本文选自雅思听力Section 4，难度较大

Summary:味精是许多人在烹调的时候会使用的调料，但却很少有人了解它的历史。实际上，许多种调料在进入人类的厨房之前都经历了一个复杂而又曲折的过程。味精也是一样，它最先是由人们在一种还槽中提炼出来的。

HINTS
kombu
glutamate
MSG

全文听写，英式拼法

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But it wasn't until 1908 that the ingredient in kombu which was responsible for the improvement in flavour was actually discovered to be glutamate by scientists working there. From 1908 until 1956, glutamate was produced commercially in Japan by a very slow and expensive means of extraction. It was in 1956 that the speed of the process was improved, and industrial production increased dramatically and still continues to increase to this day. In fact, hundreds of thousands of tonnes of MSG are produced all over the world today.