If you have ever stood in front of the supermarket fridge wondering whether the salted block on the left will work in the recipe written for the unsalted block on the right, the short answer is this. Most baking recipes are written for unsalted butter so the baker has full control over the seasoning. Salted butter is fine in plenty of bakes, but it carries variable salt levels and slightly more water, which can quietly change a delicate sponge or buttercream. The detail below shows when to swap, when not to, and how to do it properly.
What is actually different between salted and unsalted butter
On paper, the two look almost identical. UK butter must be at least 80 percent fat by law, with the rest made up of water and milk solids. Salted butter simply has salt added during churning. That tiny addition does two things at once.
First, salt is a preservative. Salted butter keeps fresher for longer in the fridge, which is part of the reason supermarkets stock more of it than unsalted. Unsalted butter is more perishable, so it tends to be made and turned over more quickly, and many bakers feel it has a fresher, sweeter cream flavour as a result.
Second, salt brings flavour. Even at low levels it sharpens the dairy notes and balances sweetness. That is wonderful on toast and in shortbread. It is less helpful in a delicate genoise, where the goal is a clean, milky backdrop for vanilla, citrus or cream.
There is also a subtle water question. Salted butter often carries a fraction more water than unsalted, partly because salt is added as a brine in some processes. The difference is small, usually well within the 16 percent water limit allowed in butter, but in pastry and shortcrust where water is the variable that decides between flaky and tough, it can matter.
How much salt is actually in salted butter
This is where most home bakers get tripped up. There is no single industry standard for the salt content of salted butter, in the UK or anywhere else. Each brand sets its own level, and the spread is wider than people expect.
A useful rough rule for UK butter is around 1.5 grams of salt per 100 grams of butter, or about 1.5 percent by weight. Anchor sits near the top end at roughly 1.7 grams per 100 grams. Kerrygold Salted comes in around 1.8 grams per 100 grams. Lurpak Slightly Salted is around 1.2 grams per 100 grams, which is why it tastes noticeably milder than a standard salted block.
Translated into teaspoons, a 250 gram block of UK salted butter typically carries somewhere between 2.5 and 4.5 grams of salt, which is roughly half to three quarters of a teaspoon. That is a meaningful amount in a small bake, especially in cookies, shortbread, scones or buttercream where the added salt in the recipe is usually a quarter teaspoon or less.
Because the figure varies so much, the only safe assumption is that you do not know exactly how much salt is in your salted butter unless you read the label. Recipes written around unsalted butter sidestep that uncertainty entirely.
Why most cake recipes specify unsalted butter
Three reasons, in order of importance.
Control. Recipes are tested with a specific weight of butter and a specific weight of added salt. If the butter brings its own seasoning, the total can drift in either direction depending on which brand you bought.
Flavour profile. Sponges, chiffons, vanilla cakes, white chocolate bakes and most buttercreams want the pure, sweet cream flavour of butter to come forward. Even a low level of salt makes a vanilla sponge taste a touch savoury, which is fine in a sandwich cake but wrong in something delicate.
Consistency. Unsalted butter from any brand will behave more or less the same. Salted butter from one brand can be twice as salty as another. If you bake the same recipe a few times with different supermarket-own salted butters, you will taste the variation.
For these reasons, most professional and recipe development books, including King Arthur Baking's reference material and the work of writers like Stella Parks at Serious Eats, default to unsalted butter as the working standard.
When salted butter is perfectly fine
Plenty of bakes welcome the extra salt rather than fight it. As a working list, salted butter is a sensible choice in:
- Shortbread and biscuits. A clean, salty edge is part of the character. Many traditional recipes were written with salted butter in mind.
- Salted caramel. The salt is the point. You can use salted butter and reduce the added flaky salt slightly, then taste before finishing.
- Cookies with strong flavours. Chocolate chunk, peanut butter, oat and ginger cookies all carry the extra salinity well.
- Savoury bakes. Cheese scones, savoury muffins and savoury tarts where you would have added salt anyway.
- Pastry for savoury pies and tarts. A rough puff or shortcrust for a quiche or savoury galette is forgiving here, provided you skip or reduce any salt the recipe lists.
- Toast, finishing, brushing. Anything painted onto a finished crumpet, scone or loaf.
In all of these, you should still reduce the added salt in the recipe to compensate, especially if the bake is small and the seasoning is concentrated.
