Hi all,
Last night I accidentally heated my milk containing powdered starter culture + Blines to 50c. I 'm assuming this killed the culture? I decided to add some rennet once it had cooled and after an hour I got a clean break. I decided to leave it for a few hours to help reduce the PH but it only dropped to 5.2. Am I right in saying this is low because I killed my culture which usually breaks down the milk sugars to lactic acid? Is it worth pressing the curds, after all its the lactic acid that helps flavour the cheese right? The more acidic the better flavour?
And while I'm on this subject, when we talk about the PH curve, is it best to press and salt as soon as the cheese hits an ideal PH say 4.5 (depending on which cheese you are making)? I have a feeling my curds were sitting at PH 4.2 for a number of hours which would upset the curve? Any info on PH curves much appreciated!
Thank you
Quote from: steve brown on September 07, 2010, 10:25:42 AM
Hi all,
Last night I accidentally heated my milk containing powdered starter culture + Blines to 50c. I 'm assuming this killed the culture?
Usually not all of it is killed at 50C. You're talking about Lactococcus or something else?
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I decided to add some rennet once it had cooled and after an hour I got a clean break. I decided to leave it for a few hours to help reduce the PH but it only dropped to 5.2. Am I right in saying this is low because I killed my culture which usually breaks down the milk sugars to lactic acid?
I don't understand what you're asking. Starting pH is usually 6.5-6.8. If you're at 5.2, then there's active bacteria producing acid.
QuoteIs it worth pressing the curds, after all its the lactic acid that helps flavour the cheese right? The more acidic the better flavour?
Not at all. Lactic acid helps to preserve cheese. Cheese flavor comes from
1) Protein-protein interaction
2) Peptidases and proteases in the cell wall and cell membrane that help with protein catabolysis and peptidolysis
3) Natural flavors and enzymes in the milk that lead to flavor and aroma formation
4) Sugar glycolysis after press
5) Fat breakdown via lipolysis
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And while I'm on this subject, when we talk about the PH curve, is it best to press and salt as soon as the cheese hits an ideal PH say 4.5 (depending on which cheese you are making)?
This all depends on the cheese style and what you're trying to accomplish. Generally, you need to balance drain pH, press pH, demoulding pH and salting/brining pH.
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I have a feeling my curds were sitting at PH 4.2 for a number of hours which would upset the curve? Any info on PH curves much appreciated!
Not sure what you're asking. A curve happens by itself as the bacteria work. "upsetting" or modifications may change somewhat due to temp, but not sure what you want to know.
It dropped to 5.5 after 12 hours, usually it drops to 4.5 so I thought maybe it had heated, started to break down the sugars but then because of the high temperature had stopped doing its job at 5.5.
So when I mention upsetting the PH curve this is what I imagine it to be like, I maybe wrong as this is new to me and I'm trying to work out in my head what PH curves are all about. So when the culture is added the curve drops from say 6.5 to 4.5, and when its pressed and salted the curve increases again so you get this nice up and down balanced curve. If the curds were left at 4.5 for a number of hours then the curve would flatten for say 7 hours before increasing again when pressed and salted. Is this what a PH curve is all about?
Ok, woah, let's take a step back; I'm still lost. pH doesn't go up after salting. pH is a measure of the relative acidity in solution, meaning the H+ ions. Acidity is important for two reasons (two big ones, anyway). One, in lactic cheeses where milk casein has a negative charge, the acid buildup (lower pH) leads to the destabilization and coming out of solution of the caseins. In rennet cheeses, where the k-casein is cleaved and then curd is formed, the acid buildup is important because it removes calcium from the micelle. Meaning you have this complex casein "thing" held together by colloidal calcium "glue", and if that glue is removed by acid, it influences the character of the cheese. A swiss will have most of its calcium in tact, whereas a cheddar will not. That's why you drain the whey from cheddar at a lower pH (6.0-6.1) and also let the acidity build up some more afterward.
