The Use of Cacão Beans as Currency

Submitted by Ron Catterall.  This is an example of the sort of comment that form a 'topic'.  I'm not at all sure just how serious this discussion of currency is.

Many people have referred to the use of Cacão beans as currency, and indeed there are illustrations showing (apparently) sacks of something that might be beans in a position that might be a 'point of sale'.  Some points that occur to me:

• A system of barter - how much of 'this' for how much of 'that' is not realistic - it does not scale well.  For example, for two items only one exchange rate is needed, for 3 items, three, for 4 items 6, for 5 items 10, for 6 items 15 and for 10 items 45 different exchange rates are needed.  In general, for 'n' items, a total of (n-1)+(n-2)+(n-3)+...(n-n) exchange rates are needed.  (This is the same problem faced by the air-lines, the only realistic solution is 'hubs'.)
• If we define a 'currency unit', then we only require one exchange rate for each item - 10 items require 10 exchange rates (i.e. a price for each item).
• BUT: cacão beans deteriorate with time - I have seen them go mouldy in less than a year in a sealed container.  I would not like to see my peso currency notes or coins devalue over that sort of period.
• SO:  we cannot use cacão beans as currency - they devalue rapidly with time.  They can never be 'coins of the realm', issued and guaranteed by the 'state'.
• HOWEVER:  we can use cacão beans as a logical currency - 'this' of mine is worth 5 beans, 'that' of yours is worth 10 beans, so I must give you 2 of mine in exchange for 1 of yours.
• NOTE:  cacão beans themselves are also items for barter - they change hands.  If the bean was a logical 'coin', then exchanging beans for other items is no problem;  1 bean is worth 1 bean.  But if the bean is a 'real' coin, how (with what) do I buy cacão beans?  Do I give 25 cacão beans to pay for 25 cacão beans?  Suppose I don't have any cacão beans, and just want some?  I cannot 'buy' beans, I can only 'sell' something else.
• To work effectively and simply, a currency token must be something that is never bought or sold.  (except in a multi-currency world where I can barter pesos for dollars.)
• So I do not see people handing over cacão beans in payment for something, they are simply an invisible standard accepted by all as governing (standardizing) barter.
• So what are the 'bags under the table'?  Are they bags of beans to 'balance' up barters - a form of change?