Acidity versus curd?

[tananaBrian]

Hi,

  Totally new and inexperienced here, but I have a couple of questions about pH versus the formation of a curd with rennet:

- Does a lower pH speed up curding, e.g. shorter time to clean break after adding rennet, or vice versa?
- Does a lower pH produce a firmer curd or softer?
- What is a valid range of pHs for achieving a reliable curd/clean break?
- If the curd is soft, not yet a clean-break, will it eventually get a clean break if you wait long enough?  Or if there are other factors involved here, assuming the milk is OK, what are they?

Thanks,
Brian

[linuxboy]

- Does a lower pH speed up curding, e.g. shorter time to clean break after adding rennet, or vice versa?

Yes, within reason. It's a function of acidity, but not a linear one. I.E. you might see a 15% faster curling going from 6.5 to 6.4, but going from 5.9 to 5.8 it's won't be a 15% increase.

- Does a lower pH produce a firmer curd or softer?

For what kind of cheese? Firmness of set is generally determined by available free calcium, casein quality and amount, PF ratio, rennet amount, time of set, and temperature.

What is a valid range of pHs for achieving a reliable curd/clean break?

Generally, you want to add rennet at a pH of 6.5 for cow milk.

If the curd is soft, not yet a clean-break, will it eventually get a clean break if you wait long enough?  Or if there are other factors involved here, assuming the milk is OK, what are they?

yes, usually time will take care of it. But you have to be careful because you need to balance the pH target at which you drain pH with the moisture-in-curd target for the cheese style. Meaning if you wait too long before cutting and stirring/heating, acidity might run away. Already explained the other variables.

[tananaBrian]

Thank you!  I saw a response from "linuxboy" and thought ..."Oh no!  It'll be over my newbie head!", but it wasn't.  My questions were intended to be general in nature and your answers were just what I was looking for.  I'm buying myself a pH meter for Christmas...  Hate to admit it, but I'm an engineer ...having visibility into the system would be great, at least more than I have right now and pH seems like the most logical first step.

Someone around here mentioned that when they visited Europe, that only one in 28 cheese makers used a pH meter ...my first thought there was "Well yeah ...they get a consistent fresh milk supply and use consistent processes, and I'll bet the DO own some fine thermometers!".  WE however get milk from the store and it could be all over the map from an age, quality, and pH perspective.  Just look at all the different expiration dates across town... I think a pH meter will be handy for producing more consistent cheese from a less consistent milk supply.

Brian

[linuxboy]

They also make 1-2 cheese types, day in and day out. You get a feel for slight variances with that much repetition.

I try to keep my writing accessible. Sorry if I go off sometimes; I know it's often excessive. Hard to stop myself from giving the "exact" answer.

[tananaBrian]

Actually, the posts that I've read have been quite informative even if some of the material were things I had not heard of before.  That's fine with me ...sort of like mental bookmarks that I can look into more later.

Brian

[Gürkan Yeniçeri]

Linuxboy, I like those "exact" answers, please keep them coming.

For the storebought milks, I was always thinking that they would be somewhat standardized and always same level of fat and pH and therefore you don't need a pH meter (just obey the times like floculation and temperatures). But if you are getting fresh milk from a friend than its another story, you must have a good pH meter and a good thermometer as you do not have control over what the cow eats everyday. Am I wrong in this assumption?

[linuxboy]

if milk is fresh, the pH variance should be minimal for all mixed milk, raw, pasteurized, etc. old milk has more acidity due to lipolysis and bacterial growth/lactose conversion.

[justsocat]

I get the fresh raw cow milk from the same farm for last three months. And pH range vary for 0.25. Wide range. I can't manage without pH meter.

[tananaBrian]

Somewhere on this forum, I read about someone having their milk work fine, but a week later milk from the same purchase didn't, and I thought the likely culprit was a dropping pH during the extra week.  With all the different suppliers, and different pasteurization methods and temperatures, and shipping distances, I would expect to see variation... But of course, I'm in Alaska and the only milk made locally is apparently ultra-pasteurized and useless.  ALL of our milk has traveled a great distance to get here (about 2000 miles minimum ...on sea barges and trucks).

Brian

[linuxboy]

The more complete answer is that it depends. When commercial milk is mixed, it tends to come to an average of about 6.68. Raw milk when mixed from a large herd tends to be around 6.7. This is when fresh. But, there are seasonal variabilities even when large amounts of milk are mixed.

When dealing with smaller volumes, or individual animals, there can be significant variability based on health, feed, seasonality, stress, etc.

Bulk milk = averaged values = generally more consistency in fresh milk
Farmstead milk = depends on feed, health, etc because of fewer animals.

[Gürkan Yeniçeri]

Ok thanks Linuxboy,

One more thing to ask. I think my pH meter is reading it wrong. I have got some fresh milk last weekend (after 3 weeks of calfing, so colostrum levels may still be a bit high) and the pH was reading 7.3. I am guessing this was related to somatic cell count but I have no means of measuring this or my pH meter (I calibrate before each use) is off. What should be the titratable acidity if I go that way of measuring it (.1N NaOH).

PS: OK this sounds like sci-fi. like Rodney at Stargate Atlantis talking to Samantha Carter. But if Stargate Atlantis has got Rodney we have Linuxboy on the cheesemaking science 

[linuxboy]

7.3 is either extraordinarily bad milk, or meter error. SCC would have to be truly extreme, something above 1 million to get there.

Colostrum is mostly gone after 7 days. After 3 weeks, should not be present.

TA of fresh milk should be ~0.15.  When you get above .18, milk quality is questionable. This is for cow milk.

[Gürkan Yeniçeri]

Noted. Thanks Linuxboy.

When you say bad, in what sense? The milk still coagulates well and things are looking normal during the draining and pressing. Also knitting is quite good. I think pH meter is off a bit.

If I calibrate the pH meter with 7.0 solution and when the calibration is done, dip it into 4.0 solution, I should be reading 4.0 shouldn't I? This should tell me if the meter is off, doesn't it?

[Sailor Con Queso]

Gurkan, Sounds like issues with your pH meter. Your pH meter should have a 2 point calibration, so you should calibrate at 4.0 and 7.0 before every make. If your meter can only be calibrated to 7.0 then is not very accurate and it will always be unreliable.

[linuxboy]

bad here meaning mastitic. agree with Sailor, meter issue.