So that's acidity. The pH curve is the measure of acidity over time. It's a downward sloping curve whose speed of increase changes due to the activity of bacteria. This curve is important because you need to coincide time and acid buildup in your cheese in order to hit various pH targets at critical decision points, such as whey drain and salting/brining. To hot those targets, you balance the amount of culture with the temperature. As you add a little bit of culture, you introduce bacteria. Bacteria have distinct phases in their lifecycle. Those phases start with a lag phase, during which bacteria eat, are selfish, keep to themselves, etc. After this, you have a growth phase where bacteria will grow rapidly and party and split every 15-25 minutes, AND they will produce acid. Then there's a maintenance phase when the bacteria will stop multiplying and just produce acid. This is really important because it is this that makes for a pH curve. At first, there are not many bacteria, and you have a slow start... the pH does not decrease too much, maybe .1 in an hour. Then as the bacteria get going, the acidity really builds up. The acidity then stabilizes as bacteria run out of food or the environment becomes not very conducive to rapid growth, usually due to excess acid buildup.
Make sense? The curve is about how active bacteria are at specific temps. The slope of the curve will differ based on strain and temp, and you need to know this to time everything properly.
Quote from: steve brown on September 08, 2010, 10:50:43 AM
It dropped to 5.5 after 12 hours, usually it drops to 4.5 so I thought maybe it had heated, started to break down the sugars but then because of the high temperature had stopped doing its job at 5.5.
So the pH was already 5.5 at the end of your heating? Or you heated and waited and it kept dropping? If it kept dropping, there's viable bacteria there, just not that many. You stretched out your pH curve because effectively, heating is like adding 1/50 of the right amount (or some other similar small amount).
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So when I mention upsetting the PH curve this is what I imagine it to be like,
Like what? Like stretching it out so the drop is really slow? That's true, but I wouldn't call it upsetting. Causing swings is upsetting. Like if you added baking soda or lye to the milk to increase pH, that would be upsetting. You just slowed everything down.
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I maybe wrong as this is new to me and I'm trying to work out in my head what PH curves are all about. So when the culture is added the curve drops from say 6.5 to 4.5, and when its pressed and salted the curve increases again so you get this nice up and down balanced curve.
You mean in the cave, the pH increases? Well yeah, but that's not because of bacteria, that's a good part due to ammonia. Let's ignore this for this discussion; it's an entirely different mechanism. The way you have to think about pH for cheese is that it has to do with the number of bacteria creating acid, at a certain rate due to favorable or unfavorable conditions (temperature), over a specific period of time. And the rate of that acid development varies with available food, environment, and phase of bacterial life cycle.
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If the curds were left at 4.5 for a number of hours then the curve would flatten for say 7 hours before increasing again when pressed and salted. Is this what a PH curve is all about?
No, it would not increase when pressed and salted. In just about every cheese, pH will drop just a little after salting. For example, in cheddar, you salt at around 5.4. By the morning, the cheese is 5.0-5.1. Recent studies have shown that lactococcus will continue to produce acid and metabolize sugar even after death.
In rennet cheeses, where the k-casein is cleaved and then curd is formed, the acid buildup is important because it removes calcium from the micelle. Meaning you have this complex casein "thing" held together by colloidal calcium "glue", and if that glue is removed by acid, it influences the character of the cheese. A swiss will have most of its calcium in tact, whereas a cheddar will not
So, the acid produced by the bacteria removes calcium which influences the character. So if Swiss cheese has most of its calcium in tact this means that its pressed and salted at a higher PH level that Cheddar which has has less calcium in tact? So is this the reason why some curds are slightly more 'rubbery' and some are more 'sticky' ? Is that the calcium glue you mention or is it simply because there is more or less whey in the curd?
That's why you drain the whey from cheddar at a lower pH (6.0-6.1) and also let the acidity build up some more afterward.
