How do I dip thee? Let me count the ways

AT the risk of being labelled a fusspot, I'll come right out and say it: I loathe double-dipping. I'm not referring to the accounting definition - where one draws an income from two different sources illicitly - although that's certainly bad too. I'm talking the boorish practice of dipping, say, a fry into a shared saucer of ketchup, taking a bite, and then immersing that half-chomped morsel into the sauce again.

Just typing this out, I can hear the splitting of factions - on the left, perpetrators who see nothing wrong with the habit, and on the right, my fellow comrades in arms.

Where you stand on the matter, I think, hinges on one single detail: whether or not you believe double-dipping is a food-safety issue. Do you think it could cause you to fall ill, because germs may be transmitted from a half-bitten chip to communal salsa dip? Or are you someone who thinks that's a load of baloney?

As it turns out, science has the answer. Late last year, an undergraduate team of researchers at Clemson University designed a series of experiments to see if there is indeed bacterial transfer during the double-dipping process - and if so, to what degree.

To start off, the researchers compared two glasses of water - one with a bitten cracker dipped in, and another with an unbitten cracker dipped in. Their findings shouldn't come as a surprise: they found about 1,000 more bacteria per millilitre of water in the cup adulterated by a bitten cracker, compared to the other.

The researchers then did the same test on actual food dips: salsa, chocolate, and cheese. This time, they measured bacterial populations not only right after the crackers had been dipped in, but also two hours after.

Wrote Paul Dawson, Professor of Food Science at Clemson University and leader of the study: "We found that in the absence of double-dipping, our foods had no detectable bacteria present. Once subjected to double-dipping, the salsa took on about five times more bacteria (1,000 bacteria/ml of dip) from the bitten chip, when compared to chocolate and cheese dips (150-200 bacteria/ml of dip)."

This massive difference in bacterial transfer was due to varying levels of viscosity. While chocolate and cheese are pretty thick, salsa is of a far thinner consistency - meaning there's a higher chance that contaminated morsels are falling back into the shared dip. Prof Dawson adds: "The lower viscosity (of salsa) means that more of the dip touching the bitten cracker falls back into the dipping bowl rather than sticking to the cracker. And as it drops back into the communal container, it brings with it bacteria from the mouth of the double-dipper."

Ugh.

Interestingly, acidity levels made a difference, too. Two hours after the double-dipping offence, researchers found that the salsa bacterial numbers had dropped to about the same levels as those seen in the chocolate and cheese, since some of the bacteria had been killed by the salsa's acidity.

So we now know that double-dipping can indeed transfer bacteria from mouth to dip. And while that's gross, does it necessarily mean we should be concerned? After all, over 700 different strains of bacteria have been detected in the human mouth, with most of them being harmless. Some, in fact, are even beneficial; they may aid in the digestion of food.

But when it comes to actual illnesses that can be spread through saliva - such as the flu virus or severe acute respiratory syndrome (SARS) - it's hard to deny that double-dipping is a food safety problem. Even if some cold and flu viruses don't live outside the body for long, there's still a reason the Health Promotion Board recommends covering your mouth and nose with a tissue when you cough or sneeze; this prevents the release of respiratory droplets into the air.

So - surprise, surprise - science says don't double-dip. But what's a sauce-loving person to do, to ensure that every fry bite has some ketchup on it? The most civilised option is probably to scoop out what you need with a serving spoon, put that on your plate, and enjoy it to your heart's content.

But what if that's not an option, and you're hell-bent on partaking in the communal dip? I propose three killer single-dipping moves:

Bon appetit!