Making leather used to be a smelly business. First, you soaked animal hides in a mixture of urine and lime to remove hairs, flesh, and fat. Then, you softened the skins by kneading them in dung from dogs or pigeons. This took 2-3 hours and was usually done with your bare feet. No wonder leather making was considered a noxious trade relegated to the outskirts of town.

Enter the enzymes

The leather industry moved away from these foul practices in the beginning of the 20th century. The scientist Otto Röhm discovered that it was an enzyme in the dung called trypsin that did the work. He managed to extract the enzyme from pig pancreas and started a company to sell it. It revolutionized the industry.

Since then, other enzymes have gradually been introduced in leather making. Today, most of the enzymes come from microorganisms such as bacteria and fungi. Companies like Novozymes ferment the microorganisms in large steel tanks and harvest the enzymes they produce.

These enzymes have not only replaced animal feces. They have also reduced the use of toxic chemicals in the leather industry and shortened process time. The wastewater is cleaner. Working conditions have improved.

Less chemicals, water, energy, and CO2

A new study shows the benefits of replacing chemicals with biotechnology. The study, published in International Leather Maker, compares the conventional chemical process of soaking, liming, and unhairing of calfskins with a new enzyme system that loosens the hair roots and removes the hair on the hides.

The enzymes cut use of sodium sulfide, a toxic chemical used to ‘burn’ hair from the hides, by 60 percent. They reduce water use in soaking and unhairing by one-quarter, and the toxicity of the effluent is greatly reduced. The process reduces energy use and greenhouse gas emissions by almost 30 percent.

And since the hairs are removed rather than burnt with chemicals, they could be used to make biogas. Maybe the leather makers of yore were more advanced than we think when they looked to nature for solutions?

Though they would probably have preferred odorless enzymes to dung.

What is tanning?

Tanning is the process of treating skins and hides of animals to produce leather. It is essentially a way to mummify a hide so it will not rot or harden.

The beam house step of the process is where the raw hides are soaked and hair removed, and chemicals added to prevent the hides from decomposing.

Wastewater from the process may be contaminated with chemicals such as lime, sulfides and acids, as well as chromium, which can pose risks to the environment and human health.

The leather industry has come a long way in applying new technologies to reduce pollution. Treating leather with enzymes shortens processing time and reduces the use of water, energy and chemicals. It also improves the quality of the leather.

Around 7 million tons of bovine hides are processed every year. Most leather is used to make shoes, while the second largest category is goods such as gloves, bags and belts. Leather clothing, auto upholstery, home furnishings, and miscellaneous other uses make up the remainder.