown Swiss milk.  I've read about normal pH ranges, and also about how temperature affects the pH reading.  For example, Caldwell demonstrates in her pH video that the pH can drop about 0.1 when measuring milk at 40 F and ~90 F, respectively.

Unfortunately, most pH numbers are presented without corresponding temperatures.  So when I read that "normal milk pH is between 6.5 and 6.7", at what temperature is that?  And on another note, is that range specifically 6.50 to 6.70 or 6.50 to 6.79? 

It's commonly stated that if pH is above 6.7 then that might mean the cow has mastitis.  But then, there is no reference temperature associated with that number. Caldwell mentions in her book to be concerned about mastitis if milk pH is 7.0 or higher.  Then I read a scientific dairy experiment where pH was measured on raw milk and it was 6.8-6.9 @ 75 F and it was considered "Grade A milk".  So I'm finding different numbers for the threshold of "suspected mastitis".

The reason I'm digging deep into this, is that my milk is measuring somewhere around 6.83 @ 40 F, and 6.73 @ 90 F.  I'm not sure whether or not to be concerned, as these numbers may (or may not?) be in the neighborhood of what might flag "suspected mastitis".

I'm also wondering if environmental factors, such as high alkaline soil and water, can influence the milk pH.

Any thoughts on any of this from you dairy folks out there would be most appreciated. 

[MacGruff]

Hi Susan,

I noticed that no one replied to your post, and since I do not have my own cows, or source for fresh milk, I cannot contribute any wisdom to your quest either. I do, however, have a related question:

I am trying to master making Tomme. I am relying on supermarket milk. My second attempt at making it us under way and is not too successful, but I have been diligently measuring pH levels and posted them elsewhere. One of the comments made was that the starting pH of my milk at 5.92 seemed rather acidic (this was at a temp of 58 degrees). By the time I got the milk up to 88 degrees, the pH dropped to 5.80.

Two days ago I started another make, but sourced my milk from Costco. At 88 degrees, the pH of the milk was 6.04.

As you can see, I am seeing much more acidic milks from supermarkets than you are.

In both of my makes, I calibrated my pH meter before starting the makes so I am fairly sure that my readings are accurate to the extent of the meter.


Is this a reflection of being Supermarket milk? Time of year? Any ideas?

[Bantams]

Those values are so far off from the normal range that either the milk is starting to sour (possible if it's been in the fridge for a while, though doubtful), or your pH meter is having issues. The fats and proteins in milk can make it tricky to use a pH meter - there are milk/cheese-specific meters for that reason and I wonder if a generic meter is getting clogged with fat/protein and giving poor readings. 

I know the original question is old, but I've read 6.7 is the typical pH of raw milk. If I had a high reading I would check the SCC of the milk and check for ketones.
Below 6.6 and I would revisit handling/chilling and sanitation procedures. I do know that the pH will change slightly after pasteurization, but I can't remember which direction... Just 0.05 or so.

[MacGruff]

Thanks, Bantam.

As you saw, it's what I've seen with two different sources of milk out here.

Just to be clear, I've calibrated my pH meter before each make using distilled water. Also, the milk's expiration date was more than a week away (the one I used three days ago was 19 June).

What can I say? I wish I had a better source around here, but I got what I got...   

[Susan38]

Hi All!  I've been restricted to brief lurking here for quite a while now due to time constraints (but I do have lots to report at some point on recent cheese experiences!)  Starting back in with this subject.  Two points:

1.  Milk.  Thanks Bantams for your input.  Since my original post I have had the pleasure of trying out several different milks.  My original source, documented above, had the high-end pH (6.7-6. consistently.  Next I tried Straus (store-bought) and it was consistently in the 6.65 area.  I also tried Sprouts brand P&H milk and it too was at 6.65.  Now I'm with another local source with Holstein and Jersey and it's consistently in the 6.55 area!  I have been suspecting cooling issues with this source and with your comment, Bantams, I will be looking in to this issue further.  I also have a source of Dutch Belted, pasture-fed milk and it's pH is in the 6.6 range.  All this to say, I have yet to experience milk pH's as low as what MacGruff is experiencing...leading to my next point.

2.  pH meter.  MacGruff, I too am suspicious of your milk readings and am thinking it is not the milk, but your pH meter.  I'm not sure what you mean about calibrating with distilled water...are you using the pH 4 and 7 buffer solutions to calibrate, or using distilled water?  If the latter, that could be the issue.  Otherwise, have you cleaned the probe with warm soapy water to make sure there is no oily residue from the milk interfering with the readings?  Have you searched the Equipment board for methods to clean and/or reset your pH meter?  If you've tried all those things and are still coming up with off readings, it is possible that you have a "lemon" that is not functioning properly, in which case you should contact the manufacturer for further guidance or replacement if necessary.

Susan38

[mikekchar]

Yes, calibrating with distilled water won't work.  While the pH of distilled water is 7.0 *any* kind of contaminate will wildly swing the values.  Specifically, any kind of calcium salt will drive the pH up quite a lot.  I suspect that's 100% your problem.  As Susan38 said, you need to get pH 4 and pH 7 "buffer solutions".  A buffer solution is a solution that has salts in it which essentially "absorb" and other changes to the pH.  You can add acid to it, or calcium salts and it won't budge.  Pure water will swing like crazy with even the tiniest amount of anything in it.  You should be able to buy the buffer solutions at the same place you bought the pH meter.  Then you calibrate for both the pH 4 solution and the pH 7 solution (I forget which one you do first -- it's been years since I had a pH meter).

[scasnerkay]

I have access to milk from two cows. I have taken the pH meter to the farm in order to test, but usually I just test before starting my make. And usually the milk has never been refrigerated, I just bring it home and start.
Depending on where they are in their lactation cycle and depending on the individual cow, there can be quite a bit of variation. I find a gradual increase in pH going from early lactation to late. The range is generally 6.5 to 6.75. This would be at about 80 to 90 degrees. A long time contributor to the forum said he refuses milk in his commercial operation if it is coming in at 6.8.

Purchased store milk is carefully standardized for protein, fat, pH, and probably other factors as well. Every time I have used it, it measures very close to 6.65.

I periodically run through a multi step cleaning process of the pH meter, and do a hard reset. I calibrate before use at 7 and then 4 using the standardized solutions and rinsing with tap water then blotting dry before using the next solution.

[MacGruff]

Ok. I hear you. I went on Amazon and ordered 4.01 and 7.0 pH solutions to calibrate the meter with.

Up till now, I've been washing the tip off with warm soapy water, wiping it off, and then putting it in a small amount of distilled water - figuring it was about 7.0 pH. It was fresh distilled water, not adulterated in any way.

By the way, Tomme #3 is in the cave, being flipped every day.

[Susan38]

I was very surprised when I first got my pH meter and measured distilled water straight out of the bottle and it was at 6.3.  Then even more surprised with my filtered tap water (filter removes all of the minerals) and it's consistently at 5.5-5.3!!  (Which made me realize my understanding of water chemistry is quite limited, ha ha).  There's a post in the "washed curd" cheese board about this in further detail.

I remember a post somewhere in the equipment board about distilled water not being recommended for use with pH meters...can't remember exactly why but it's not good for the electrode or something like that.

Glad to hear you're on your way to get buffer solutions...let us know if that solves the meter problem or not.  And congrats on your Tomme #3 make!

[Bantams]

My new pH meter just came and the instructions say to never store the probe in distilled or deionized water. I'd say that was almost definitely the issue.