Black treacle
The dark, bitter, strongly acidic end of the syrup range — and the acidity is what makes it react with bicarbonate of soda.
Also called molasses (US); blackstrap molasses (US) — The most concentrated grade, more bitter and less sweet than British black treacle. Not interchangeable by taste even though both are the same class of product.; what does black treacle do in cakes (UK)
Black treacle is what remains after sugar has been crystallised out of cane juice. It is dark, viscous, only moderately sweet, distinctly bitter and — the property that matters most in baking — acidic.
That acidity does chemical work. It reacts with bicarbonate of soda to produce carbon dioxide, which is why gingerbreads, parkin and treacle-heavy fruit cakes are so often leavened with bicarbonate rather than baking powder. Substituting a neutral syrup into such a recipe removes the acid the leavening depended on, and the bake rises poorly.
It is also strongly hygroscopic, so treacle-rich bakes stay moist and often improve over several days — the reason parkin is traditionally kept before eating.
Its flavour is assertive enough to dominate. Most recipes use it alongside a milder sugar rather than alone, and swapping it for golden syrup one-for-one gives something far paler, sweeter and less interesting than intended.
What changes if it is left out
Nothing reproduces it. Dark muscovado sugar is the closest in flavour and brings less acidity and no liquid; golden syrup replaces the liquid and none of the character. Where bicarbonate of soda was the leavener, removing the treacle removes the acid and the rise with it.
Follows from the acidity and hygroscopicity recorded here and from the acid-base leavening model, which carries its own support.
RecordedFollows from evidence recorded elsewhere on BakeHQ
Related
What it does
pH modification
THE FUNCTION THAT MATTERS MOST. Treacle is acidic enough to react with bicarbonate of soda, which is why gingerbread and parkin are leavened that way and why swapping in a neutral syrup flattens them.
Moisture retention
Strongly hygroscopic, which is why parkin is traditionally kept for several days before it is eaten.
Covered in
The sugars, and when the difference matters
The acidic extreme, and the reason gingerbread uses bicarbonate of soda.
Used in
Colour and depth in the rich British form.
Colour, bitterness and depth in the darker forms.
Compared in
Golden syrup vs treacle vs molasses
One side of the comparison.