Fornacalia was a moveable feast and its official date was posted each year in the Forum. In early Rome, it was likely determined by the new moon, which was the first day of the month which Roman priests announced from Capitoline Hill. And as spring began officially somewhere between February 5th -7th, (also the beginning of Fornacalia) I also think it likely this festival is a remnant of fertility magic associated with much earlier goddesses who from Old Europe to Mesopotamia, were associated with grain, bread, and baking. Their shrines and temples often featuring communal oven at the centre, a symbolic representation of the womb of the Great Mother.
Fornax can be roughly translated as the phrase “the Oven is the Mother” and her rites called the Fornalacia were once so important that every citizen in Rome was expected to attend. Ovens were draped in garlands, spelt and grains were toasted and offered to Fornax in order that she bless the ovens, ensuring that bread is properly baked and not burnt in the coming year. This nine-day festival concluded on February 17th with a grand “Oven Feast” during which everyone ate and drank profusely.
Details are scant about what exactly was eaten during the Fornaclia feast but there surely had to be plenty of bread. Bread and cakes featured heavily in many Roman religious rites involving goddesses from Ceres, Diana to Vesta. Loaves were most often round or shaped into body parts, hands, breasts, ears, eyes, and consumed in religious feasts on the respective seasonal holidays and festivals of each goddess.