Instruct: Classify a review into positive or negative sentiment.
Query: Broken jars

I have to echo the complaints of several reviewers about the fragility of the glass cups. After chilling the yogurt and removing the lids from several of the jars, I broke off a large shard of glass. Are the lids simply too tight? Why aren't the jars Pyrex? This is a terrible problem. The yogurt maker itself works all right when the desired yogurt recipe is used. But what good is the delicious yogurt if the glass shatters when you want to use the yogurt?