When you should not substitute salted for unsalted
Some bakes are sensitive enough that switching is a real risk. Avoid using salted butter in:
- Delicate sponges. Genoise, chiffon, hot milk sponge and classic Victoria sponge all rely on a clean dairy backdrop. Salted butter pushes them off balance.
- Buttercream and frostings. American buttercream, Swiss meringue buttercream, French buttercream and cream cheese frosting all have very small added salt amounts. Even a small overshoot tastes oddly savoury, particularly with white chocolate or vanilla.
- Pound cake and Madeira. These are butter-forward by design. Brand variation in salted butter can swing the seasoning week to week.
- Cookies that depend on flaky salt finishing. If you finish with sea salt flakes for crunch, start from unsalted so the added salt lands on top rather than throughout.
- Recipes with precise small-batch quantities. Anything where the total recipe contains a tiny pinch of salt will be the most vulnerable to butter brand variation.
If your recipe was developed by a careful author with weighed quantities and a specified salt amount, follow it.
How to swap salted and unsalted butter properly
If the only butter in the fridge is the wrong type, there is a workable conversion. The standard rule, used by King Arthur Baking, BBC Good Food and most recipe testers, is roughly a quarter teaspoon of salt per 113 grams of butter, which is about half a cup in US measure.
In practical UK terms:
- If the recipe asks for unsalted butter and you only have salted: weigh out the butter, then reduce the added salt in the recipe by about 1.5 grams (roughly a quarter teaspoon) for every 100 grams of butter swapped. For a typical 250 gram bake that is around 3.5 grams less salt, or about half a teaspoon.
- If the recipe asks for salted butter and you only have unsalted: do the reverse and add about 1.5 grams of fine salt for every 100 grams of butter swapped.
A few sensible cautions:
- Reduce in stages. Cut the salt back by about three quarters of the calculated amount, taste the batter or icing, then top up if needed. You can always add salt; you cannot take it out.
- Use fine salt, not flaky. Flaky sea salt measures very differently by volume. If your recipe specifies fine salt, stick with it for the swap.
- Skip the swap in delicate buttercream. It is rarely worth it. If you have only salted butter and a meringue buttercream on the menu, fetch a fresh block of unsalted before you start.
Choosing a butter for baking in the UK
Beyond salted versus unsalted, a few details quietly affect the bake.
Fat content. Standard UK butter is 80 percent fat. So-called European or premium butters such as Lurpak, Kerrygold and President tend to sit a touch higher, between 82 and 84 percent fat. The extra fat improves richness and helps shortcrust and laminated doughs in particular. For an everyday sponge or cookie, supermarket-own unsalted butter is a perfectly reasonable choice.
Cultured versus sweet cream. Cultured butters such as President carry a tangy, almost yoghurt-like note that some bakers love in buttercream and pastry. It is a flavour preference rather than a technical requirement.
Spreadable blends. Anything labelled spreadable or buttery has had vegetable oil added. These are not butter for baking purposes and will not perform like a block in cakes, biscuits or pastry. Stick to a proper block.
Salt level. If you bake a lot and want one block to cover both salted and unsalted needs, Lurpak Slightly Salted is an unusually mild option that some bakers happily use across savoury and sweet work. It is still not a true substitute for unsalted in delicate recipes, but it is the most forgiving of the salted blocks.
Storage and softening tips that affect your bake
A few quiet habits make a noticeable difference.
- Wrap butter well. Butter picks up fridge smells quickly. Keep it in its original wrapper inside a sealed container or beeswax wrap.
- Soften gradually. Bring butter to room temperature on the counter for an hour or two rather than blasting it in the microwave. Microwave-melted butter behaves differently in creaming and ruins the structure of cakes that depend on aerated fat.
- Cube before creaming. Cutting cold butter into small cubes helps it warm evenly and creams faster with sugar.
- Freeze in usable portions. A 250 gram block can be cut and frozen in 50 or 100 gram pieces, wrapped tightly. For pastry, frozen grated butter often gives a flakier finish than chilled cubes.
The takeaway
For most baking, especially cakes, sponges and frostings, reach for unsalted butter and add salt to taste based on the recipe. For shortbread, cookies, salted caramel and savoury bakes, salted butter earns its place. If you have to swap, weigh the butter, adjust the added salt by around 1.5 grams per 100 grams, and taste as you go.
Want a properly tested example of what a careful butter choice can do? Have a look at our buttercream recipe and the vanilla sponge recipe we use as the base for many of our celebration cakes, or browse our buttercream cakes if you would rather leave the butter ratios to us.