Whenever a new, potentially controversial technology enters public awareness, stakeholders suggest that education and public engagement are needed to ensure public support. Both theoretical and empirical analyses suggest, however, that more information and more deliberation per se will not make people more supportive. Rather, taking into account the functions of public sense-making processes, attitude polarisation is to be expected. In a real-world experiment, this study on synthetic biology investigated the effect of information uptake and deliberation on opinion certainty and opinion valence in natural groups. The results suggest (a) that biotechnology represents an important anchor for sense-making processes of synthetic biology, (b) that real-world information uptake and deliberation make people feel more certain about their opinions, and (c) that group attitudes are likely to polarise over the course of deliberation if the issue is important to the groups.