How is MEK created?

And could it possibly be the end product of tea leaf fermentation?

Here's a patent that describes one method of forming MEK:

Preparation of methyl ethyl ketone - Patent 4075128 (http://www.freepatentsonline.com/4075128.html)

Basically, you start with secondary butyl alcohol,

CH_3CH_2(CH-OH)CH_3

It's oxidized (with oxygen or another oxidizer) over a catalyst and water is eliminated. The CH-OH group becomes C=O.

You can also oxidize the alcohol to a peroxide and then decompose it. There seem to be a number of patents and papers that do it that way.

You can also dehydrogenate the alcohol over a catalyst. In this reaction, you would form the ketone directly and hydrogen would be the byproduct. This seems to be popular also.

Now, as to whether it's the end product of tea leaf fermentation, I can't say. I don't know what's involved in that.