Here is my current view of the process of reed aging, drawing on this dissertation, other sources, and my own experience:
1) As shipped from the factory, a commercial reed is a dried shell of what was once a living cane plant (Arundo donax). When it is first played, the reed’s cells absorb water, becoming “hydrated.” Elasticity increases, and the reed begins to play more easily.
2) The introduction of moisture then leads to the beginning of our problems: The reed swells up, and not in a predictable or uniform way, since each piece of cane has a different structure. The reed acquires warps, and may play with more difficulty. Once this deformation takes place, the reed will not return to its original state, even after drying.
Generally, the thicker part of the vamp swells the most. Note that this is the part that sits below the “window” of the mouthpiece as the instrument is being played, and is therefore exposed to quite a bit of moisture.
Here is where the art of reed adjustment would come in.
Very few clarinet and saxophone players keep reeds permanently wet, or allow them to become fully hydrated (soaked). Generally, we just dampen them to some degree. This means that swelling will happen gradually, over a number of playing sessions. Thus, many players will make gradual adjustments (using a reed knife, sandpaper, clipper, etc.), over several playing sessions, to stabilize the reed.
Excessive hydration has a negative effect. You may have noticed that after an hour or so of continuous playing, a reed will begin to play “softer,” losing crispness of attack and projection, due to excessive saturation with saliva. The next day, that same reed might play well again, after drying somewhat.
However, reeds must be at least partially hydrated to respond well - hence the use of humidifiers (commercially available, or just a piece of orange peel in the box). Playing on a reed a little each day will also maintain humidity, unless the weather is particularly dry.
3) Over time, as it is played, the reed’s ability to absorb water decreases, and the reed’s shape stabilizes. According to Casadonte, this is because hemicellulose, a major component of reed cell walls that aids in the absorption of water, is degraded as the reed is played.
A new reed will often have a “sweet” taste; Casadonte speculates that this is due to the presence of AMDX, the primary hemicellulose in reeds. This taste goes away as the reed is broken in, and the AMDX breaks down.
4) As the reed ages, its surface becomes coated with deposits of matter (calcium, etc.) from evaporated saliva, further preventing the reed from absorbing water, reducing its resiliency. In addition, saliva contains ammonia and other alkali, which cause the cane to become “softer.”
Bacteria also begin to colonize the reed surface (mostly Staphylococcus epidermidis, a harmless and normal part of human skin flora).
Besides impeding the absorption of moisture, these substances add mass to the reed tip, causing further loss of resiliency.
An anecdote: Over the years, I noticed that some students’ reeds had some kind of black growth on them. One day I mentioned this to an adult student, Alan G., a dermatologist. Alan said, “Aspergillus niger.” He explained to me that this a fungus that lives in soil, and in the environment. Some individuals harbor it naturally, and harmlessly, in their mouth. This proclivity is an inherited trait. That cleared up one reed mystery! This problem can be minimized by keeping reeds clean, rinsing and drying them after playing.
For all of us, bacteria growth and saliva deposits can be minimized by hydrating the reed with tap water when possible before playing, and by keeping the reed clean and relatively dry between sessions. Occasionally, you might want to lightly scrape "crud" off the surface with a thumbnail or with a reed knife. In the later stage of a reed's life, it can be somewhat rejuvenated by briefly soaking it in a hydrogen peroxide/water solution, and then rinsing and drying - but this is a very temporary fix.
By the way, Casadonte notes that since inability to absorb water is a cause of reed deterioration, “sealing” reeds (by rubbing, or waxing) may not be a good idea. Of course, many experienced players would disagree (personally, I don't seal my reeds).
This reminds me of a practice used over the years by some players: moistening reeds with vodka or gin, sometimes mixed with water, and sometimes even leaving the reeds permanently wet, stored in an alcohol/water mixture. This and other reed preservation issues are discussed in this interesting forum thread, which includes posts from Casadonte and from a contributor who worked at Rico Reeds for 15 years.
5) As the reed is played, it will gradually develop a bend towards the mouthpiece facing. At the beginning this might be a good thing, improving the seal between reed and facing. But over time, the tip opening will become more closed, and the reed will respond poorly. Sometimes a little more life can be coaxed out of the reed by inserting a business card (or other flat piece of cardboard or plastic) between the reed and the mouthpiece facing, and bending the reed slightly upwards, away from the mouthpiece, for 10-20 seconds or so. However, this also is a very temporary fix.
All reeds will eventually wear out, due to the factors described here. But reed life can be prolonged, and their “quality of life” improved, by hydrating with water rather than saliva, by adjusting, and by keeping them clean.
If you would like to order a copy of the dissertation by Donald Casadonte, you can do so at proquest.com.
Here is a link to the James Kopp article mentioned at the start of this post - addressed to bassoonists, but with information that applies to all reed players.
Finally, here is an article of mine, surveying several books about single-reed adjustment.