Sorry if this is a simple question but why drain the whey? I have read recipes that call for draining but I thought this was done so that the drained whey could be heated and then added back to raise temperatures.. Is this correct? Raising temperature will speed up bacteria growth that will then produce more acids which are needed for Cheddar like you mentioned.. Speeding up the PH curve?
Then there's a maintenance phase when the bacteria will stop multiplying and just produce acid. This is really important because it is this that makes for a pH curve.
Do they stop reproducing because there is not enough sugars left in the milk? Its all been consumed so they stop reproducing and just produce acid, because whatever bacteria is left is consuming whatever sugars are left?
Make sense? The curve is about how active bacteria are at specific temps. The slope of the curve will differ based on strain and temp, and you need to know this to time everything properly.
I think so. So say if I have a particular cheese that has to be at a specific PH at a certain time. Its all about controlling the rate of bacteria so that it hits the correct PH at that particular time. This can be controlled by draining and heating, also the amount of culture added?
You stretched out your pH curve because effectively, heating is like adding 1/50 of the right amount (or some other similar small amount).
So heating is like adding culture? Its speeds up the bacteria growth which in turn consumes more sugars producing more acid?
Like stretching it out so the drop is really slow? That's true, but I wouldn't call it upsetting. Causing swings is upsetting. Like if you added baking soda or lye to the milk to increase pH, that would be upsetting. You just slowed everything down.
So slowing things down don't really upset thing, its only if the PH increases and decreases.. that's upsetting the curve?
For example, in cheddar, you salt at around 5.4. By the morning, the cheese is 5.0-5.1. Recent studies have shown that lactococcus will continue to produce acid and metabolize sugar even after death.
So salting will just slow down the build up of acid, not actually stop it?
Quote from: steve brown on September 08, 2010, 03:39:26 PM
In rennet cheeses, where the k-casein is cleaved and then curd is formed, the acid buildup is important because it removes calcium from the micelle. Meaning you have this complex casein "thing" held together by colloidal calcium "glue", and if that glue is removed by acid, it influences the character of the cheese. A swiss will have most of its calcium in tact, whereas a cheddar will not
So, the acid produced by the bacteria removes calcium which influences the character. So if Swiss cheese has most of its calcium in tact this means that its pressed and salted at a higher PH level that Cheddar which has has less calcium in tact? So is this the reason why some curds are slightly more 'rubbery' and some are more 'sticky' ? Is that the calcium glue you mention or is it simply because there is more or less whey in the curd?
Whey drain pH, more than anything, determines final calcium content. That's because you typically fuse the curds when the calcium is drained, and also remove lactose (food) by removing the whey.
But yes, swiss is both drained at higher pH, and salted at slightly higher pH. Yep, curd rubberyness is all about the calcium, same with stickyness. Although moisture also plays a role. But mostly, it's the calcium.
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That's why you drain the whey from cheddar at a lower pH (6.0-6.1) and also let the acidity build up some more afterward.
Sorry if this is a simple question but why drain the whey? I have read recipes that call for draining but I thought this was done so that the drained whey could be heated and then added back to raise temperatures.. Is this correct? Raising temperature will speed up bacteria growth that will then produce more acids which are needed for Cheddar like you mentioned.. Speeding up the PH curve?
Not many cheeses call for reheating the whey and adding it in. Most drain whey to gather up the curds and let them knit. Whey draining is just natural, you do it to remove the curds. Yes, higher temps will cause faster acidity development.
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Then there's a maintenance phase when the bacteria will stop multiplying and just produce acid. This is really important because it is this that makes for a pH curve.
Do they stop reproducing because there is not enough sugars left in the milk? Its all been consumed so they stop reproducing and just produce acid, because whatever bacteria is left is consuming whatever sugars are left?
It's more complex than that, but that's the gist of it. Too high population density, not enough food, not right pH for growth phase triggers maintenance phase.
