Leatherwork has always been an enjoyable craft for me, I don’t consider it a business. For one, it’s an honorable and enjoyable way to make my keep. It’s also a wonderful way to meditate, as more often than not I find inspiration in the actual work itself. Once I’m done with class and homework, my nightly ritual is to pour a nice glass of wine, put on a record and set to work on whatever may be on my workbench. I spend time researching good wine just as I spend time looking for the perfect pair of boots, a great eco friendly tote bag for post office trips, or a nice new awl. They are both passions, and when I found out they were so closely linked, I had to share (I’m sure there are readers that are just as interested in this as I am).
I started by researching the vegetable tanning process for a chemistry project. In theory, leather had never made sense to me. Unprocessed animal hide is soft, floppy, and decomposes quickly, where as leather has strength, body, and can withstand some of the harshest conditions on earth. Leather, unlike some of the more modern technologies in fashion, has also been around for hundreds and thousands of years…so this couldn’t be complicated technology. It must be something simple.
The tanning process is old, and refers to the chemical treatment of animal hides to produce leather (not tanning in the sun). All hides are dried and cured with salt, then soaked in clear water to be desalted. Once the hides are clean, they are soaked in milk of lime, which loosens and removes hair and grease, and begins the process of conditioning the collagen for tanning. The rest of the hair is then removed using a machine and a process called scudding, which is the manual removal of hair with a dull or plastic blade.
The next few steps chemically prepare the hide for tanning. First, the pH level of the collagen (hide) are lowered by bathing the hide in a vat of acid in a process called deliming. Deliming allows the hide to be treated with enzymes in a process called bating, which smoothes the grain of the leather and softens it. Without lowering the pH level, the enzymes would have no effect on the hide. This is the last step before actually tanning.
The Vegetable Tanning process then starts with a substance called Tannin, which is an organic substance found in plants- mostly in bark, leaves, and the immature fruit of plant life. Tannins are astringent. This means they tend to constrict and shrink body tissue. It also means they taste bitter. Tannin can be made from many different plants, but historically, back to the 19th century, only three types of bark were used- sumac bark, oak bark, and hemlock bark.
Making Tannin is much like making tea. Ground up bark is simply soaked in hot water for two days. At the end of these two days, the tannic acid created is put through a number of vats, and manipulated until the desired strength is reached.
As a note to the environmentally conscious: at the end of the 19th century, many tanneries had installed furnaces to burn the bark either wet or dry after it had been used to make tannic acid. This made use of the waste by heating the water and tannery itself in the winter months.
The hides are stretched out on frames and exposed to Tannin in varying strengths for varying amounts of time. Once the process of vegetable tanning is complete…we’ve got leather. So how, chemically, does this process create leather? Tannins are defined by their chemical function. They are “polyphenolic compounds that bind to and precipitate proteins”. In more simple terms this means that Tannin is chemically able to link and bond with other chemicals. It solidifies the proteins in the hide and turns the skin into a firm and tough piece of leather that won’t decompose.
Tannin serves a different, but just as important, purpose in wine making. First of all, the tannins used in wine come mostly from grapes: their sin, seeds, and stems. They also may come from the wooden barrel used to store the wine if it’s new. Wine tannin is changed in the fermenting and storage process, thus wine tannin is chemically more complex than grape tannin. During this process, grape tannin is condensed through polymerzation, where a polymer called proanthocyanidin is created. This bond is hard to study, because it is constantly breaking and reforming in a varying lengths of sequence.
So far, research has concluded that tannins contribute at least two things to the actual taste of wine: bitterness and astringency. The difference between the two is that bitterness is a taste, one of the five main tastes that we have (the other four being salty, sweet, sour, and umami). Asringency, while very similar to bitterness, is actually thought to be a chemical reaction between the tannins and our saliva. Like in leather tanning, it is thought that tannins bond with proteins in our saliva to precipitate them out, causing friction between the surfaces of the pallet. This is the feeling of “dryness” we get when drinking wine.
I think it is only fitting that these two things relate in the end. Objectively, they are both organic processes that change one compound to another through bonds using the proteins of living or once living animals. However, subjectively (for me at least), they link two things which I’m passionate about, and allow me to enjoy my work just that much more. The research of wine is still in it’s infant stages as well, so who knows what else will be found. I’ll make sure to keep everyone updated!