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Over the years I have noticed that when I buy milk in glass bottles it will stay fresh-tasting longer than milk bought in plastic jugs or paperboard cartons. This includes other milk products such as whipping cream and half & half.

What I don't know is why this happens. Most US grocery stores sell these products in plastic or paperboard containers, with dairies being the place to get them in glass bottles.

I have researched quite a bit and found some very interesting information, but most of it is in regard to nutrition or environmental, production, and transortation information.

Does anyone know why milk products stay fresh longer in glass?

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    The first thing that comes to mind is that glass stays cold longer than in plastic jugs and cartons. When the cold chain is broken for a short time (e.g. when packing the milk into the shelves or the time between picking the milk from the fridge in the store and putting it into the own fridge) the milk in the glass doesn't warm up as much as in other packages.
    – Ching Chong
    Jun 28, 2015 at 15:21
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    Have you had a look at this article yet? While it doesn't go into much detail on what "tastes fresher", it does mention that light-proof containers prevents degrading of, among other things, the vitamins in the milk.
    – eirikdaude
    Jun 28, 2015 at 16:03
  • @eirikdaude Thanks. I did read it when I was looking for an answer to my question. It is excellent information and an interesting read about the pros and cons of each type of container, but unfortunately does not give me an answer.
    – Cindy
    Jun 28, 2015 at 16:07
  • Yeah, I've looked a bit further into it, and it seems there isn't very much info on it beyond it being noted that you'll want a non-transparent container, and you want a type of container which has an airtight seaaling mechanism. There have been a couple of references in a couple of the papers I've liked which has looked promising, but unfortunately I haven't had access to the source material. Interesting question at any rate, upvoted :)
    – eirikdaude
    Jun 28, 2015 at 17:31
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    I would think that, over time, the plastic would leech some flavors or allow in some outside air (plastic bottles aren't completely non-porous)... glass is less porous.
    – Catija ♦
    Jun 29, 2015 at 0:54

3 Answers 3

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First off I want to point out the term "fresh". While some containers might keep milk from spoiling for longer, it may not taste as nice.

Several things might be why:

1.) Plastics leach flavor and odor into the milk. Cardboard cartons are also lined with plastic, not wax since about the 1940s. I would say this is likely the biggest impact-- I've always found plastic containers make drinks and food taste downright funky.

Plastic milk jugs are made of high-density polyethylene. The FDA considers this material safe, but just because something is safe doesn't mean it doesn't impart a flavor.

Study from Journal of Dairy Science showing glass having least effect on taste:

"...overall, the development of water off-taste occurred least in glass containers and most often in high density polyethylene containers..."

2.) Glass bottles feel colder. Ice cold milk tastes better(fresher) to most people.

The thing is, it's not actually colder while in the fridge. Glass has a higher thermal conductivity than most plastics. That means heat can transfer through it faster than plastic. The second law of thermodynamics demands equilibrium, so while your hand makes the milk hotter, the glass of milk makes your hand colder. Because of glass's higher thermal conductivity, it does this faster than plastic and we sense the glass as being colder.

So while it's not -actually- colder and wouldn't keep the milk from spoiling for longer, it would affect our perception of how cold it is and therefore also the taste.

Packaging of milk varies so a thicker glass bottle might also keep the milk colder while it's sitting on the counter vs most thin plastic milk jugs. There are a lot of variables with packaging so it really depends on what you're comparing.

3.) Oxygen Permeability: Glass has no O2 permeability whereas most plastics do.

Starting in 1937 the Methylene Blue Dye Reduction Test used to be one of the main statutory tests for checking if milk was bad by checking how much oxygen is present in the milk. This lets you know how much aerobic bacteria is in the milk (bacteria that requires oxygen). This is actually a science experiment you can do yourself. While we do have newer, better tests for handling milk in bulk refrigeration these days, it's important to note for a long time this was a large part of measuring milk quality.

4.) It just takes time to process, test, and ship milk. You mentioned it yourself-- usually to get a glass bottle you have to get it from a dairy, something local and closer to home. So it hasn't traveled as far.

Also, while it's not legal everywhere, some people will sell raw milk in glass bottles so there isn't even time wasted processing or testing the milk. However, raw milk goes bad faster. Still, some people might prefer the taste while it's still good. Processing is done to kill bad bacteria(so it's not a bad thing), but it does take time that eats into shelf life. Milk delivered to you may only be a few hours old. The processing itself can effect the flavor of the milk. Processing plants can hold milk for up to 3 days.