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Make sense? The curve is about how active bacteria are at specific temps. The slope of the curve will differ based on strain and temp, and you need to know this to time everything properly.
I think so. So say if I have a particular cheese that has to be at a specific PH at a certain time. Its all about controlling the rate of bacteria so that it hits the correct PH at that particular time. This can be controlled by draining and heating, also the amount of culture added?
yes, but be careful about draining. It's not like you're balancing only pH and time. You're also balancing moisture in the curd (VERY important, I would say one of top 5 challenges for beginners), and other stuff. So you have to make it all fit. Meaning say you added too little culture and moisture in curd and temps are right but pH is wrong. What do you do? Just settle the curd under whey and wait. Or say you raised heat too much, what do you do? Stir less to prevent excess moisture loss in the curd because both heat and agitation cause curd to lose whey, so you take the agitation away. It's all about mastering the tradeoffs.
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You stretched out your pH curve because effectively, heating is like adding 1/50 of the right amount (or some other similar small amount).
So heating is like adding culture? Its speeds up the bacteria growth which in turn consumes more sugars producing more acid?
Well kind of. Remember even with the freshest culture, if that culture is not in a growth phase, there is a lag before it will crank up acid production. So it's more like you add culture in the beginning and then regulate it. You shouldn't add culture after the initial inoculation and rennet addition, you should now manage time, temp, pH, and curd moisture/size.
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Like stretching it out so the drop is really slow? That's true, but I wouldn't call it upsetting. Causing swings is upsetting. Like if you added baking soda or lye to the milk to increase pH, that would be upsetting. You just slowed everything down.
So slowing things down don't really upset thing, its only if the PH increases and decreases.. that's upsetting the curve?
I don't like that phrase at all. It's distracting to me because again, you're trying to work with the natural acidification and pH drop. You can extend the lag phase in the beginning or slow down the rate of acidity development, but that's about it. Let's think about the acidity curve as a buildup of acidity over time, where the derivative may be manipulated by the controls of temp, initial culture amount, pH, food, and time.
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For example, in cheddar, you salt at around 5.4. By the morning, the cheese is 5.0-5.1. Recent studies have shown that lactococcus will continue to produce acid and metabolize sugar even after death.
So salting will just slow down the build up of acid, not actually stop it?
Correct, except not sure if you mean that the pH will continue to decrease to some low number after salting, such as 4.5. It won't. pH will drop a little after salting or brining. But salting doesn't freeze the pH. More correctly, it slows down acidity, and then is one of the helpers to stop it.
Great..
I really do appreciate your patience. My brain is a little frazzled but I have had a breakthrough with something I've never quite got my head around...
Many thanks!
K, I type fast and my brain is usually doing 3 things at once, so please let me know if I'm not clear. I don't take my time to always think through everything I type here, but I try to be concise about the nuances. Think about it in terms of what the bacteria are doing, what the bacteria are doing to the milk, what the rennet is doing to the milk, and how it all fits together. If you get stuck about one or any of those dynamics, let me know, I'll try to explain.
You explain really well. I just have to break things down and actually visualise in my head what's going on. You have covered a huge chunk and the more I understand the more questions I have but I think that's enough for one day :o
Id like to have more of an understanding of what Rennet is actually doing now I have a greater understand of PH curves and bacteria but I'm going to have a dig around the forum before I start asking any questions.
Many thanks Linuxboy and keep up the great work are you doing here...
Enzymes for cheese - CHY-MAX® M coagulant (http://www.youtube.com/watch?v=HyF8DVm-oqA#ws)
Try that. Also I don't want to be self-aggrandizing here, but if you have time read through all my past posts (and Sailor's and Wayne's, and Debi's, and Francois, and and and...). I covered a lot of this before.
I'll second Steve's Thank You and Wow for the great info.
And I'll also second LB's suggestion of reading the archives for all of the forums on this very board. Incredible info, just a pleasure to read and abundantly informative.