Author Topic: Pasteurization Temp & Time vs Curd Strength & Protein To Fat Ratio Discussion  (Read 4312 times)

Offline RenaissanceM

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Never having the opportunity to have proper kind of milk for cheesemaking, I was hoping Someone can describe the differences in curd strength between milk that has been pasteurized at a maximum of 72 deg Celsius (for no more than 15 sec) and store bought milk which is usually pasteurized between 78-80 deg Celsius.

I have notice considerable differences between non-acidified rennet only cheese (such as Haloumi) and other acidified cheeses (such as Mozzarella). Flocculation is always faster in the acidified milk when held at the same temperature (when all else being equal). I also noticed the curd is firmer and less prone to shatter with the acidified milk.

Is it possible to use milk pasteurized at 78 deg Celsius and not have shattering or significant shattering of the curd? I realize why the higher pasteurization temp causes the weak curd however I was hoping there may be a way to minimize it (such as extending the rennet time etc.)

I compaired few different brands of milk using rennet only coagulation and found the filtered (and more expensive) milk curd to shatter much more.

I was also wondering if non-homoginized however still pasteurized at 78 deg Celsius will yield a stronger curd?


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Offline Alex

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I pasteurize raw milk for cheeses that I do not intend to age for 60 days and up. The temp I do that is 72-74 deg C, so I don't think a little bit higher is so significant. For this type of milk you have to add CaCl, that will give a better and firmer curd.
Quote
I was also wondering if non-homoginized however still pasteurized at 78 deg Celsius will yield a stronger curd?
Non-homoginized milk will give a better curd. Homogenized milk will make only lactic coagulated type of cheeses.
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Offline Sailor Con Queso

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You can definitely make good cheese with pasteurized homogenized P/H milk, but there are some issues to be aware of.

1- Avoid ultrapasteurized milk for hard cheeses. The milk labels do NOT always say they are UHT. Look for low temperature pasteurized / non-homogenized if available. Worth the trouble to find a good source.
2- You may have to try several brands to find one that works well.
3- You will have to use CaCl2 (Calcium Chloride) to repair calcium damage, improve curd set, and improve yield
4- The curd set is usually not as good as with raw milk
5- Lactic cheeses may actually do better with P/H milk
6- Adding a little nonfat dry (NFD) milk powder can definitely improve protein ratios, improve curd set, and improve yield. I use full fat milk for my Parmesans and Asiagos for example but add NFD milk to improve the protein ratios.

Other issues, but that's a start
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Offline RenaissanceM

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Alex: from what I understand the effect of heat treatment is very sensitive to the time of heating and the exact temperature. Slight variations in heating time result in variation of the properties of the heated milk.

"Mild heat treatments are considered to have no or little effect on the whey proteins of milk, although there are reports that heat pasteurization (72°C for 20 s or 73°C for 15 s) could cause denaturation of approximately 7% of the whey protein fraction of milk (Jelen and Rattray, 1995)."

One of the possible causes of poor curd forming properties of milk treated at a high temperature is the denatured whey protein interacting with the casein and impairing the clotting abilities of the casein by either preventing the rennet clipping of the k-casein thoroughly and/or not allowing the micelles forming a strong bond by taking too much surface area on top of the micelles and hence not allowing them to bond in a tight manner.

Sailor: Unfortunately here in Canada the milk is heavily regulated. Even though government regulations allow pasteurization at 72 deg Celsius for 15 seconds, almost all of the dairy producer (that I have found out so far) choose to do it at 78 deg or higher in order to save time and increase the shelf life. As you may also know selling raw milk is illegal this country (even though you can buy alcohol and drink yourself to death)  :o
I was able to find one smaller dairy producer that sells non-homogenized milk (although past at 78 deg) for a minimum purchase of 20 Litres. I will give that a go and note any difference in curd strength.

I find it very frustrating to start stirring the curd and having it shatter into uneven pieces. I've had good results making Haloumi however I know the consistency in size will make a difference in some of the ago ripened cheeses.

I do use CaCl2 but never used milk powder. What kind do you use? The non-instant or the instant?

