Truffle, smell

Truffles contain lots of small organic molecules, especially alcohols, aldehydes and ketones, such as 2-methylpropanal, butanone, 2-methylpropan-l-ol, 2-methylbutanal, 3-methylbutanal, 2-methylbutan-l-ol and 3-methylbutan-l-ol. However, the truffle smell is due to sulfur-containing molecules, most notably CH3SCH3 (dimethylsulfide), as well as CH3CH2CH2SCH3 and CH3CH=CHSCH3. 

For all of recorded history mankind has located and identified certain items by their aroma. Whether it is a dead mouse in the closet or a freshly baking loaf of bread in the oven, we often make the identification correctly without seeing or touching the item. We have considered this sense so useful that when we find our own sense of smell to have inadequate sensitivity for a certain task we often borrow the more acute sense of smell from some animal. For centuries we have used dogs for hunting and pigs for truffle harvesting. 

Virtually all people lack the ability to detect some specific odors. A striking example of such an anosmia is the inability to smell the volatile steroid androsten-one (5a-androst-16-en-3-one), a constituent of perspiration, of some pork products, truffles, and celery.922... 

The first organosulfur compounds in this book were the dreadful smell of the skunk and the wonderful smell of the truffle, which pigs can detect through a metre of soil and which is so delightful that truffles cost more than their weight in gold. 

Several sulfur compounds have been detected as volatile constituents of truffles. 2,4-Dithiapentane is a major component of the volatile aromatic compounds of the Italian white truffle, Tuber magnatum. Over 120 compounds have been detected in the black Perigord truffle, T. melanosporum. These include dimethyl sulfide, 2-methylbutanol, 2-methylpropanal and2-methylpropan-l-ol. The nutty and earthy flavour is attributed to anisoles and polymethoxybenzenes. Truffles also produce a volatile steroid, androst-16-en-3-one (7.67), which when more concentrated has an unpleasant smell. The combination of these compounds produces an odour that is a powerful animal attractant. The capacity of animals to detect the presence of underground black truffles by these substances has been evaluated by burying samples of the different compounds. The animals located the dimethyl sulfide lure as well as the black truffle flavouring. 

At one time, it was believed that they were detecting the smell of 5a-androst-16-en-3a-ol, a steroid which has been identified in truffles and is also present in boars saliva. It was thought that the pigs were conditioned to responding to a pheromone molecule. 

On keeping the truffle, the volatile sulfur compounds evaporate faster than other molecules. After a while, the smell becomes mushroomy and is now mainly due to l-octen-3-ol, the principal compound responsible for the smell of mushrooms (it is known as mushroom alcohol ) as well as the related l-octen-3-one, which also has a mushroom smell (see p381). 

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