A preserved hammerhead shark in alcohol in Berlin's East Wing of The Natural History Museum. (Image credit to Sean Gallup/Getty Images).
If you have ever been to a museum or laboratory and seen a perfectly preserved eyeball or tiny dead creature floating in a glass container, then you have experienced the preservation power that alcohol has. Fluid preservation is the formal name for this method. Since the 1600s, scientists have relied on fluid preservation to preserve their specimens. According to the American Museum of Natural History, it can be used to preserve a specimen for hundreds of years if it is done properly.
But how does it all work?
Live Science was told by Bill Carroll, adjunct professor of Chemistry at Indiana University Bloomington. He gave wine as an example. It is made when yeast consumes sugar from grapes, then excretes alcohol. He said that yeast can excrete so much alcohol, it becomes toxic and kills yeast. According to the California Wine Advisor, an alcohol content of around 14% can delay the growth and death of bacteria for many years. Many wines also contain additional preservatives such as sulfur.
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Katherine Maslenikov from the Burke Museum in Seattle, who manages the fish collections, stated that preservation of other organic material like DNA, tissues, or entire animals requires a higher alcohol content. Maslenikov primarily uses alcohol for long-term storage, particularly ethanol.
Maslenikov may take a specimen of fish, extract some tissue samples to do DNA analysis, and inject formalin into the fish. This will stop internal biological processes such as enzyme reactions and tissue destruction. Maslenikov might then immerse the specimen in 70% alcohol and 30% water. Maslenikov stated that 70% alcohol is the ideal amount for long-term storage. She said that there is enough water in the solution to keep the tissue hydrated. This helps the specimen or animal retain its shape. There is also enough alcohol to stop mold growth.
Higher concentrations of alcohol, such as 95% ethanol, work as dehydrants. This means that it replaces water in cells, tissues, and whole-body specimens with alcohol. According to Arkansas State University's Ask a Biologist series, the lack of water can cause changes in water-sensitive proteins. They unfold or denature and then harden together, fixing the specimens' shape. According to a study published in 2013 in PLOS One, this technique is common for preserving DNA.
It can be difficult to decide how much alcohol to use. Too much or too little alcohol can alter the shape and flexibility of the sample, as well as reduce its ability to retain the solution. The specimen will be preserved if it is dehydrated at high levels of alcohol. Maslenikov stated that this process can cause a specimen to become brittle and shriveled due to the loss of water. It's okay to lose some water, but it depends on the item you want to preserve.
If a specimen is left unattended, it can quickly become brittle.
Christopher Rogers, associate research professor at Kansas Biological Survey, Center for Ecological Research, at the University of Kansas, stated in an email that "if an organism has enough moisture in its tissues, it will dilute the alcohol." This could mean that the alcohol concentration may not be strong enough to kill any microorganisms hidden in the specimen. The specimen can be decomposed by the bacteria that was not found. Rogers stated that it is crucial to alter the alcohol within 24 hours of picking the critter. This increases the solution's alcohol content.
Carrol stated that alcohol can be used as a preservative.
Original publication on Live Science
