Author Topic: acidity, desired pH, and measurement  (Read 362 times)

Offline quidnunc

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acidity, desired pH, and measurement
« on: April 30, 2013, 11:25:55 AM »
Hi
As I have said in previous posts, I have a lot to learn about cheese-making and my current problem is about acidity.

As I understand it, acidity plays a major role in cheese-making and it is good practice to know how this develops, how to measure it and how to interpret those measurements.  Many of you speak of using pH meters but I want to go down the route of Titration to determine the acidity and how how it develops during the coagulation phase (I want to do it this way so that I can show my grandson how to carry out a titration). So my question is: is there anywhere on the forum that list the desired acidity levels for the various cheese types (either as pH or %) and also how does acidity affect the final product?  As always any help/advice will be much appreciated.


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Offline linuxboy

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Re: acidity, desired pH, and measurement
« Reply #1 on: April 30, 2013, 11:37:08 AM »
titration instructions: http://cheeseforum.org/forum/index.php/topic,2586.msg21615.html#msg21615
general guidance for continentals: http://cheeseforum.org/forum/index.php/topic,5816.msg46452.html#msg46452

What cheese are you trying to make? Have to tailor the levels to the milk and process and culture.

I keep meaning to write a post about buffering and acidity controls to consolidate the info in a single place. I'll try and get to it next week.
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Offline quidnunc

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Re: acidity, desired pH, and measurement
« Reply #2 on: May 01, 2013, 09:55:42 AM »
Hi
Thanks Linuxboy for your reply and the links you provided.  I apologise in advance for the length of this post but please bear with me.

I have read the discussion with Bobb and others your link sent me to and found it VERY interesting; it brought up a number of questions that I need answers to but as usual raised others.

In your answer to Bobb's question you said that the measurements were indicators to you. I assume by this you mean that you use the acidity reading to decide at what stage the make is at and what you need to do next, i.e. acidity is X so do Y. But this comes only with experience, something I am lacking at this time. I can only do what the instruction leaflet that came with the culture I purchased tells me to do and as these are voiced in very general terms it leaves me with very little insight into what is happening. Therefore question: If acidity is only part of what the curd is doing what else are you looking for? 

You go on to say that the whey is less acidic than the curd which suggests that it would make an observable difference to the final product, am correct in thinking this? GParenteau stated in his post that "In cheesemaking lactic acid is fairly important during the coagulation process as well as the texturizing of the cheese curds", so I take it from this that at some point in the acidification process I need take some action that will produce a required texture--soft, dry and crumbly etc?

Tomer 1 asked if there was a table and you provided an (updated) chart which is quite informative but I'm not sure what the terms O-type culture and NFM refer to nor do I understand why one has to stir at a specfic RPM. Of course, this part of the conversation may have strayed from the original question because you are now talking about calcium bondage breaking.

I take mhiil's point about keeping a record (and your comments) of of my progress which would be pertinent to me and my personal circumsatnces and working conditions etc.

Although I am making cheese purely for my own consumption, my fun is derived exactly from trying to be precise; my old-school education I suppose (I am 75).

The link to your article on measuring acidity I found particularly interesting and informative, it answered a number of points I wanted to raise, so thank you for that.

As to what cheese I am trying to make, that is a difficult question to answer at this time, for as stated above, I bought a culture and followed the directions. I have made two batches/makes; the first was smooth and creamy, like a thick yogurt, the second was much drier and crumbly even though I followed the same procedure for both (or so I thought). I have contacted the seller to enquire what cheese type the culture was supposed to make and await his reply.

Offline linuxboy

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Re: acidity, desired pH, and measurement
« Reply #3 on: May 01, 2013, 10:22:03 AM »
Quote
In your answer to Bobb's question you said that the measurements were indicators to you. I assume by this you mean that you use the acidity reading to decide at what stage the make is at and what you need to do next, i.e. acidity is X so do Y. But this comes only with experience, something I am lacking at this time.
mmm, true, I am more interested in what is going on behind the scenes and acidity is part of that. But even without experience with your milk and cheese, it does not take too long to be able to tell by establishing a baseline for what constitutes good outcome. For example, you use a starter, milk, and make cheddar cheese. And you follow the general best practices for a traditional American cheddar, which are wait for .015-.020 TA drop (not higher than .20 TA total) before adding rennet,  then wait another .02-.05 before draining, and start milling around .40-.50. That's for an American style. For British or NZ styles, the milk and terroir are different, so you have to make slight adjustments. See what I mean by indicators? There is a right answer, but you have to ask a very detailed and exact question.
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If acidity is only part of what the curd is doing what else are you looking for? 
It is not only total acidity, but also acidity over time. I am looking at the rate of acid development by the starter vs how much the milk is buffering it. If the starter activity starts more slowly, then falls off a cliff, or if the milk has high casein, I can't just use the base recommendations as is. I can use them to establish a baseline, and then do a few small scale trials to tweak the recipe to my milk and situation. The general parameters of most recipes are sound, but may not be optimal for your situation.

