The layer of oil gathering at the top of the jar leaves most people with the impression that the product has spoiled. Yet that is tahini's most natural behaviour.
Why does it separate?
Tahini is obtained by grinding roasted sesame.
Nothing else goes in.
Sesame contains oil at around 50 to 55 percent of its weight.
That oil leaves the cells during grinding and mixes with the solid particles.
But that mixture is not an emulsion.
There is no bond between the oil and the solids; they merely sit together physically.
The oil is less dense than the solid particles.
Over time the oil rises and the solids settle.
That is a natural consequence of gravity.
Cream rising in milk and natural fruit juice settling work by the same mechanism.
Is separation a sign of spoilage?
No; quite the opposite.
A tahini that does not separate either contains an emulsifier or has had hydrogenated fat added.
Both mean additives.
An emulsifier holds oil and solids together and prevents separation.
Hydrogenated fat is solid at room temperature; it reduces flow and slows settling.
It also carries a risk of trans fats.
The label should therefore be read: good tahini has one ingredient, sesame.
Some products contain salt too, which is an acceptable addition.
Products containing sugar, vegetable oil, emulsifiers or preservatives belong in a different category.
| Product property | Meaning | Assessment |
|---|---|---|
| Clear oil separation | No emulsifier | Positive |
| No separation at all | Emulsifier or hydrogenated fat | Check the label |
| One ingredient: sesame | No additives | Best |
| Sesame plus salt | Acceptable | Good |
| Vegetable oil added | Diluted | Low quality |
| Sugar added | A different product | Halva base |
What does grinding fineness change?
It directly affects the speed of separation.
Particles are small in finely ground tahini.
Small particles settle more slowly in oil; Stokes' law explains that.
Separation comes later and less markedly.
Particles are large in coarsely ground tahini and settle fast.
A layer of oil forms within a day or two.
Fine grinding also gives a smoother sensation on the palate.
Stone-ground tahini is generally finer and more homogeneous.
Because a stone mill runs at low speed there is little heating, which preserves the aroma.
The product heats in high-speed grinders and the oil becomes more open to oxidation.
How does temperature affect it?
Temperature determines how freely the oil flows.
In a warm environment the oil is more fluid and separation faster.
In a cool one the oil thickens and separation slows.
Tahini barely separates in a fridge.
But another problem arises: the product hardens and becomes impossible to stir.
Taking it out with a spoon becomes difficult.
Tahini is therefore kept at room temperature.
Somewhere cool and dark is ideal: 15 to 20 degrees.
Separation is faster in summer; that is normal and need not be prevented.
It should be protected from direct sunlight; light accelerates oxidation of the oil and leads to rancidity.
How should it be stirred?
That is the step most often done wrongly.
Stirring from the top with a spoon does not work; the solid mass at the bottom is firm and the spoon does not reach it.
The result is a product very oily on top and very dry beneath.
The right method is turning the jar upside down.
The closed jar is inverted and left for a few hours.
Gravity takes the oil down, that is to the other end of the product.
Stirring then becomes far easier.
A long-handled knife or spatula should be used.
It should reach the bottom of the jar and stir from below upward.
A hand mixer or stick blender can be used too, though in a separate container rather than in the jar.
Once stirred properly the product stays homogeneous for a long time.
Which container suits?
The choice of jar makes managing the separation easier.
A wide-mouthed jar suits best; stirring is easy and the bottom is reachable.
Narrow-necked bottles are impractical; stirring is nearly impossible.
Glass is preferable; it holds no odours and the contents are visible.
Where a metal lid is used its inner face should be coated; tahini is slightly acidic and can contact the metal.
Where the inversion method is used the lid should be confirmed leak-proof.
A large jar can be divided in two; part goes into a small jar for use and the rest stays sealed.
That both eases stirring and reduces contact with air.
How is quality assessed?
There are five criteria.
The first is colour. It should sit between pale beige and light brown.
A very dark colour indicates over-roasting, which brings a bitter taste.
The second is flow. It should pour easily once stirred; a very thick tahini indicates that the oil has not fully come out of the sesame.
The third is taste. A slightly bitter note is normal and comes from the sesame.
But marked bitterness comes either from over-roasting or from rancid oil.
The fourth is smell. It should smell of fresh, roasted sesame.
The fifth is the ingredient list. A single ingredient is best.
Tahini keeps six months at room temperature and a year in a fridge after opening.
A crust forming at the surface comes from contact with air; that layer can be removed and what lies beneath used.
Rancid tahini develops a sharp, paint-like smell; that product should not be eaten.
Which recipes use tahini?
It has a wide range of uses beyond breakfast.
Tahini halva is the best known product, made by combining tahini with sugar syrup.
It forms a basic component of mezes such as hummus and baba ganoush.
Tahini sauce goes into salads and vegetable dishes, thinned with lemon and garlic.
It appears in desserts too; tahini biscuits, tahini cake and tahini çörek are widespread examples.
Some recipes use it in place of fat; tahini brings both fat and protein.
Care is needed in hot dishes; at high temperatures tahini leaves a bitter taste.
Used as a sauce it therefore goes in at the final stage of cooking and does not get boiled.
Whisking it with a little cold water before adding also stops it seizing, which it does readily when it meets hot liquid all at once.
