I can provide some general information that might help you understand the potential reasons for the sour taste.
Fermentation occurs when microorganisms, such as wild yeasts or bacteria, break down sugars and starches in food. If your cake had any ingredients that contain natural sugars, such as fruits, fruit juices, or even certain dairy products like yogurt or sour cream, they could contribute to fermentation over time.
When a cake is not stored properly (e.g., left out at room temperature without refrigeration), the warm and moist environment can facilitate the growth of microorganisms, leading to fermentation. As a result, the sugars in the cake can be converted into acids, causing the sour taste you experienced.
Additionally, if your chocolate cake had any frosting or fillings that contain dairy products, they might have turned sour due to spoilage. Dairy products are susceptible to spoilage if not stored at proper temperatures.
It's essential to follow food safety guidelines to prevent spoilage and foodborne illnesses. If you notice any signs of spoilage, such as a foul smell, unusual texture, or off-taste, it's best not to consume the food.
In summary, if your chocolate cake tasted sour after being left out at room temperature, it's possible that fermentation or spoilage occurred due to the presence of certain ingredients. To prevent such issues in the future, always store perishable cakes and desserts in the refrigerator and consume them within the recommended time frame.