How long can milk be left out before it goes bad?
Milk is a staple in most households. It’s commonly used for drinking, cereal, coffee, baking, and cooking. While milk contains nutrients that are beneficial to your health, it can also spoil and cause foodborne illness if not handled properly. So how long can milk sit out before it goes bad?
Introduction
The answer depends on several factors, including the type of milk, its expiration date, whether the container has been opened, and how it was stored. In general, all types of milk including whole milk, 2% milk, 1% milk, and skim milk should be refrigerated at 40°F or below to prevent bacterial growth. The cooler the storage temperature, the longer the milk will stay fresh. Storing milk on the counter or anywhere at room temperature allows bacteria to multiply rapidly.
Types of Milk and Their Shelf Lives
The different categories and varieties of milk have slightly different shelf lives. Here is an overview of how long each type of milk can be left out before spoiling:
| Type of Milk | Refrigerated Shelf Life | Shelf Life After Opening |
|---|---|---|
| Whole milk | 5-7 days past ‘sell by’ date | 5-7 days |
| 2% reduced fat milk | 7 days past ‘sell by’ date | 5-7 days |
| 1% low-fat milk | 7-10 days past ‘sell by’ date | 7 days |
| Skim milk | 7-10 days past ‘sell by’ date | 7 days |
| Lactose-free milk | 7-10 days past ‘sell by’ date | 7 days |
| Evaporated milk | 7-10 days past ‘sell by’ date | 3-5 days |
| Sweetened condensed milk | Unopened – 2-3 weeks past ‘sell by’ date Opened – 3-5 days |
5-7 days |
| Powdered milk | 6 months – 1 year past ‘sell by’ date | 3-5 days |
| UHT shelf-stable milk | Unopened – Until ‘sell by’ date Opened – 7-10 days |
7-10 days |
As shown, unopened shelf-stable UHT milk can be left out at room temperature until its expiration date. Once opened it lasts about a week. On the other end of the spectrum, powdered milk lasts 6 months to a year past its ‘sell by’ date when properly stored.
Refrigeration Temperature
The temperature your refrigerator is set to also plays a key role in milk’s shelf life. Here’s how long milk lasts when stored at different fridge temperatures:
| Refrigerator Temperature | Milk Shelf Life |
|---|---|
| 37°F (3°C) | 10-14 days |
| 40°F (4°C) | 7-10 days |
| 45°F (7°C) | 5-7 days |
A temperature of 40°F or below is recommended. The warmer your fridge, the faster milk will spoil.
Signs Milk Has Gone Bad
Pay attention to changes in the color, smell, and texture of your milk. Here are some common signs that indicate it has spoiled and should be discarded:
- Sour odor
- Clumpy texture
- Yellowish tint instead of white
- Yogurt-like consistency
- Mold around lid or bottom
- ‘Fizzing’ when shaken
Tasting milk to check if it’s gone bad is not recommended. Some bacterial contamination cannot be detected by smell or visual cues alone.
Duration Milk Can Be Left Out by Type
Here is a summary of how long the main kinds of milk can sit at room temperature before bacteria multiply to unsafe levels:
| Type of Milk | Room Temperature Duration |
|---|---|
| Pasteurized cow’s milk | 2 hours |
| Ultra-pasteurized milk | 3-4 hours |
| Powdered milk | 2-3 hours after reconstituting |
| Evaporated milk | 6-8 hours |
| Sweetened condensed milk | 8-12 hours |
| Soy milk | 4-6 hours |
| Almond milk | 4-6 hours |
| Coconut milk (from carton) | 2-3 hours |
| Goat milk | 2 hours |
As you can see, regular pasteurized milk and goat milk are only good for 2 hours max at room temp. Ultra-pasteurized varieties last a bit longer. Store-bought nut milks made from almonds and coconut also have a short shelf life out on the counter. Sweetened condensed milk lasts longest since the added sugar helps prevent bacterial growth.
Does Smelling Milk Allow You to Tell if It’s Bad?
Giving milk a sniff test is not a reliable method to determine if it has spoiled. Milk may give off a sour odor as soon as a few hours after being left out. However, it can still look perfectly normal. Conversely, milk can take on a yellowish tint and smell completely normal at first. So judging by appearance or smell alone is not foolproof.
Bacteria and foodborne pathogens that are dangerous or cause illness may not significantly alter the odor or consistency of milk. To be safe, if milk has been left out too long at room temperature, it’s best to err on the side of caution and discard it.
Does Sour Milk Curdle and Separate When Heated?
Yes, spoiled milk will curdle and separate when heated. Here’s the science behind why this happens:
Fresh milk is a colloid – a stable mixture of fat micelles suspended in solution. The casein proteins and fat in milk maintain this emulsion. However, as milk ages and sours, the pH becomes more acidic due to bacteria metabolizing the lactose into lactic acid. The change in acidity causes the milk proteins to lose their structure and clump together. Bringing the curdled milk to a boil speeds up this curdling reaction. The result is chunks of milk solids separating from the liquid whey.
