How to test scientifically if milk is bad

Main Question or Discussion Point

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?
 

Answers and Replies

BillTre
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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
 
tech99
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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?
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.
 
Spinnor
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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.
 
TeethWhitener
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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).

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.
 
rbelli1
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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
 
Spinnor
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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.
 
rbelli1
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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
 
Spinnor
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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.
 
rbelli1
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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
 
WWGD
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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.
 
rbelli1
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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
 
Bystander
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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.
 
jim mcnamara
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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/
 
Last edited:
chemisttree
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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?
I would suggest pH, or optical testing. When milk goes bad one sign is de-homogenization of the emulsion.
 
symbolipoint
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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.
 

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