Butter looks as though it can sit in a fridge for weeks. But because the change in its flavour happens slowly, it generally goes unnoticed.
What is the composition of butter?
Butter consists of three components.
Milk fat at 80 to 82 percent.
Water at 16 to 18 percent.
Milk solids at 1 to 2 percent.
Those three form an emulsion; the water is dispersed as small droplets within the fat.
Milk fat contains hundreds of triglycerides with different melting points.
Some of those triglycerides carry unsaturated fatty acids.
Unsaturated bonds are the points that react with oxygen; that chemical structure is the basic reason butter deteriorates.
How does butter deteriorate?
Three mechanisms work.
The first is oxidation. Unsaturated fatty acids react with oxygen.
The result is a rancid, waxy taste.
That is the most widespread form of deterioration.
The second is lipolysis. Lipase enzymes in the milk fat break down triglycerides and free fatty acids get released.
Butyric acid forms, giving a sharp, sour smell.
The third is absorbing odours. Milk fat takes up volatile compounds from around it.
Smells of onion, cheese and fish in a fridge pass into butter, and that is an irreversible loss.
| Storage | Temperature | Time | Quality |
|---|---|---|---|
| Fridge, in its wrapper | 4 °C | 2-3 weeks | Good |
| Fridge, in a closed dish | 4 °C | 1-2 months | Very good |
| Room temperature, butter dish | 18-20 °C | 5-7 days | Moderate |
| Freezer, unsalted | −18 °C | 6-9 months | Good |
| Freezer, salted | −18 °C | 9-12 months | Good |
| Clarified, room temperature | 20 °C | 2-3 months | Good |
Why do light and oxygen matter so much?
Both accelerate oxidation.
Light, particularly ultraviolet, excites the fat molecules.
The reaction speeds up.
Butter therefore gets sold in packaging that blocks light.
Foil-lined paper is the most widespread; it provides a barrier against both light and oxygen.
Butter stored in clear plastic containers deteriorates faster.
Contact with oxygen should be reduced too; butter should sit in an airtight container.
A yellowing layer at the surface means oxidation has begun; that layer can be cut away and discarded, but the part beneath follows the same road before long.
How is butter stored in a fridge?
The door shelf is the most widespread place but not the most suitable.
The door temperature fluctuates between eight and twelve degrees.
That is high for butter.
A middle or lower shelf suits better, at four degrees.
The product should not stay in its wrapper; an opened wrapper passes air.
It should move into a covered butter dish or an airtight container.
Glass or ceramic is preferred; plastic holds odours over time.
It should be kept away from strongly scented foods; it should not sit on the same shelf as onions, garlic and ripe cheeses, since odours transfer rapidly.
Can it be left at room temperature?
That is a contested question.
Butter stays spreadable at room temperature, which is a practical advantage.
But deterioration accelerates too.
Salted butter can last five to seven days at room temperature; salt limits microbial growth.
Unsalted butter loses flavour within two or three days.
A covered butter dish is needed.
Water-sealed butter dishes are one solution; the container sits in water and cuts contact with air.
But that method works only in cool kitchens; above twenty-five degrees butter softens and loses its shape.
Can butter be frozen?
It can, and butter is among the dairy products best suited to freezing.
Because its water content is low the ice crystals that form are small.
The emulsion structure is largely preserved.
The change in texture after thawing is minimal.
Unsalted butter keeps six to nine months.
Salted butter keeps nine to twelve; the salt provides additional protection.
Those times depend on the integrity of the packaging.
Freezer burn is the commonest problem; white, dry patches form at the surface and those areas have lost their flavour.
How is butter frozen?
The method directly determines the result.
Butter can stay in its original wrapper.
But an additional layer is needed.
The wrapped product goes into cling film and then into a freezer bag.
Two layers prevent freezer burn.
Portioning is better still; the butter gets divided into pieces of 50 to 100 grams.
Each piece gets wrapped separately.
That allows taking only what is needed and the rest never thaws; that is the most important step in preserving quality.
How is it thawed?
Thawing happens in a fridge.
A hundred-gram piece thaws in eight to twelve hours.
Thawing at room temperature is faster but condensation forms at the surface.
That water creates an environment for microbial growth.
Thawing in a microwave suits only where it will be used immediately.
The product heats unevenly; some areas melt while others stay frozen.
No thawing is needed where it will be used in cooking; frozen butter can go straight into a pan or be grated into a dough.
Thawed butter should not be refrozen; the emulsion suffers a little more with every cycle and the product begins releasing water.
What advantage does clarified butter provide?
Clarifying separates the water and milk solids from butter.
Almost pure milk fat remains.
That produces two consequences.
The first is shelf life; with no water and no protein, microbial growth has stopped.
It keeps two or three months at room temperature.
The second is the smoke point; with no milk solids to burn, the fat can pass two hundred degrees.
It becomes suitable for frying and high-heat cooking.
The disadvantage is losing part of the characteristic aroma of butter; because the milk solids are the source of that aroma, clarified fat stays more neutral and the difference registers in some desserts.
