How to test scientifically if milk is bad

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In summary, the project is looking into ways to increase the shelf life of milk, and one option is measuring the pH and concentration of volatile organic compounds.
  • #1
chemisthypnos
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I am working on a personal project that I believe can increase the shelf life of milk in a refrigerator. I want to know if anyone knows any scientific ways of testing if milk is bad (due to bacterial growth) as I would prefer to avoid having my family sample a statistically significant sample size of milk samples until they go bad (I won't be trying the potentially bad milk myself to avoid bias...of course!)

I had considered monitoring the milk samples by pH as lactic acid is the cause of the sour taste of bad milk, but an acidity measurement doesn't tell you when the milk is detectably sour to a taster. Perhaps there is a standard?
 
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  • #2
Guessing there are kits or services you can get for money that would be pretty good, since industry regulations would require them.
You would probably want to figure out what you really want tested to save money.
If it only requires a simple test, you might be able to do it your self.

Google a lab near you.
Here's a lab.
Screen Shot 2019-10-31 at 10.40.43 PM.png
 
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  • #3
chemisthypnos said:
I am working on a personal project that I believe can increase the shelf life of milk in a refrigerator. I want to know if anyone knows any scientific ways of testing if milk is bad (due to bacterial growth) as I would prefer to avoid having my family sample a statistically significant sample size of milk samples until they go bad (I won't be trying the potentially bad milk myself to avoid bias...of course!)

I had considered monitoring the milk samples by pH as lactic acid is the cause of the sour taste of bad milk, but an acidity measurement doesn't tell you when the milk is detectably sour to a taster. Perhaps there is a standard?
I think for an initial test that a pH probe would be a good guide. You could compare it with ordinary milk when at its end date.
 
  • #4
I date our milk to the hour, lactose free, when it is opened. This milk has a relatively long expiration date which I am guessing is because the milk is heated or nuked to kill bacteria. I have set a 72 hour use it or lose it rule. At the three day limit my nose can just detect spoiling and my sense of smell is not that great. Your nose and your taste buds may actually be a pretty good detector for milk that is starting to go bad, not scientific though.
 
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  • #7
chemisthypnos said:
I doubt that I will have access to that much complicated machinery for the purposes of this experiment, though.
The complicated gas analysis was only used to verify their colorimetric method. The method itself simply consists of evaporating Schiff reagent onto SiO2 particles and exposing it to vapors given off by milk. The color change indicates the concentration of VOCs (and presumably the spoilage of the milk).

chemisthypnos said:
I think that perhaps the Resazurin test may be adequate. http://www.fao.org/ag/againfo/resources/documents/MPGuide/mpguide2.htm
This will probably also be fine.
 
  • #8
Spinnor said:
I have set a 72 hour use it or lose it rule.

Do you store it then open it at the expiration date to get this behavior? UHT milk should last at least a week after opening if the expiration date is far off. I use UHT half and half and it often takes several weeks to consume and it is still good even though the recommendation is a week.

Do you keep it refrigerated?

BoB
 
  • #9
rbelli1 said:
Do you store it then open it at the expiration date to get this behavior? UHT milk should last at least a week after opening if the expiration date is far off. I use UHT half and half and it often takes several weeks to consume and it is still good even though the recommendation is a week.

Do you keep it refrigerated?

BoB

The expiration date is always about a month or more away, just bought milk last night and it is good till 12/18. It is keep refrigerated though a infrared thermometer shows the fridge is not cold enough. I got really sick from meat that was not properly refrigerated long ago and I don't want any animal protein in the fridge more than 2 or 3 days. We can easily use a half gallon of milk in 3 days and in three days my nose tells me it is starting to get a bit funky.
 
  • #10
Spinnor said:
the fridge is not cold enough.

I would fix this first before trying to find an expensive way to measure milk spoilage. What temperature did you measure?

BoB
 
  • #11
rbelli1 said:
I would fix this first before trying to find an expensive way to measure milk spoilage. What temperature did you measure?

BoB

I have a cheap way to measure milk spoilage, I sniff it.

The fridge was 43 F near the top and 41 F near bottom, turned it down.
 
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  • #12
That is way too high. The FDA recommends below 40. The closest you can get to 32 without freezing anything is best. Good Housekeeping recommends between 35 and 38. Only place freeze tolerant items or things with high sugar, salt, or alcohol content near the cooling outlet vent.

