Christmas baking for science geeks: Pepparkakor Synthesis

Baking is synonymous with Christmas cheer. In Sweden, a favourite Christmas treat is the Pepparkaka (PK) which is a thin, crunchy biscuit flavoured with Christmas spices and enjoyed with Glögg, the Swedish mulled wine. Current methods of Pepparkakor (PK’s) synthesis fail to address the needs of scientists who often required the integration of geekiness into their holiday celebrations. Here, I present a new method for the synthesis of Pepparkakor adapted for scientists and geeks over the festive period.

Materials and methods for synthesis of PK’s
150 ml of syrup
300 ml of brown sugar
200 g of butter
1 large egg
2 tsp of cinnamon
1.5 tsp bicarbonate of soda
800 ml of white flour
300 g icing sugar
Food colouring of choice

Syrup (Hemköp, Stockholm) was added to a small, stainless steel pan (IKEA, Stockholm) and warmed until the viscosity had significantly reduced. The warmed and thinned syrup was then poured over the butter (Hemköp, Stockholm) and the sugar (Hemköp,Stockholm) before being stirred at a frequency 60 revolutions per minute until the butter had melted. The mixture was then incubated at room temperature and allowed to cool to 25°C. During the incubation, the egg (ICA, Stockholm) was extracted from the shell and homogenised. The bicarbonate of soda (ICA, Stockholm) was resuspended in 2 tablespoons of tap water. After the incubation, the egg homogenate, bicarbonate of soda suspension, cinnamon (Hemköp, Stockholm) and flour (ICA, Stockholm) were then all added to the syrup/butter mixture and stirred until a homogeneous mass was obtained. To ensure homogeneity, the mass was worked repeatedly by hand for 2 minutes. The resulting mass was then incubated at 4°C overnight. After overnight incubation, the mass was flattened into a sheet by repeatedly squeezing between a wooden roller (Åhléns, Stockholm) and a hard surface achieving a uniform thickness of 3 mm. Shapes were then stamped out of the sheet either using preformed stamps (Åhléns, Stockholm) or by cutting the required shapes with a knife (IKEA, Stockholm). The shapes were then hardened in a 175°C oven for 8 minutes and then allowed to cool at room temperature to yield the finished PK’s.

To achieve fine detail on the PK’s, icing was made by combining water and icing sugar (Hemköp, Stockholm) in a 3:20 ratio to make a smooth paste. A thin stream of the paste was then created by forcing the mixture through a 2 mm hole in an impermeable polypropylene membrane (Hemköp, Stockholm). Synthetic dyes (ICA, Stockholm) that absorb light at different wavelengths were added to the paste in order to allow visual differentiation between features on the PK’s.

To achieve background colour of the PK’s over a larger area, an icing sugar paste was made using a ratio of 6:20 to create a thinner paste that could be spread more easily. Once the fine detail was completed PK’s were left to dry at room temperature.

I describe a method for integrating science and Christmas by the synthesis of PK’s. PK’s can be used in a stand alone fashion or alongside other traditional Christmas reagents such as Glögg, coffee or tea.



Figure 1. Bacteriophage T4 (A). Blue/white mutant screen on x-gal agar (B). DNA gel with a smear (C). Contaminated streak plate (D). Undigested and digested plasmid prep (E). Either a contaminant or a transformant (F). Half written manuscript (G). Happy and sad scientist with streak plate and gel (H). Western blot (I).

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