他们是用的什么把饲料煮得带有酸味的？

What do they use to sour the mash?

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酸乳酪一种具有酸味的蛋奶糕状食物，由细菌作用的牛奶凝结物制得，尤指。

A custardlike food with a tart flavor, prepared milk curdled by bacteria, especially Lactobacillus bulgaricus and Streptococcus thermophilus, and often sweetened or flavored with fruit.

youdao

黑咖啡也有酸味，适当的热作用产生适度的酸味，将可使咖啡的味道更佳，让人觉得更有深度。

Black coffee has sour taste, the appropriate role of generating moderate heat sour, would provide the coffee taste better, people feel more depth.

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