"I am milk that time and bacteria have transformed. I can be fresh and mild or ancient and powerful. Some of me are worth more than gold by weight. What am I?"

Answer: Cheese. Cheese is made by curdling milk and allowing it to ferment and age. Fresh cheeses like ricotta are mild; aged varieties like aged Parmesan or artisan cave-aged wheels develop intense flavour. Rare artisan cheeses can cost hundreds of pounds per kilogram.