Can salted butter be used to make lemon curd?

Often, at least in the US, recipes will specifically call for unsalted butter, then call for salt to be added to the recipe — which causes many to scratch their heads.

There are three main uses that come to my mind for salt. One is to impart a salty taste. The usage in butter is primarily a secondary one, and that is as a preservative. The third is as a flavor enhancer (which can also apply to butter, but to my knowledge is not the primary reason there). Many recipes that call for a small amount of salt are using it strictly as a flavor enhancer. The intent is to highlight other flavors without actually tasting the salt.

So why call out unsalted, then add salt? Two reasons that I know of. The amount of salt in salted butter varies. If you read the label carefully and do the math, you might get a rough idea, but in general by just picking up the butter you do not know how much salt is in there. Some may have enough to taste, others you may not notice. By using unsalted, you are in control of how much salt is added and can even adjust to taste as individuals who practice a lower-salt diet tend to taste it at lower amounts. Higher-salt diets tend to become numbed to the taste so do not notice it at lower amounts. This contributed to the older tendency to call for a "pinch" and a pinch varied from person to person according to their own sense of taste.

The second reason is more subtle. Salt in butter is a preservative. Since it has salt, it tends to hold up longer in storage. Since it holds up longer, there is at least a perception that salted butter may be older. So calling for unsalted by some cooks and authors can be like saying "use fresh butter, not old." It is an old tendency, and many may not even realize that is an origin, even if subtly implied.

Now, not knowing your curd recipe, it may not call for added salt. I come from a high-salt background, so it is unlikely I would taste the difference, while others might. In the case of your particular recipe, there may be a tendency for at least some people to actually taste the salt, especially given that the amount of salt in the butter may vary by maker.

Using salted butter would result in a perceivably salty curd - probably not what you want when expecting a sweet lemon curd. The general rule of thumb is to use unsalted butter for sweet dishes and cakes, especially when the butter makes up a significant percentage of the whole dish.

The reason why some recipes simply state “butter” is that not all locales consider salted butter as the default. For example: In Germany (where I live), “butter” means unsalted, and salted butter is a specialty item, which may even come at a higher price. In the US it’s the other way around.

From what I observed, the UK (homeland of the lemon curd) is something in between - sometimes explicitly, sometimes implicitly calling for unsalted butter for baking and deserts.

I disagree with Stephie's answer above. I find using salted butter does not give a perceptively salty taste but instead helps to bring out the lemon flavour. A pinch of salt or salted butter is recommended in The Kitchen Magpie and Guardian perfect lemon curd.

Of course, as Luciano says, if you use unsalted butter you have more control, but I don't think it is necessary to buy it specifically for lemon curd.

In response to a comment: this is based on using salted butter with 1.7g of salt per 100g of butter.

• For cooking in general it's usually better to use unsalted butter. You can always add more salt if needed (and in the correct amount) but it's not easy to control the salt properly if you have to add more butter. So your lemon curd could be ok but it might taste slightly funny, depending on the amount of salt in your butter.
• Butter can be frozen for months, so if you don't want to use unsalted butter all the time you can just defrost the amount you need before using.
• For most recipes always assume it uses unsalted butter, unless specified otherwise. Specifically sweet recipes, where salt is not always required.

It depends on how much butter the recipe calls for relative to other ingredients--and what those other ingredients are.

Amount of butter: How much butter matters? Usually if the taste or texture of the final product is buttery then there's enough butter in it that the salted-ness of the butter matters. On the other hand, if the final product does not obviously contain butter, then the total amount of salt from the butter will be less important. For lemon curd, there's usually no butter flavor or texture in the result.

Other strong flavors: If you have other strong flavors, they can mask the salt. (In this case, the lemon and sugar are both going to be really strong.)

Amount of added salt or salty ingredients: If the recipe already calls for added salt, you can reduce that to compensate for salted butter. Or if there are other salty ingredients, then a little more salt from the butter will be less noticeable.

Conclusion: For lemon curd, you're probably fine with salted butter, just reduce any salt that's added in the recipe.

Bonus suggestion: If it's just butter that's expensive in your area, there are recipes for vegan lemon curd (no butter, no eggs) or dairy free lemon curd (vegetable oil or coconut oil (tastes like lemon-coconut)) that you could try instead of a traditional recipe.

Salt can have a physical effect on certain ingredients. Some fruits and vegetables start to lose their water through osmosis when they get in contact with salt. Depending on the recipe, additional moisture in the pan might or might not be desired during certain phases. This can be a reason for specific instructions regarding when to add how much salt to the dish.