I mentioned in my Creative Baking: Macarons book that you can't reduce the amount of sugar in macaron shells as sugar is required for structural stability. This is technically true if you just reduce the amount of sugar without any replacement. I tried to do a search for reduced sugar recipes but have not found any that is lower than the ratios I use. However, I found that it is common for people to substitute almond meal with rice flour to make macarons for nut allergy sufferers. Macaron purists will protest and say that those are not really macarons but it did give me an idea to try using rice flour to substitute part of icing sugar. You can't just take away sugar from the recipe without substituting with something else that will help with structural stability. Rice flour is gluten-free and would produce a more melt-in-your-mouth texture than wheat flour (cake flour, plain flour, pastry flour).
*Update (20/4/16): Cornflour can be used instead of rice flour too! But I personally prefer the rice flour version texture wise as it is more delicate. The cornflour version is chewier. I tried using a ratio of 3:1 for rice flour: cornflour and it works well :). Cornflour helps the shells to dry faster whereas rice flour gives the shell a nice delicate melt-in-your-mouth texture. The issue I had with rice flour alone is it seems to extend the drying time required.
Besides substituting part of the icing sugar, I have also reduced the amount of meringue used (and therefore less sugar) as I find that the mass does not need that much meringue for this combination. Adding too much meringue results in a runnier batter. So instead of the usual ratio 1.25:1.25:1.25:1 for almond(plus rice/corn flour if using):icing sugar:caster sugar:egg whites, I used 1.47:1.2:1.2:1. I am pleased to say that the resulting texture is about the same as regular macarons without rice flour. I have also added a bit of salt to counter the sweetness. You may substitute a larger percentage of icing sugar with rice flour but I personally prefer not to deviate too much from a tried and tested ratio. Afterall, nothing beats sugar when it comes to melting in your mouth. Macarons are like delicate candies and one is not supposed to have too many at one shot so don't be too hung up about the high sugar content. Just use tea flavours, cocoa, sour fruits or salty fillings to counter the sweetness and you will have a delectable little treat :).
Here's a photo of the cross-section of a macaron to prove that the texture is still lovely. Crisp thin outer shell, soft fluffy and only slightly chewy interior. No hollows.
Recipe for reduced sugar macaron shells
200g superfine almond powder/meal
180g icing sugar
20g rice flour
1/8 tsp fine sea salt
78g egg whites*
Rose pink and dusty rose gel food colouring (or whatever colours you want)
72g egg whites*
180g caster sugar
1/4 tsp cream of tartar (optional)
*preferably aged but not necessary
Updated recipe (22/4/16)
I have used this quite a few times with much success although the percentage of sugar replacement is less than my earlier attempts. Having said that, this recipe of 300g almond meal contains 40g less sugar overall than what the traditional recipe calls for. Please scale the recipe accordingly as I am using this for my big batch of 800 macarons. This recipe can make about 110 macarons. If you feel brave enough to experiment, you may increase the amount of icing sugar substitution with rice and cornflour.
300g superfine almond powder
280g icing sugar (without cornflour. If you only have icing sugar with cornflour added, I suggest halving the amount of cornflour and replace with rice flour instead.)
15g rice flour (2 tbs, I included measurement in spoon so that it is easier to scale down)
5g cornflour (2 tsp)
1/8 tsp fine sea salt
118g egg whites
Powder or gel food colouring
112g egg whites
280g caster sugar
1/4 tsp cream of tartar (optional)
1. Prepare baking trays with circle templates. Place baking paper over template. Stick the baking paper to tray later with a bit of Italian meringue or macaron batter when you have made it.
2. Prepare the mass. Sift almond, rice/corn flour, icing sugar and salt together into a large mixing bowl. Add egg whites and mix well with a spatula. Divide into two or as many portions as you like if making more than one colour. Remember to weigh the mass for each colour. Add the colouring. Powdered or natural sources of colouring may also be added at this point.
3. Prepare Italian meringue. Heat caster sugar and water in a small saucepan until 115°C. In the mean time, beat the egg whites (with cream of tartar if using) with electric mixer at medium low speed until soft peaks form. Reduce mixer speed if necessary if temperature of syrup is not reached. Once temperature is reached, increase mixer speed to medium high and carefully pour the syrup in a thin stream into the egg whites, avoiding the beaters. Continue beating for another 10-12 minutes until the meringue is stiff, glossy and cool. Portion out the meringue for various colours according to the formula: weight of meringue = 0.51 x weight of mass
4. Macaronage. Fold the meringue into the mass in two additions until the batter moves in a lava-like way. Please refer to this post for the macaron basics on folding and testing batter consistency.
5. Transfer batter into piping bag fitted with 6-7mm diameter tip (Wilton #12). Pipe the various circles. Bang tray on table to remove trapped air. You may use a toothpick to pop any stubborn bubbles. Here's a video on how to pipe larger shells (10cm and above) using the trace-and-fill technique which is also shown in the book and in this post. You may use whatever way to pipe the circles actually :). Just do what you are comfortable with.
Piping a 13cm diameter macaron shell
Here are all the different sizes of shells...
6. Let the shells dry under the fan in aircon room until dry to touch. Drying time can range from 30 minutes - 2.5 hours depending on humidity.
7. Preheat the oven near the end of drying time. Set the oven rack to lowest position. Bake the shells according to the following time and temperature. Note that this is a guide as each oven is different. Remember not to use the fan mode during baking. It will cause lopsided feet and even cracked shells. Check that the feet are dry for doneness. Let the shells cool completely before removing from baking paper.
13cm diameter: 140°C for 15 minutes, 130°C for 10 minutes, 20-25 minutes at 115°C
10cm diameter: 140°C for 15 minutes, 130°C for 5 minutes, 115°C for 15-20 minutes.
6cm diameter: 140°C for 10 minutes, 130°C for 5 minutes, 115°C for 10-12 minutes
3.5 and 2.5 cm diameter: 135°C for about 18 minutes.
I hope this has been an informative post!
Update 19/1/17: if you prefer using the French method, checkout this post for the reduced sugar version for French method!