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it would make an observable difference to the final product, am correct in thinking this?
Eh, yes, but honestly, I don't think it makes a dramatic difference, so long as you are consistent. Measure the same stuff every time. If measuring whey pH, stick to whey pH. remembering the whey vs curd difference is more useful for initial recipe formulation when designing new cheeses to target specific texture properties from the rate and degree of casein breakdown.

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I take it from this that at some point in the acidification process I need take some action that will produce a required texture--soft, dry and crumbly etc?
Yes. acid breaks down the protein in milk. It breaks it down faster when milk is liquid (which is part of why we ripen before adding rennet and look for a specific acidity before adding rennet), and acid breaks down protein slower in curd, because the curd is "seized" up. Less motion, slower movement inside the curd bits. And you're balancing these factors... too much breakdown before rennet makes for a more crumbly curd. Too much breakdown before draining, same. But when milk goes to curd, it slows down the rate of breakdown because curd is a gel, no longer a liquid. At the same time, acid production starts increasing exponentially. So it's a trade-off game of balance.

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O-type culture and NFM refer to
o-type is standard cheddar type culture
NFM = nonfat milk

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nor do I understand why one has to stir at a specfic RPM
I did this in the lab. Stirring is to ensure even distribution of cells, medium, and waste products. Basically, reduces variability. It's a lab result, optimized.

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you are now talking about calcium bondage breaking.
This is the crucial piece to understand. Milk buffers acid through these bonds (primarily). And caseins are held together by these bonds (primarily).
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Offline quidnunc

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Re: acidity, desired pH, and measurement
« Reply #4 on: May 01, 2013, 03:49:24 PM »
Hi
Thanks for the response but before I answer let me get the information I requested from the supplier of the culture, at least then I will know if the results I got were what I should have got or not, then I wouldn't be floundering in the dark.


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Offline quidnunc

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Re: acidity, desired pH, and measurement
« Reply #5 on: May 06, 2013, 04:56:14 AM »
Hi Linuxboy

Well, as is becoming more prevelent these days, the request for information has been ignored by the supplier of the culture (I have had no reply).

This is the information that came with the culture.        

"The Freeze Dried Cheese Starter is an advanced blend of no less than four carefully selected bacteria cultures. It is an ideal general purpose culture, well suited to the manufacture of all forms of cheese- soft, hard, pressed, surface ripened etc, etc. It is also suitable for use in the production of buttermilk and many others dairy products that are available today".

So, as you can see, fairly general. It also suggests that I wouldn't need to buy different cultures because this one is suitable for all the types of cheese I would want to make (although it doesn't say how to do this). To make a soft cheese the instruction was:

1.Heat one gallon (4.5 litres) of milk to approximately 90ºC (194ºF) and then cool rapidly to 20-22ºC (68-72ºF).
2. Add two tablespoons (30ml) of starter culture solution previously prepared, and add 4 drops of pre-diluted rennet. Cover the container and stand in a warm area at 20-22ºC (68-72ºF) for 24 hours, when a good curd should have formed.

I assume the initial heating to 90 degrees was to ensure the milk was free from undesirable bacteria but I would have thought that store-bought milk would pasturised anyway.

I too am interested in what goes on behind the scenes and given what I have read have come to realise that acidity plays a major role, and yes, establishing a baseline is imperitive so I will make notes of everything when I try my next make.

The instructions that came with the culture say to add the rennet at the same time as the culture but from what you, and almost everyone else says, it should be added later as stated in your example for cheddar but if I don't follow the given instructions I can't establish a baseline for my bought milk and using the culture I have.

So, to establish a baseline for a soft cheese using this culture and taking your point about measuring acidity over time, my plan is to prepare the milk and add the culture and  rennet and measure the acidity level change during the following 24hrs. If I measured say every 4hrs during the day I could get a feel for what the RATE of acidification is (I realise that this is an exponential rise and therefore have to considering that I will be asleep for a good part of this period) and noting any visible changes in appearance. I would be measuring the whey acidity as I'm not sure if there is a method of measuring the curd by titration. I should then end up with a soft cheese.

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'too much breakdown before rennet makes for a more crumbly curd. Too much breakdown before draining, same'
so if I wanted to make a drier more crumbly cheese from the same culture I would delay adding the rennet until the acidity built up--to what?

Thanks for the time and benefit of your experience you have given me.

quidnunc