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[Cheese making help] Lower pH with citric acid

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  1. Feb 26, 2018 #1
    I made an account to ask this. I have looked and could not understand any of the formulas I came across. I even looked for calculators, but did not understand how to use them.

    Milk has a pH of 6.5 to 6.7 (lets use 6.7)

    And I wish to lower the milk's pH to 4.9 (as an example)

    How do I calculate the citric acid amount needed to lower the pH for my needs?

    Thank you for your time and help.
     
  2. jcsd
  3. Feb 26, 2018 #2

    HAYAO

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    Homework section, maybe?

    pH = -log10[H+] right?

    If you know the pKa of citric acid, and the volume of the milk, then you can estimate how much citric acid is needed (of course, under the assumption that we are treating the milk as ideal solution and no special interaction occurs between the substance in the milk and citric acid).
     
  4. Feb 27, 2018 #3

    Borek

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    Not enough information to answer the question, best approach is to do it by trial and error.

    Because of the buffering effects of various milk components amount of citric acid depends on the exact composition of the milk, it can't be easily calculated just from things like initial pH and citric acid pKas. These can be used to estimate the minimal amount of the citric acid required, but such an answer can be orders of magnitude wrong.
     
  5. Feb 27, 2018 #4
    I would first need to know what this is

    1 US gallon, or 3.7 liters

    that is all I would know
     
  6. Feb 27, 2018 #5
    okay...then what else would you need to know?
     
  7. Feb 27, 2018 #6

    jim mcnamara

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    Let's try a more helpful direction.

    First off, when you add citric acid (or vinegar) to milk you get curd. You can also use rennet which is a better choice because it does not mess up the pH radically.
    If you can me EXACTLY what you want (not pH) to make - i.e., the answer is like "farmers cheese", "cheddar cheese" then I can help you. At least to start. BTW, many types of cheese require special curing conditions with special varieties of bacteria/fungi present in the curd. So Manchego cheese, for example, is not going to happen easily. It requires sheep milk. Camel milk, as well as raw milk (unpasteurized, and unrecommended) are also interesting. In the sense of they can all be hard to get.
     
  8. Feb 27, 2018 #7
    I am doing acid-set cheeses, so rennet and cultures are not required.
     
  9. Feb 27, 2018 #8

    jim mcnamara

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    Okay, for paneer, chenna, table cheese, most acid set cheeses:
    This works for whole milk - do not use UHT pasteurized milk (long expiry date, in the US use milk from local SMALL dairies). I personally avoid raw milk for safety reasons.
    [comment]
    BTW is there some reason why you cannot give us real specifics on your ingredients or exactly what you want? This is a little like going to the car repair place and telling the repairman 'my car is not working right, fix it.' Then walking away. So. We have to play 20 questions. Detailed questions get great answers without playing games. I'm just doing one decent answer. For example, are you using lemons, dry citric acid powder, or liquid citric acid? Here goes:
    [/comment]
    1 gallon whole milk - room temperature works faster.
    10g dry citric acid powder dissolved in 125 ml (~½ cup) water.
    Stir well, let stand for 30 minutes, separate with a cheese cloth.
    PS: the whey is completely edible, if not kind of tangy from the citric acid.

    The reason you cannot get a perfect pH has to do with the chemical nature of milk. It is not a perfect constant and some milk may have more less of naturally occurring chemicals (buffers) that can affect final pH. The above always works. If you MUST have a precise final pH you need a pH meter. If you can live with an approximate pH you can get specialty pH test strips fro the acid range you need - ex: 4.0 -> 7.0

    Brewers (beer makers) use these test strip: https://preclaboratories.com/product/beer-ph-test-strip/

    Dunk them in the milk after stirring, start with less than the full amount of citric acid solution, add it in increments, stir, then test again. Keep going until you get where you need to be.
     
  10. Feb 27, 2018 #9
    I did say what I'm using. I'm using citric acid. I'm not making my question complicated. In fact, you're making it more complicated on yourself by assuming I haven't even made cheese before.

    I asked how to calculate it. It doesn't matter if the milk can vary or not. I can either figure it out, or just use 6.7 as my base.

    When someone says use 10 grams or use 1 teaspoon, that doesn't help me. Why that much? I have followed these "recipes" and the curds vary way too much for it to be blamed on the milk's varying pH.

    I want to calculate it myself and not rely on these guesstimated measurements of acid.
     
    Last edited: Feb 27, 2018
  11. Feb 27, 2018 #10
    I looked this up via PubChem

    pKa = 2.79
     
  12. Feb 27, 2018 #11

    HAYAO

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    That sounds like a bit disrespectful to people who are generous enough to help you. Try to tone it down a little. Relax.

    Search google for "pKa" and the first result gives you the right result for what pKa means. You searched and pKa was 2.79.

    pKa = -log10Ka = [A-][H+]/[AH]
    pH = -log10[H+]
    Molar mass of citric acid: 192.12 g·mol−1
    You have 1 gallon of milk.

    These four information provides you enough information for the calculation. But like I said, this calculation is valid under the assumption that no interaction occurs between citric acid and substance in the milk (such as buffering). So like Borek said, it will going to be a very rough estimate (or not even an estimate), and not so reliable.
     
  13. Feb 27, 2018 #12

    Borek

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    We already told you that exact calculations are impossible, as milk - being a natural mixture - doesn't have a constant composition. In effect the amount of citric acid required will be sample dependent, and the only sure way is to add acid till pH is what you want it to be.

    It will turn out that the acid is typically similar and that's where the recipes like "10 g of citric acid per gallon of milk" come from - but they are typically based on experiment, not on calculations.

    Besides, I can show you equations required - but you already said that the ones you found are too difficult. The ones I can list won't be easier, these calculations are not trivial and require a bit of chemical and math knowledge.
     
  14. Feb 27, 2018 #13

    jim mcnamara

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    Your assumptions are wrong. If you are having curd problems it is not just milk pH. I would cite some technical papers here, but it may not help.

    Here is a citation that I'm sure you can read, and that disputes what you said:
    https://www.sciencedirect.com/science/article/pii/B9781845690601500089.

    NB: Milk varies and it is important, so is temperature, so is pH, pasteurization, etc. If you do not believe me, that's okay.
    pH of fresh good quality raw milk range ranges from pH ~6.3 to 6.4, but milk cointains lots of buffers - chemicals that resist pH change - which is one of your issues. The buffer chemicals can vary. https://www.slideshare.net/farhana25/measuring-the-ph-of-milk. Different levels of pasteurization change pH.

    You can calculate pH for pure water. In your case it is: use test strips. Or. If you are doing this to make money buy a pH meter. That is what professional dairies use.

    So if you get nothing else out of this - you cannot accurately predict the pH outcome of adding citric acid to milk unless you completely control everything else beforehand. Including the starting pH. Can't help you any more.
     
  15. Feb 27, 2018 #14

    jim mcnamara

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    Since we answered with known science this thread has run its course. Thanks for participating
     
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