High pH and poor coagulation but negative on mastitis test!

[scasnerkay]

My cheeses are generally made from the milk of one cow at a time. Henrietta’s milk usually is quite nice. But in the past 3 weeks her calf decided she wanted to nurse off a different cow! The result was way too much milk in the udder over several days, up to 6 gallons, on the AM milking which is huge for a small Jersey cow.
CMT paddle test is negative, and samples sent to be tested were also negative.

The milk pH is HIGH, I am testing 6.8 to 7.05.
Progression of pH drop during make is very slow initially, and then in the press too fast!
Rennet coagulation is very slow, taking at least twice as long as usual for the proportions used normally.
Coagulation is softer with a poor clean break.

Anyone know what type of problem other than mastitis might be causing these problems??

[mikekchar]

Generally no idea, but:

Progression of pH drop during make is very slow initially, and then in the press too fast!

This means that the milk is buffering the pH.   It's like adding vinegar to solution with baking powder in it.  The solution has a particular pH, when you add the vinegar, it is neutralised by the baking powder, but the pH doesn't move.  When you use up all the baking powder, the pH moves incredibly quickly with just a little vinegar.

For milk, the main buffering agent is usually calcium phosphate.  Most calcium phosphate is bound up in the "casein micelles" (bundles of milk protein), but some of it is dissolved in the milk.  As you add acid, the acid reacts with the calcium phosphate, neutralising it -- the pH doesn't move.  Once you use up all of the calcium phosphate, the pH drops.  However, as the pH drops, the casein micelles "relax" and release more calcium phosphate into the milk.  It takes a bit of time for the calcium phosphate to get into solution, so you end up having the milk pH slowly progress down:  You add acid.  It neutralises the calcium phosphate in solution.  You add more acid.  It adds more calcium phosphate to the milk.  You add more acid.  It neutralises the calcium phosphate.  You add more acid.  It adds more calcium phosphate to milke.  Etc.

The rate the pH drops depends on the rate that you are adding acid and the rate that the calcium phosphate is dissolving in the milk.  If you add acid quite quickly, the pH drops quickly, but the *rebounds*.  You will see some threads where people talk about their pH going *up* over time and wondering why that's happening.  It's actually as a result of the milk acidifying too quickly at the beginning.

So my *guess* is that whatever is causing your problem is also degrading the casein micelles (milk protein).  This is allowing them to release calcium phosphate more quickly than they would otherwise.  That would account for the increased pH at the beginning (more calcium phosphate in solution) and also for the high buffering capacity followed by you completely running out of calcium once it's in the press.

Maybe take a look at the feed.  I *think* that problems with silage can cause problems like this, but I'm not sure.  Definitely not my field of experitise (barely ever even seen a cow up close in my life).

[Bantams]

What tests did you run on the milk? Do you have SCC counts from a lab?

[scasnerkay]

I am a volunteer at the farm. The farmer sent the milk to two different labs to be tested. One came back slight positive in one quarter, the other test came back all clear. So today she sent out samples again.
I know mastitic milk shows high pH and changes the casein micelles. But it seems odd in the presence of negative test results.
I wondered if over stressing the udder could cause changes in the milk quality. And I wondered if milking more often might resolve the problem.

[Bantams]

It sounds like the farmer sent off samples for a culture, and received one negative result and one slight positive (a somatic cell count would provide numerical results, not negative/positive).  A culture (or PCR DNA test) is used to determine which mastitis strain is affecting a quarter, but it doesn't actually tell you definitively if there is mastitis or not.

Unfortunately both false negatives and false positives are very common, dependant on the particular strain (some die off before inflammation/mastitis is even apparent, only 16 common strains are cultured for), etc.
While those results are valuable to the farmer (so they know what  type of treatment the cow might need), they don't tell you a whole lot about the overall milk quality.

The test that would be most useful to you as a cheesemaker is the SCC (somatic cell count). This is usually performed by a DHIA lab and only occasionally by a lab that does cultures. 
The SCC can be elevated for many reasons - mastitis, stress, udder injury, stale milk from incomplete milking, late lactation/low production, etc - and can really impact milk quality/cheesemaking (in the ways you described).
The CMT threshold is about 250k, which shouldn't be high enough to affect cheesemaking, but I've heard of cases where it really didn't show a positive despite a SCC higher than that. So I encourage you/the farmer to send off for SCC. As a bonus the lab will also send butterfat, protein, lactose, etc values. 

The fact that the cow's own calf prefers to nurse from another cow tells me that there's likely an issue with the milk (calves dislike stale or mastitic milk) - this is very unusual behavior.

[Susan38]

I am so very interested in several points of this conversation, that I would like to relate some of my own experiences related to the subject, as well as ask a few questions that have been lurking in my head for several years now.  I have been using milk from several farmsteads, each with a bit of a different management/feeding system.  My questions/issues stem mostly from those managing as "grass fed" milk, keeping calves on half of the day, removing them half the day then milking once a day.

The milk pH is HIGH, I am testing 6.8 to 7.05.
Progression of pH drop during make is very slow initially, and then in the press too fast!

