What is the fine-grained topic of the following text: When winemakers Alexander Byrne (of Lethbridge Wines) and Sam Vogel (Provenance Wines) heard a friend from high school, Cam Nicol had found a concrete wine fermenter underneath his house, they did what any sane person would do and ordered half a tonne of Shiraz grapes. Only return the topic.
Making wine using a found concrete fermenter