Can Curdled Milk Still Be Consumed?
Most nutrition experts advise against consuming curdled milk if it smells or tastes bad. The change in texture indicates spoilage occurred. Drinking sour milk unlikely to make you seriously ill. But it can lead to minor symptoms like:
- Nausea
- Vomiting
- Diarrhea
- Stomach cramps
The risks outweigh any potential benefits of drinking spoiled dairy. However, if milk merely curdles upon cooking but still smells and tastes normal, it should be safe to consume.
Why Does Milk Curdle in Coffee and Tea?
Fresh milk can also curdle and separate after being mixed into hot coffee or tea. This happens because milk proteins coagulate when they come into contact with acids. Coffee’s natural acids can cause curdling. The same goes for the tannic acid in tea.
To prevent this reaction, the milk should be heated before adding it to the coffee or tea. The higher temperature denatures the proteins so they are less sensitive to the acids. Gently pouring the milk into the cup after the drink is already prepared will also minimize curdling.
Does Spoiled Milk Come Out in Chunks or Flakes?
Chunky flakes or clumps in your milk is a sure sign it has gone off. This occurs because the milk proteins and fat destabilize and coagulate as the pH lowers. Since refrigeration only slows microbial growth, over time the milk becomes more acidic. The increase in acid causes particles to form throughout the liquid. These clumps may be white, yellow, or greenish in color.
Can Milk Be Donated If Out Too Long?
Milk that has sat out too long should not be donated or repurposed. Dairy banks and other charitable organizations do not accept milk that may pose health risks. Room temperature milk should only kept up to 4 hours maximum, according to food safety guidelines. If milk is left out longer than that, it has entered the ‘danger zone’ of 40-140°F when bacteria rapidly multiply.
Tips for Storing Milk Correctly
To get the longest shelf life out of milk after purchase, follow these storage recommendations:
- Immediately refrigerate milk at 40°F or below after use.
- Keep milk on an interior fridge shelf, not the door.
- Store milk away from strong odors and light exposure.
- Keep storage areas and containers clean.
- Keep different milk types separate to avoid cross-contamination.
- Check expiration dates and use oldest milk first.
- Don’t return unused milk to the original container.
- Close containers tightly after pouring.
- Avoid temperature fluctuations during storage.
Following proper refrigeration guidelines helps slow bacteria growth so milk lasts as long as possible.
Does Milk Go Bad Faster in the Summer?
Yes, milk tends to spoil faster in summer than during cooler months. There are two main reasons behind this:
- Higher temperatures promote faster bacterial and fungal growth.
- Warm weather leads to more opening and closing of the fridge allowing the interior temperature to fluctuate.
To help milk stay fresher for longer in summer:
- Turn the fridge temp down to 36-38°F.
- Only open the fridge when necessary.
- Store milk towards the back where temps are most stable.
- Buy small containers and single servings when possible.
Being extra diligent about promptly returning milk to the fridge in summer heat also helps prolong its shelf life after opening.
Does Ultra-Pasteurized Milk Last Longer Than Regular Milk?
Yes, ultra-pasteurized milk typically lasts longer than conventionally pasteurized milk. Here’s an overview of the key differences:
Regular pasteurized milk:
- Heated at 161°F for 15-20 seconds.
- Shelf life of 2-3 weeks from the pasteurization date.
- Must be refrigerated.
- Lasts 5-7 days after opening when refrigerated.
Ultra-pasteurized milk:
- Heated at 280°F for 2 seconds.
- Shelf life of 60-90 days from the pasteurization date.
- Can be shelf-stable until opened.
- Lasts 3-4 weeks refrigerated after opening.
The ultra-high temperature milk is heated to kills more microbes. This eliminates more enzymes and extends the shelf life. So ultra-pasteurized milk lasts about 3 times longer than regular milk from date of pasteurization.
Conclusion
All milk has a limited timeframe during which it stays fresh and palatable. The length of this shelf life depends on the type of milk, storage temperature, packaging, and handling conditions. As a general guideline, milk should not be left out on the counter for more than 2 hours at room temperature. Pasteurized milk lasts around a week past the printed sell-by or use-by date when properly refrigerated. Ultra-pasteurized varieties can go unopened for up to 3 months. But once opened, all milk should be consumed within 7-10 days for best quality.
Be aware of visible and olfactory signs milk has spoiled. Clumps, color changes, and sour odors indicate it’s time to discard it. Following the recommended storage guidelines helps prevent milk from going bad prematurely. With proper refrigerated conditions, milk can retain its nutrients, creaminess, and flavor for maximum enjoyment within your morning coffee, cereal, or favorite recipes.