Why does freshwater fish taste muddy?

​What makes freshwater fish taste muddy? M. Rundle

More than 20 years ago, I covered a story on the last of the Murray cod fishermen. He was out near Barham in the south of NSW. The photographer and I went with him in his boat to his nets, where he pulled out a decent-sized female. He was sharing that one with us. He cleaned the fish and showed its insides. The lining of the abdomen was covered in an intricate meandering pattern. He said that Indigenous Australian lore has it that this was a map of the river in which the fish lived, and that is how it navigated the waterways. We steamed the fish, and it was sweet, its internal fat luscious. It tasted of the water in which it lived, with a faint earthy note. Some call it muddy. It is not mud. It is a compound called geosmin, formed when bacteria that are in the water munching on organic matter such as fallen leaves die. Their micro corpses release geosmin, which is consumed by fish and accumulates in darker muscles and in the fat under their skin. Humans are incredibly sensitive to geosmin; we can detect it at one part per billion. It is not harmful but is very sensitive to acid. If you find yourself with a muddy-tasting piece of carp, cod, prawn or yabby, souse it in lemon juice, and it will eliminate the muddy aroma.

I cook for our Monday meeting at work each week and enjoy trying out new recipes. My question is, if I bake a cake with alcohol, will I make the team tipsy? B. O'Sullivan

Not a good idea to get your work colleagues drunk, especially if you work in a hospital surgical team. A council planning department or banking investment office? Not so important, but definitely don't get anyone drunk in a job where lives are at risk. That said, ethanol alcohol has a low vapour point of just under 80 degrees. When you flambe brandy or wine in a pan, for example, 75 per cent of the alcohol evaporates and burns off straight away. But the issue is that brandy and wine are not pure ethanol. There's a lot of water in wine, brandy and liqueurs. The water affects the ability of alcohol to vapourise. After 15 minutes of simmering, only 60 per cent of the alcohol in a braise will have evaporated. After two and a half hours, there will still be 5 per cent alcohol in the stew. When it comes to baking, if the alcohol is stirred through the batter, a fair amount will remain after baking. Of the alcohol added to cake batter, after 30 minutes of baking, 35 per cent will remain in the finished cake. Although that amount of alcohol would not affect most people, I'd play it safe and keep your baking teetotaller.

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