Offline Sailor Con Queso

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You may find a big difference using non-homogenized milk. I use instant NFD milk powder. Definitely worth a shot with the higher temperature pasteurization.

There are lots of Canadians making good cheese. You might want to talk with Margaret Morris at Glengarry.
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Offline Susan

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Sailor,
Am I remembering correctly that you generally use raw milk?  If so, you are still adding the instant milk powder?  Or is this only with pastuerized milk.  What is the advantage of using whole milk plus milk powder for paremesan vs using skim as I've often seen?  I'm guessing richer flavor and the powder still helps get the right texture?
Susan

Offline Sailor Con Queso

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I use both, but right now I am using low temp pasteurized, non-homogenized milk from JD Country milk. They are a Mennonite family out of Russelville, KY. I own a design and printing company and am doing marketing for them, so we are trading milk for services. FYI they are the ONLY farm bottled milk in Kentucky. And it's in old fashioned glass bottles. Fabulous milk available at Whole Foods, Good Foods Co-Op, etc. I will be changing over to their raw milk as soon as I have a delivery plan approved by my inspector. I am using the Mennonite connection as a part of my own marketing.

Parmesans and other Italian types generally call for lower fat milk. That influences texture and flavor and is a part of what makes them a really hard grating cheese. The lower fat content also greatly reduces the yield. So what I do is start with the full fat (3.5 - 4%) fresh farm milk. I add one cup of the NFD powder for every 5 gallons of milk. This drastically improves the protein to fat ratio and I do not lose much if any yield. As an example, I make 35 gallon batches and normally end up with 6 wheels of around 5.25 pounds each. If I were to use 2% milk, I would end up with just 5 wheels for the same amount of effort. The NFD brings the yield back to 6 wheels.
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Offline Susan

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And is then the taste and texture similar to a parmesan made with 2% milk?
Susan

Offline linuxboy

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Susan, when making cheese, one very, very, highly important factor is the ratio of protein to fat in the milk. This is because based on the number of fat molecules when compares to protein molecules, the curd structure will be way different. It will have different properties in terms of:

- The size of the openings in the curd matrix. More protein tends to lead to smaller openings because protein molecules are smaller and you get a tighter bond in the matrix.
- The distribution of fat molecules. This also has to do with homogenization, but if you have more fat molecules, they are physically bigger. And with bigger fat molecules, even though the spaces in the matrix are bigger, anything that travels in or out has a longer route to travel. So for example, the whey drains much slower.
- The strength of the curd. This is somewhat self-explanatory. But curd (the gel/matrix) is formed by proteins that are bonded to each other. If there are more proteins, the bonds are stronger. Think of curd like a chainlink fence. That fence is made up of a bunch of casein micelles that are bonded to each other. And then think of the fats like snowballs that you throw at the fence and they stick. And then expand that fence in three dimensions, and that's basically what curd is.

I'm talking about rennet cheeses for all this, enzyme-coagulated.

Commercially, milk is standardized to reduce the variability. There are optimum targets for the protein to fat ratio. This is because most cheese processes are the same... you use a certain starter amount 1%, usually, sometimes more. You use a heat schedule and curd size and floc/set time to get to a specific gel strength and moisture target before knitting curds and pressing them. And you get the time, acidity, and moisture level to coincide for the specific type of cheese you make.

For parm, the moisture target is really low, something like 22-25%. You can't use a full-fat milk for that because in a full-fat milk, the PF ratio is something like .6-.8. That would give you a curd that releases whey slowly, that leeches fat from the curd because the matrix would be weak, and where the final moisture and solids/fat targets would be all wrong. So one way to remedy this is to skim the fat or centrifuge it off in a separator. Or, add back protein to get the PF ratio to be correct. The proper PF ratio for parm is something like 1.25... which is usually 2.2-2.6% fat for normal holstein/holstein-cross milk. But if you add back protein, you can use much higher fat milk, and keep the rest of your make the same. Texture, flavor, maturation, curd behavior, etc will be the same.

