My mother did the same thing with her sourdough starter. She had some she had kept going for decades, put the Tupperware in the oven away from drafts and forgot it was in there and turned on the oven. Dead starter and plastic melted all over the oven. I managed to melt an aluminum clad pot on my stove and was fortunate enough not to burn down my house. Only had to replace the element on the stove.

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