Using reporting guidelines to improve the reproducibility of cooking Christmas tree meringues: the “People tasting trees” cluster-randomised controlled trial

Objectives: To test whether improving a Christmas tree meringue recipe using reporting guidelines yields more appealing and sweeter meringues. Design: A prospective, superiority, single-blind, cluster-randomised (1:1) controlled trial Setting: A public participatory event in a large cultural facility in France Participants: Budding chefs with basic culinary skills, possessing the utensils necessary for baking Christmas tree meringues, and not having burned pasta in the past month (for safety reasons).Interventions: Each budding chef was randomised to a standard recipe for making Christmas tree meringues or to the same recipe written in consultation with a professional baker using the TIDieR checklist - a reporting guideline for description of complex interventions - plus a short video tutorial.Main outcome measures: The primary outcome was reproducibility in terms of visual aspect as rated by an independent jury which compared the cooked Christmas tree meringues with the recipe picture on a scale from 1 to 10. Secondary outcomes included colour, size, taste and survival time in the course of a sale organised as part of the public event. Analyses were performed in intention-to-eat (randomization unit: budding chefs / analysis unit: Christmas trees). Results: 60 budding chefs (30 in each group) baked a total of 845 Christmas tree meringues. There was no significant difference between the groups (mean difference=-0.1; [95%CI -0.99; 0.80]; p-value=0.84; intra-cluster correlation, ICC=0.77) on visual aspect. No difference was found for reproducibility in terms of colour (mean difference=-0.31; [95%CI -0.97; 0.35]; p-value=0.35; ICC=0.67) or size (mean difference=-0.17; [95%CI -1.07; 0.73]; p-value=0.71; ICC=0.74). There was no significant difference in terms of taste between the groups (mean difference= -0.55; [95%CI -1.62; 0.52]; p-value=0.31). 400 meringues were sold during the public event with no difference in survival time between groups (hazard ratio= 1.26 [95% CI 0.75–2.09], p-value=0.38) in favor of the control group. Conclusions: Our study failed to demonstrate that an improved recipe using the TIDieR reporting guideline with a video tutorial improved the reproducibility in terms of visual aspect, colour, size, taste and sales for Christmas tree meringues. The best way to succeed in baking Christmas tree meringues - and thereby to improve reproducibility of experiments - remains a mystery still to be solved by further explorations. Trial registration: https://osf.io/dnhbx