Hydro Flasks are great at keeping water cold for 24+ hours but can you put milk in a Hydro Flask and how long is it safe to keep milk in a Hydro Flask before it goes bad?
It's a good question because no one wants to drink warm milk, plus the fact that bacteria can quickly grow in warm milk that can lead to vomiting, diarrhea and even food poisoning.
So can you put milk in a Hydro Flask and if so how long will it keep?
You can put milk in a Hydro Flask and it will last 2-6 hours without spoiling depending on the starting temperature of the milk and the outside temperature. You can keep milk for 24 hours in a Hydro Flask with a reusable ice pack like the myColdCup ice stick (or similar).
But before you go out there and pour milk in your Hydro Flask and head out for the day there are some important things you should know to ensure your milk stays safe to drink all day long.
Safely Keeping Milk in a Hydro Flask
Milk contains the bacteria lactobacilli and while the pasteurization kills most of it it can quickly grow back given the right conditions.
Milk in kept in your fridge at 40ºF (4ºC) which helps to stop the bacteria growing rapidly.
However, once the temperature is between 40-140ºF (4-60ºC) this is considered by the USDA to be the “danger zone” for bacteria growth.
Milk being kept in the danger zone temperature range should be consumed within 1-2 hours or discarded.
The key to safely keeping milk in a Hydro Flask is to keep it below 40ºF (4ºC) for as long as physically possible.
Theoretically if you can keep your milk below this temperature then you can hold milk in a Hydro Flask for 24+ hours. However, keeping milk below this temperature isn't easy.
Ideally, Don't Put The Milk Straight From The Fridge
Milk in your fridge will be right at that 40ºF (4ºC) temperature so once you put it in your Hydro Flask it won't stay that cold for long.
It'll quickly enter the danger zone temperature range and you'll have maybe 2-4 hours in order to drink it before you start risking it going bad.
Start Your Milk At a Colder Temperature, Around 2ºC
Instead of getting milk out of the fridge door you'll want to make your milk a bit colder. Basically as close to freezing temperature as possible without it actually freezing.
This can be a bit tricky to achieve.
Sometimes you can do this by placing your milk right at the back of the fridge near the cooling fan vent. Other times you might want to place it in the freezer for a bit before putting it in your Hydro Flask.
You'll also want to cool down the inside metal of your Hydro Flask with some ice or cold water before putting your milk in.
Put iced water in the Hydro Flask for 10 or so minutes and then discard before putting your milk in.
It won't make a huge difference but it'll ensure that the warm metal walls of your Hydro Flask don't warm up your milk.
Use A Reusable Ice Brick
By far the best way to keep milk for a long time in a Hydro Flask is to use a reusable ice brick, ideally one specifically designed for water bottles like these affordable myColdCup ice bricks you can get at Amazon.
You can use regular ice but it isn't ideal because as it melts it will dilute your milk.
The reusable ice bricks stay contained in plastic as they melt so they won't dilute your milk. You can also reuse them over and over again.
Using an ice brick or two you should be able to keep milk for hours in a Hydro Flask. 6-24 hours depending on how much ice you use and how hot the day is.
Use UHT/Long Life Milk Instead
If you don't mind the taste then using UHT (ultra high temperature) or long life milk is a better alternative.
It has been treated at a much higher temperature which is much more effective at killing bacteria.
These milks can last months without going off so putting them in a Hydro Flask for a couple of hours should be fine.
You still want to do your best to keep the milk out of the danger zone temperature otherwise bacteria can grow, but the risk is a lot lower than regular milk.
Can You Put Hot Milk in a Hydro Flask?
When it comes to keeping hot milk in a Hydro Flask you still have to be aware of the danger zone temperatures where bacteria can easily grow.
Temperatures under 140ºF (60ºC) are perfect breeding grounds for bacteria and they will cause your milk to spoil rather quickly, usually within an hour or maybe 2.
However, if you can keep the temperature of the milk above 140ºF (60ºC) then you can keep the milk in your Hydro Flask for extended periods of time.
To do this first heat up the inside of your Hydro Flask by filling it up with boiling water and leave the water to sit for 2-5 minutes in the Hydro Flask.
Then heat up your milk to near boiling temperature and pour it straight into your Hydro Flask (after discarding the boiling water of course).
Close the lid quickly and don't open it until you are ready to drink it.
This will keep the milk safe to drink for around 6-8 hours or maybe even longer.
However, keeping milk at a high temperature like this for a long period of time and denature the proteins in the milk and maybe cause the consistency and taste of the milk to change.