vi: The Chemistry Column
Fresh fingertips Claire Gormley If you love to cook, you’re probably familiar with the dreaded ‘Garlic fingers’— that smell that can linger long after you’ve prepared your food, eaten and cleaned-up. In my house I'm strictly on dishwasher duty, so I was sceptical when my partner insisted that rubbing your fingers with stainless steel after handling Garlic (Allium sativum) removes the odours. It seemed too much like an old wives’ tale, and the ‘steel soap’ products on the market just made me chuckle (particularly the Garlic-shaped one!). Unsurprisingly, the removal of Garlic odours from fingers using stainless steel has not been at the top of researchers’ lists of most important topics to study— studies tend to focus rather on Garlic’s anti-bacterial properties and its potential as a therapeutic — so I only found reports such as those in NPR and Scientific American, detailing at-home experiments, with variable results (Leontiev et al, 2018; Li et al, 2015). I was ready to stop my investigation when I came across a short (2019) blog written by Dr. Anne Marie Helmenstine —a former college professor now working as a science writer and consultant— describing how the sulfur compounds in Garlic and Onions form metallic bonds with the various metals in stainless steel.
The science goes like this: When we slice up Garlic or Onions a volatile gas, propanethial S-oxide, is released into the air around us. Upon contact with water, this gas reacts and forms sulfuric acid— that’s the compound that makes our eyes water and sting (Helmenstine, 2019). The sulfur contained in both of these elements is relatively electronegative, meaning it has a strong attraction to electrons. Due to sulfur’s attraction for electrons, it will form bonds with many other elements in order to “share” their electrons— or in the case of ionic bonds with metal elements, take the metal’s electrons completely —to become more stable. The mechanism by which sulfur compounds bind to metals is quite complex and varies depending on the type of metal present. In the case of sulfur compounds binding to steel, there are multiple metals to consider. It is thought, however, that as we rub our Garlic-y fingers against a piece of stainless steel the odour-causing sulfuric compounds on our fingers bind with the metal atoms in the stainless steel, thus removing the odour from our hands. However, the reaction takes time to complete, and will be dependent on how many sulfuric compounds are on one’s fingers— which may be why so many kitchen scientists still smell Garlic on their fingers after trying this trick… 33