5.) In many areas, the companies that bottle with glass are the ones that are making higher quality milk in the first place. Glass is expensive, and usually only people who are willing to pay more for higher quality milk are going to be the same ones who pay for a higher quality bottle. Glass bottles are good for the environment and so some people are willing to pay more for that. Refillable glass uses about half as much energy vs plastic counterpart. Note here that glass doesn't automatically mean "better milk".

6.) The way food looks affects our perception of taste.

In a 1980 study, subjects were blindfolded and asked to tell whether the beverage they were drinking was flavored orange. Only one in five could. But when they were allowed to see what they were drinking, each of them identified the orange flavor. And when a lime-flavored drink was colored orange, nearly half of respondents thought it was flavored orange

You also see this with high-end restaurants-- they put a lot of value in how the food is plated, going as far as using a ruler to get a perfectly straight line, and wiping up small drips to make the food look perfect. Our vision influences our taste.

Since most glass is translucent and most plastic containers are not, there's a good chance this influences taste as well.

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    We try to avoid too much in the scope of #5 on here (although I admit, I've brought up environmental issues myself) ... but it's possible that the local dairies could be using different pasteurization techniques (eg, longer time but lower temp)
    – Joe
    Jul 2, 2015 at 21:43
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    I suppose my point was primarily that sustainable/organic farmers -usually- have to hold higher standards and animals that are well taken care of tend to produce better tasting products. Companies that care or cater to people who care are more likely to use the environmentally friendly glass products (as that would be in line with the wants of those consumers). Grass-fed, no hormone, and no antibiotics cows will produce milk that tastes different. It tastes better to many people. Glass-bottled milk is more likely to come from companies with cows like that, though certainly not always.
    – Jemmeh
    Jul 2, 2015 at 22:06
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    Can you back up your claim #1 & 2? I searched a bit before putting up the bounty, and my impression was that the amount of chemicals released from plastic coatings of containers is negligible, as is the amount of oxygen getting through the containers (of more import was the cap / seal on the containers, but I digress). There seems to be a few articles indicating that to prevent spoilage, paper cartons are better, but I haven't managed to track down sources for this information.
    – eirikdaude
    Jul 6, 2015 at 11:37
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    While the amount of chemicals leached into milk from plastic containers is considered safe(though some people debate it, government says it's OK), you can still taste it. As with many things on Seasoned Advice regarding taste that's just something from experience-- my own and hearing many others complain about the same thing. I too would think paper cartons keep it not-spoiled longer, but because they are coated with plastic inside it still suffers from the same problem of that plastic taste, which I think is the main reason it tastes "less fresh". Still, I will try to find some more info.
    – Jemmeh
    Jul 7, 2015 at 13:26
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    Regarding #4 - glass bottles don't "get colder," and your link doesn't claim that. They feel colder because they transfer heat quicker when you touch them, and they might stay colder a little longer when milk is removed from the fridge, due to higher heat capacity. But at equilibrium in the fridge, a glass bottle will be the same temperature as other materials.
    – Athanasius
    Jul 7, 2015 at 13:57
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I suspect that it's the source of the milk rather than the container. The shorter the supply chain from cow to your refrigerator, the longer the milk will last in your refrigerator. Mass-produced supermarket milk, which is generally (always?) sold in low-cost plastic containers, spends more time being shipped and distributed than locally-sourced organic milk, which is more often sold in glass containers. So, plastic/glass versus length of shelf life is correlated, but there isn't causation.

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  • "effect of slow cooling after pasteurization on the bacterial flora of milk" The container can change the process. If the glass bottle eliminates one extra movement of product -reducing exposure to O2 perhaps- that could make a difference, no?
    – Pat Sommer
    Jul 3, 2015 at 18:50
  • After pasteurization, the milk is typically cooled quickly in a heat exchanger before it's put into containers.
    – mrog
    Mar 23, 2018 at 18:52
  • Hi, @mrog. I'm not sure what the point of your comment is; would you explain?
    – Daniel Griscom
    Mar 23, 2018 at 22:28
  • @DanielGriscom It was meant to be a reply to Pat's comment. Pat suggested that the container's properties could affect the cooling rate after pasteurization. But the milk is cooled before it enters the containers.
    – mrog
    Mar 23, 2018 at 23:44
  • Ah; I understand. (Then again, Pat's comment was a bit confusing as well...)
    – Daniel Griscom
    Mar 24, 2018 at 0:51
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Glass is truly neutral. Plastics is not. Glass is non-porous, plastic is porous. Glass doesn't leach, plastic leaches. Glass containers are thicker than plastic containers, so stay colder by being a heavier heat sink (it stays colder longer because it takes more heat to warn that column of glass than it does to warm a paper thing plastic jug.

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