+1 Sailor, great ideas on practical PF modification at home. It's very easy to adjust SNF with powder.
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Offline linuxboy

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Quote
"Mild heat treatments are considered to have no or little effect on the whey proteins of milk, although there are reports that heat pasteurization (72°C for 20 s or 73°C for 15 s) could cause denaturation of approximately 7% of the whey protein fraction of milk (Jelen and Rattray, 1995)."

Very ambiguous statement, potentially wrong based on how interpreted. Standard 30 min at 63C lower  temp pasteurization will denature more whey proteins than fast 72C-73C. The first one denatures something like 8% and the second more like 4%. Where it goes bad for cheesemaking is twofold

1) Using higher temp or longer time than required by law to make up for poor milk quality by essentially "boiling" the milk. This causes whey protein adsorption
2) Homogenization that causes the fat to be broken up and the pressure will actually cause the fat to be adsorbed by the casein micelles. Also highly damaging to cheesemaking, causes curd shattering if the pressures are too high.

My suggestion is to try all the milks available and use the best one. It took me months to figure out a consistent, cheap commercial milk. For anyone here in the PNW reading this, that milk is the one from Sunshine Dairy out of Portland. They pack white label milks in the white plastic gallon containers for Whole Foods and Trader Joes in this area.
« Last Edit: October 18, 2010, 03:15:07 PM by linuxboy »
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Offline RenaissanceM

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Thanks for the info guys. I pretty much tried all the major three brands which are sold under 6 various names and the best (which is still not great) is a 78 deg Celsius (unknown how many seconds as they don't want to reveal it). The only one I haven't tried yet is from a smaller dairy pasteurized at 78 deg Celsius (174 F) and it's non-homogenized. I will give that a go.

I have two follow-up questions:
1) what is the highest pasteurization temp/time that you can use and still produce decent curd/cheese?
2) For the "proper" milks for cheesemaking, if you use rennet only (as per manuf. specs) to set a curd that's around a ph 6.7 and follow a floc multi of 3-3.5, how much curd breaking or shattering is reasonable to have (if any)?

Offline linuxboy

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#1, hard to tell. Maybe 10%. Whey protein denaturation is just one of the factors. And you can make up for it some by adding CaCl2.

#2 I would add rennet at 6.5-6.6. Makes for a better set to have more acidity. I standardize most of the time and add at 6.5 (for cow milk). But with proper milk, curd should not shatter at all regardless of pH. pH just affects the rate at which rennet acts.

Here's a chart that may help from the book Continuous thermal processing of foods.
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Offline RenaissanceM

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Great, thanks for the info linuxboy. That's a great graph too. I guess I will know that I have a suitable milk when I see it.

I didn't quite understand your answer to question #1 though. Did the 10% refer to the curve in the graph?

Offline linuxboy

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Yes, 10% of whey proteins denatured. The more they are denatured, the more that can be adsorbed, and the worse the gel strength.
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Offline Sailor Con Queso

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All milks even under the same brand are not the same. In our area, one of the major producers is Dean Foods. They use exactly the same milk for both Sam's Club and Kroger's (a grocery chain) with private labeling. However, Kroger's policy requires a longer pasteurization for their milk. Why? It's simple. Milk that is heated higher and/or longer has a greater shelf life. Sam's Club turns milk over so rapidly that shelf life isn't an issue, so they let Dean Foods pasteurize "normally". Dean in turn reduces pasteurization time substantially. Why? Again it's simple - lower energy costs for production.

So Kroger's milk is worthless for cheese, while Sam's Club milk actually works pretty well. That may not be the case in other parts of the country.

Susan - yes I have been very happy with the results using NFD to increase protein. My farm fresh milk is so rich that I use NFD at half the dosage on non-Italian types as well. I always use some in Mozzarella and even yogurt. Always improves curd set and yield.  I never use it on Blues or other higher fat cheeses. As LB said, the P/F (protein to fat) ratio is really important. That is something that most amateurs don't pay enough attention to. Perhaps LB can give us a formula for figuring out the P/F ratio when adding NFD powder. Hint, hint. Oh no it's a segue. ::)
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