I have been consistently having this problem.  So much so, I have sort of come up with a work-around.  During the initial ripening, if the pH doesn't drop, I just proceed as if it has.  I know darned well in the end I'll be chasing the pH so it doesn't get too low anyhow.  (It's interesting to note the farmstead that is feeding grass, alfalfa, and grain mix with once a day milking has a pH consistently at 6.5-6.6, while the "grass fed" cows have pH's more at 6.7-6.9, sometimes close to 7.)

The SCC can be elevated for many reasons - mastitis, stress, udder injury, stale milk from incomplete milking, late lactation/low production, etc - and can really impact milk quality/cheesemaking (in the ways you described).

Wow.  This is a revelation to me, especially the "stale milk from incomplete milking" and "low production".  I will have to check and see exactly what some of the milking protocols are on these farmsteads.  Could it be that they are only milking 2 quarters and leaving 2 quarters for the calf and that can result in "stale milk"?  Since I'm not the person milking the cow, I have no idea.

Right now I'm dealing with "grass fed" milk where the cow has low production...I'm guessing she needs more nutrition to produce higher quality milk, but for right now the milk has very low solids, not much cream and what is there seems to have low solids too.  It makes for runny yogurt and very low yield, high moisture cream cheese with curds that do not set up well.  But the flavor is nice and clean and makes for good drinking milk!

On the other end of the spectrum, milk I've used from a Jersey cow on the more traditional dairy diet with grain, etc. has so much milk solids and heavy, yellow cream that I have to back off on the rennet amount in a cheese recipe, otherwise the curds get way too firm, too fast.

So it has been fascinating to try all these different milks, but it does steepen the cheese making learning curve quite a bit.  I may go to using Straus milk to make cheese for a while so I can have more of a consistent baseline to start the process out with and go from there.

The remaining question is, can a good cheese making quality milk be produced from a primarily grass-based (no or very little grain) diet?  Or does it depend on the breed of cow, etc.?

[Bantams]

The most annoying side effect of share-milking (cows milked by humans as well as nursing their own calves) is the poor letdown that occurs. Letdown is the hormonal response to udder stimulation - the milk that is stored in the upper portions of the udder is "dumped" into the cisterns, where it flows out readily during milking or calf nursing. 

On a conventional dairy (not share-milking), the cows commence letdown when the milker preps/cleans the teats. Letdown occurs 60-90 seconds after the start of udder prep, and lasts for just 5-8 minutes. After that time the only accessible milk is what remains in the cistern (just a quart or so per quarter). 

The vast majority of the cream is contained in the hind/last milk, achievable only with a good letdown and complete milkout. 

When a cow is raising her calf, despite the best preparations and low stress milking environment, she will not letdown for anyone but her calf (for most cows; there is the rare exceptional cow).

The farmer has several options to try to manipulate her into letting down during milking time.
Some give a shot of Oxytocin at each milking (not recommended, and surely a violation of drug use).
The most common strategy for those with just one or several cows is to separate the calves overnight (so calf will want to nurse, and cow has a full udder in morning), then bring the cow into the parlor, prep her, let the calf nurse either right before or simultaneously with the milking process, then reunite the two. 
Because the calf is nursing, she'll have a good letdown and the farmer will get their share of the milk (and cream!)

Larger farms that keep calves on the cows simply milk as usual, getting a puny amount of skim milk for 4 months or so until the calf is weaned. Because the herd calves on a seasonal basis and some of the calves are sold right away, only 5-35% of the herd is share milking at any given time. The milk in the bulk tank is balanced out by the other cows who are letting down fully (no calf anymore) and many in the later stages of lactation so giving more cream naturally. 

That said, many small farms either don't know how to achieve optimal letdown or don't care enough (or it's too much work/too stressful - can be very stressful to separate the cows and calves every day) and so they just settle for having mostly skim milk until the calf is weaned.

So I really believe what you're experiencing is not the difference between different diets, but a vastly different management style and the calf-share operation is not getting a good letdown at milking time.  They really should not be selling that as "whole" milk...

Straus has wonderful products - I would definitely give them a try!

Just to be clear, dairy cows are bred to produce an excess of what the calf needs. So she still needs to be milked once or twice daily. Otherwise the calf will favor one or two quarters and not touch the others. The cow will then develop mastitis without intervention (and can die if not treated).

[Susan38]

Thanks Bantams...mystery solved.  My only previous experience is on a commercial goat dairy where kids were immediately removed from does, so did not have milk letdown issues.  I had no idea about letdown and that most of the cream comes at the end of the milking.

Still trying to fully understand about the stale milk...is it from not completely milking out the "cistern" area, or is it from cow not letting down milk and that is the milk that gets "stale"?

I will have to find out and report back the management story on the Jersey and Holstein milk I have access to at times...more conventional dairy ration, share-milked, but with tons of cream and pH is in the 6.55-6.65 range.  Wonder if they are letting the calves nurse right before they milk, or if they have other tips/tricks that result in successful whole milk.