On a Lemon Curd Mousse Experiment

I have always said that science isn’t really my thing. In school and then university I liked history, humanities, social sciences, and quite liked math(s) even, but oh no, not science. I did one year of physics in high school which I think is more than enough torture for your average human. Biology – I did that one all the way through first year university. But no chemistry. None. Which is ironic for 2 reasons:

• The man studied chemistry and indeed has a degree in it.
• As a caterer I spend a good proportion of my life cooking and baking. And what is cooking and baking but science? Food chemistry to be more precise.

Isn’t life funny that way? A self proclaimed science phobe paired up with a science lover, working every day with the chemistry of food. Which is fascinating science in my mind (though thankfully from what I can tell there is no physics involved). I love experimenting with recipes, trying new techniques, changing methods used when cooking for a family to methods necessary when cooking for 100 or more people. It’s about taking a problem or question, developing a hyphthesis or two about how it might work or could be done, and then testing it.

I recently gave myself a problem to solve: develop a fresh lemon curd cream filling for a large tart (that would be covered with fresh strawberries) that would hold its structure (more or less) when sliced. Simple, no? Well, sort of…

I make lemon or lime curd cream almost every week these days, but generally as a filling for pavlovas or small tartlets. And as thick as it may be when I first make it, it loses structure fairly quickly. I think it may be the acid in the curd that causes that to happen. This is fine in a pavlova as the cream is supposed to be soft and floppy. And in an individual tartlet there is nothing wrong with light, silky, slightly floppy cream. But in a big tart this soft, floppy fresh cream filling just won’t do – it’s difficult to serve and doesn’t look very nice when it starts to ooze or flop all over the place.

The cream in these is as light as air but can be messy when you take a bite

So the challenge was on: develop a lemon curd cream/mousse like filling for a large tart that would hold its structure for minimum 24 hours.

But how? I scoured in internet for information and recipes, and in the end fell back mostly on one of my most well loved cookbooks (and believe me, it looks it!): The Cake Bible by Rose Levy Beranbaum. Honestly, if you’re at all into cakes this book is an absolute kitchen essential (read more about it here). Anyway, I did my reading, came up with 3 different recipes/methods to test, made my lemon curd, bought ingredients, and set out to experiment.

Lemon, lemon & more lemon (and some cream too...)

My 3 methods were as follows:

1. Add mascarpone to the cream to make it thicker (and more stable?)
2. Whip the cream in the food processer – less air is incorporated into it therefore it would be more stable, wouldn’t it?
3. Add a small amount of gelatin to the mixture

Left to right: methods 1-3

With my small helper (which I’m not sure I’d advise if trying to be scientific and precise) I made the 3 types of lemon curd cream (or mousse as I was now calling it), put them in the fridge, and told the man, boy & girl in no uncertain terms that they were not to touch those enticing glasses of lightest yellow cream until the next day. Sheepishly, I will admit that I regularly dipped a wee finger in to test the texture over time – but all in the name of science of course.

So the result:

Method 1 (add mascarpone) was the lightest, but lost structure and was quite floppy after 24 hours.

Method 2 (whip cream in food processor) was not as light as Method 1, held its structure fairly well, and had a soft, creamy mouth feel.

Method 3 (add gelatin) was the most mousse-like in texture and held its structure very well. It wasn’t as soft and creamy as method 2 – it was much firmer.

All in the name of science

As far as science experiments go, you could do far worse than experimenting with lemon curd, cream, and a few other items. I’m still undecided as to which I will use when I make my large tarts – I’m torn between methods 2 and 3. Either way, topped with fresh berries of the season they will taste really quite divine.

Lemon Curd Cream/Mousse

Method 1:

• 250 ml double cream
• 175g mascarpone cheese
• 2 tsp powdered sugar
• 125 ml lemon curd

Whip cream until you can just see the beater marks in the cream. Add the mascarpone and powdered sugar and whip until soft peaks form. Fold in the lemon curd with a balloon whisk until well combined (the cream will stiffen as you continue beating). Use immediately.

Best uses: for pavlova (large or individual) or for individual tartlets.

Method 2:

NB: You will need a food processor for this one.

• 500 ml double cream
• 2 tsp powdered sugar
• 125 ml lemon curd

Whip the cream and powdered sugar in a large food processor bowl fitted with the normal blade. When it’s softly whipped (i.e. soft peak stage) fold in the lemon curd. You can fold in the lemon curd with your food processor but do it using very short pulses or else you will end up with lemony butter! Use immediately.

Best uses: pavlova, individual tartlets, large tarts, cakes

Method 3:

• 2 leaves (platinum grade) gelatin
• 4 tbsp water
• 500 ml double cream
• 2 tsp powdered sugar
• 125 ml lemon curd

Break up the gelatin leaves in a small bowl and cover with the water. Leave for 10 minutes to soften. Set the bowl in gently simmering water. Stir occasionally until the gelatin is dissolved. Remove from heat and leave to cool for 5-7 minutes (the gelatin must be cool but not really starting to set).

Whip cream until you can just see the beater marks in the cream. Add the gelatin mixture and powdered sugar and whip again until soft peaks form. Fold in the lemon curd (the cream will continue thickening as you fold). Use immediately.

Best uses: large tarts, desserts such as joconde sponge (see here), roulades, cakes with a thick layer of filling, piping