What are the sights, the sounds, the smells, and the textures that you associate with Christmas? Perhaps it is Christmas trees with their lovely green shape, color and wonderful pine smell. Maybe it’s the smells of cooking, the savory smells of turkey or the sweet smell of warm cookies. Or what about all of the cozy feelings you get with big sweaters or a roaring fire? Did you know that there is a lot of chemistry that goes into all of the senses we associate with this holiday?
I was browsing through holiday-related articles, looking for something different from the usual psychology or sociology centered holiday study. That’s when I came across an article from 2012 published in the Journal of Chemical Education about the five senses of Christmas chemistry. The authors look through the lens of organic chemistry and take five “Christmas compounds” to examine in the context of the five senses.
Sound: Silver Fulminate
Christmas crackers are items that are a more traditional favorite in the UK. The Christmas crackers used today are short cardboard tubes wrapped in colorful paper. When they are pulled – bang! – out comes a colorful hat (usually looking like a crown), a small toy or a joke. The sound is made from the rapid breakdown of silver fulminate present in small quantities in the paper. Two thin strips of cardboard are glued together, one containing silver fulminate and the other a rough surface. When the cracker is pulled, the surfaces rub together to produce friction and facilitate the reaction. The compound goes through a redox reaction followed by a release of nitrogen gas and carbon monoxide. This sudden production of gases is what produces the distinctive popping sounds.
Touch: Sodium Acetate
Many hand warmers are based on a simple chemical reaction – the crystallization of a supersaturated sodium acetate solution. When you squish around the contents of the hand warmer, you are triggering a chemical process. A nucleation site, usually a metal disk with small seed crystals, causes rapid crystallization of the super saturated solution. This is a highly exothermic process that releases energy to its surroundings as heat. These types of hand warmers are often reusable because of their physical mode of action. Other hand warmers rely on the exothermic oxidation of iron when exposed to air. Activated charcoal is used to catalyze the reaction, along with vermiculite and salt as additives. However, this chemical mode of action means that these are one use only products.
Tryptophan is an essential aromatic amino acid that is commonly found in proteins. This compound has two enantiomers, chiral molecules that are mirror images of one another (kinda like left and right hands). L-tryptophan exists in nature and has a pronounced bitter taste, while D-tryptophan is synthetic and has a very sweet taste. Once you consume tryptophan, it goes through a series of metabolic reactions, one of which ends with melatonin. This final product is a neurohormone that is naturally secreted by the pineal gland, is involved in regulating circadian rhythms and may also have strong antioxidant effects.
Considering this chemistry, you can alter the flavor of the ginger you use in your cooking. For example, if you cook ginger extensively, particularly in the absence of acid, then you produce the mildest tasting vanilloids, zingerone. But also keep in mind that your kitchen conditions are not laboratory conditions. This means that you are likely to end up with a mixture of all three compounds in your cookies.
That’s all for our journey through the senses of Christmas. If you are a chemistry teacher, or simply a chemistry nut, then I recommend reading through the paper. It has all sorts of skeletal formulas that you’ll love.
Jackson, D., & Dicks, A. (2012). The Five Senses of Christmas Chemistry Journal of Chemical Education, 89 (10), 1267-1273 DOI: 10.1021/ed300231z
p.s. In the interest of equal opportunity holiday science, does anyone recommend a study on Hanukka, Kwanzaa, etc. My academic database search is coming up with nil.
(images via Science Notes, Old English Crackers, Buzzle, ThinkGeek, NYTimes Blogs, spydersen, respectively)