Do I have to brush syrup on a cake at all?

Not on a butter cake, which usually carries enough fat and moisture already. Soaking matters most on lean sponges such as genoise, which are built on whipped egg rather than butter and are noticeably dry without it. It also helps any cake that has been baked ahead and frozen, where some moisture is lost in the process.

When should I brush the syrup on?

On the cut faces, once the layers are cool and levelled, just before filling. Brushing a warm cake makes the surface gummy, and brushing after filling gets syrup on the buttercream. Use a soft brush and go over the whole face twice lightly rather than once heavily, so it absorbs evenly instead of pooling.

What is Brix and do I need to measure it?

Brix is sugar as a percentage of the total weight, so a 1:1 syrup by weight is 50 Brix. You do not need to measure it, because if you weighed the sugar and the water you already know it. It is worth knowing the term because pastry recipes and syrup specifications often quote Brix rather than a ratio.

How long does simple syrup keep?

A 1:1 syrup keeps for several weeks refrigerated in a clean sealed jar, and a richer 2:1 keeps longer because the higher sugar concentration is less hospitable. Flavoured syrups with fruit or dairy in them are a different matter and should be treated as perishable. If a syrup looks cloudy or smells at all fermented, discard it.

Batter and baking

Sugar Syrup and Soak Calculator

Simple, light and rich syrup ratios by weight, with the Brix figure and how much soak a cake takes.

Quick answer

Simple syrup is 1 part sugar to 1 part water by weight, which is 50 Brix. For 500 g of syrup that is 250 g of sugar and 250 g of water. A light soaking syrup at 1:2 moistens without sweetening much, and a rich 2:1 suits a cake that has to sit.

Syrup

Total syrup wanted (g)

Cake to soak

Layers to soak

Result

250 g sugar, 250 g water

a 1:1 syrup at 50 Brix

Every figure, with what it is based on
Figure	Value	Basis
Sugar	250 g	Derived from the ratio
Water	250 g	Derived from the ratio
Ratio by weight	1:1	Trade convention
Brix	50 Sugar as a percentage of the total weight	Derived
What it suits	The default soak, and the base for most flavoured syrups	Trade convention
Syrup that cake will take	About 55 g A sponge takes far more than a butter cake	Trade convention

Brix = sugar weight / total weight x 100

Brix is derived arithmetic: it is simply sugar as a percentage of the total. Which ratio suits which job is trade convention, and shops differ widely on how heavily they soak.

The formula

Brix = sugar weight / total weight x 100

Brix is simply sugar as a percentage of the total weight, so it falls straight out of the ratio and needs no measuring instrument to know. A 1:1 syrup by weight is 50 Brix by definition.

Which ratio to use is a matter of the job. A lean sponge wants a light syrup because it needs moisture more than sweetness. A cake that has to sit for a day or two takes a richer one, because sugar holds water in the crumb.

How much a cake takes varies enormously, and shops differ widely on this. A genoise or other lean sponge takes far more than a butter cake, which is already moist enough not to need much at all.

Derived, published or convention?

Brix is DERIVED arithmetic. The ratios and which job each suits are TRADE CONVENTION, and the quantity a cake takes is convention with a very wide spread between shops.

Syrup ratios by weight
Syrup	Sugar to water	Brix	For 500 g total	What it suits
Light soaking syrup	1:2	33.4	167 g sugar, 333 g water	Moistening a lean sponge without sweetening it much
Simple syrup	1:1	50	250 g sugar, 250 g water	The default soak, and the base for most flavoured syrups
Rich syrup	2:1	66.6	333 g sugar, 167 g water	A heavier soak for a cake that has to sit, and for glazing

Ratios are by weight, not volume. Brix is derived directly from the ratio.

Gear for these numbers

These are rendered from the verified catalog and re-ordered against your numbers once you calculate.

Beginner

Etekcity

Etekcity Food Kitchen Scale, 11 lb, Grams and Ounces

$13.99

The cheapest scale worth buying, and owning any scale at all is the single biggest accuracy improvement available to a home baker.

Best for: a first kitchen scale

Check price on Amazon

Amazon prices move often, so check before you buy.

Beginner

Taylor

Taylor Programmable Digital Candy and Deep Fry Thermometer

$12.49

It clips to the pan and alerts at a set temperature, which is what you want for Italian meringue syrup because the window between 238 and 248 F goes past quickly.

Best for: Italian meringue syrup and sugar work

Check price on Amazon

Amazon prices move often, so check before you buy.

Intermediate

OXO

OXO Good Grips Silicone Heat Resistant Spatula Set, 3 Piece

$23.95

Heat resistant silicone is required for Swiss meringue over a bain-marie, where a plain rubber spatula degrades and leaves marks in the bowl.

Best for: folding batter and working over heat

Check price on Amazon

Amazon prices move often, so check before you buy.

Questions people ask

Do I have to brush syrup on a cake at all?: Not on a butter cake, which usually carries enough fat and moisture already. Soaking matters most on lean sponges such as genoise, which are built on whipped egg rather than butter and are noticeably dry without it. It also helps any cake that has been baked ahead and frozen, where some moisture is lost in the process.
When should I brush the syrup on?: On the cut faces, once the layers are cool and levelled, just before filling. Brushing a warm cake makes the surface gummy, and brushing after filling gets syrup on the buttercream. Use a soft brush and go over the whole face twice lightly rather than once heavily, so it absorbs evenly instead of pooling.
What is Brix and do I need to measure it?: Brix is sugar as a percentage of the total weight, so a 1:1 syrup by weight is 50 Brix. You do not need to measure it, because if you weighed the sugar and the water you already know it. It is worth knowing the term because pastry recipes and syrup specifications often quote Brix rather than a ratio.
How long does simple syrup keep?: A 1:1 syrup keeps for several weeks refrigerated in a clean sealed jar, and a richer 2:1 keeps longer because the higher sugar concentration is less hospitable. Flavoured syrups with fruit or dairy in them are a different matter and should be treated as perishable. If a syrup looks cloudy or smells at all fermented, discard it.

Worked out for you already

A note on what this can and cannot tell you

This calculator does arithmetic on the numbers you give it. It does not know your oven, your recipe or your altitude. Figures are labelled as derived, published or trade convention, and where no honest figure exists the calculator says so instead of producing one. Researched guidance, not professional advice.