BoB
 
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  • #13
I get a strangely wide variability of spoilage, from 2-3 days, to around 8 at times ( I actually consume it without any problem.) Who knows what lurking variables may be affecting this.
 
  • #14
WWGD said:
from 2-3 days, to around 8 at times

I see that with regular pasteurized milk too. I had a bottle once start to smell strongly of the back end of a cow a day or so after I bought it.

The OP is talking about UHT milk which should last much longer even after opening as long as it is kept properly cold.

Drinking directly from the bottle or leaving it out for long periods during meals could be a cause of accelerated spoilage.

BoB
 
  • #15
rbelli1 said:
pasteurized milk too.
"Pasteurization" is a process taken for granted; maintenance of milking machines is preventative in some dairies and post-failure in others, as is cleaning of pasteurizers; seasons change and temperature regulators fail, particularly in fall and spring, i.e., the milk never gets to sterilization temperature.
 
  • #16
Also note that there are different Pasteurization regimes in the US, higher temperatures increase shelf life:

None - so-called raw milk. This is illegal for commerce in some states and in others highly regulated.
Ex: you can buy raw milk in New Mexico only directly from the producer. Not a retailer or dairy. Raw milk was grandfathered in for the largest grocery cooperative here. So La Montanita Coop sells raw milk. Sometimes. In other words the whole thing is a mess from the getgo. IMO.

145 °F minimum for at least 30 minutes

161 °F minimum for at least 15 seconds

280-302 °F, minimum 280 °F for at least 2 seconds - Ultrapasteurization

Gamma irradiation is not used in the US AFAIK.

Ultra-pasteurization provides the longest refrigerated shelf life, up to 60+ days. It can also degrade dairy flavor agents like lactones. Massive grocery chains (like Walmart, Aldi, etc.) can dictate to dairy suppliers exact Pasteurization specifications to increase shelf life and reduce losses. Those listed above are minimums.

Mom&Pop literature:
https://ofbf.org/2009/03/06/the-facts-about-ultra-pasteurized-milk/
 
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  • #18
chemisthypnos said:
I am working on a personal project that I believe can increase the shelf life of milk in a refrigerator. I want to know if anyone knows any scientific ways of testing if milk is bad (due to bacterial growth) as I would prefer to avoid having my family sample a statistically significant sample size of milk samples until they go bad (I won't be trying the potentially bad milk myself to avoid bias...of course!)

I had considered monitoring the milk samples by pH as lactic acid is the cause of the sour taste of bad milk, but an acidity measurement doesn't tell you when the milk is detectably sour to a taster. Perhaps there is a standard?

I would suggest pH, or optical testing. When milk goes bad one sign is de-homogenization of the emulsion.
 
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  • #19
Wow, there’s an ELISA test for butyric acid! That’s one of the things you taste/smell when milk goes bad.

https://www.mybiosource.com/ba-general-elisa-kits/butyric-acid/2033682
 
  • #20
Very simply, check how long it's been in the refridgerator, look at it, and smell it. Maybe scientific enough.
If it is old (maybe more than a week) then no matter look or smell, it is finished - discard it.
Otherwise, if look and smell is clean, probably (but maybe not to your scientific standard) it will be ok, TODAY.

Do not follow all that if you want to be MORE certain.
 

1. How do I know if milk is bad?

There are a few signs that can indicate milk has gone bad, including a sour or off smell, discoloration, and curdled texture. Additionally, if the milk has been sitting out at room temperature for too long, it is likely spoiled.

2. What is the best way to test if milk is bad?

The most reliable way to test if milk is bad is to smell it. If it has a sour or unpleasant odor, it is likely spoiled. You can also check for any visible signs of spoilage, such as curdled chunks or discoloration.

3. Can I still consume milk if it has passed its expiration date?

It is not recommended to consume milk that has passed its expiration date. The date is set by the manufacturer as a guideline for when the milk is at its freshest and safest to consume. After the expiration date, the milk may have started to spoil and could potentially make you sick.

4. Is it safe to taste milk to see if it is bad?

No, it is not safe to taste milk to determine if it is bad. Spoiled milk can contain harmful bacteria that can cause food poisoning. It is best to rely on other methods, such as smelling and checking for visible signs of spoilage, to determine if milk is bad.

5. How can I prevent milk from spoiling?

Milk should be stored in the refrigerator at a temperature of 40°F or below. It is important to keep the milk container tightly sealed to prevent exposure to air and bacteria. Additionally, make sure to consume the milk before the expiration date and do not leave it sitting out at room temperature for an extended period of time.

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