Professor Rot says:
This is my Famous Lecture #2,432.
It's all about those crazy little microbes who just love the heck out of your compost pile.
Feed them well and they will giddily eat themselves to death! Yahoozy!
The type of composting you are likely to be doing at home is called aerobic because it combines the advantages of air, moisture, and heat to decompose organic matter. By contrast, anaerobic composting is like sealing your organic matter in a container without air. As a result, the material never heats up, although it eventually decomposes over a lengthy time period.
Note: when you stockpile food scraps in a bucket with a secure lid (4-5 gallon in size) to later add to your pile, the scraps essentially start decomposing in the anaerobic fashion; this is why the scraps start looking mushy and liquify. See Stockpiling and Food Scraps for further tips.
In your regular compost pile are billions of microbes, mostly bacteria, who love the conditions of air, moisture and heat. They eat, grow, reproduce, and die with almost giddy intent. They are the ones responsible for the rise and fall of temperature in your pile.
Let's meet some of the workers from this bacteria union who are more than happy to work in "thermo shifts" according to the temperature in your bin. Their uniqueness is worth the scientific education, so below you will learn about them in general and in what way they populate your compost pile.
Below 55°F/13°C: Most microbes in your compost pile are semi-dormant with little breakdown.
At 14°-68°F/13-21°C: PSYCHROPHILES
A psychrophile (also known as a cryophile) is an organism that reproduces and grows best at low temperatures, typically in the range -10 to 20°C (14 to 68°F). Psychrophiles are a type of extremophile. Some have been found to thrive in the Arctic and Antarctic oceans, which remain frozen for much of the year. Others have been recovered from core samples taken from the Greenland ice sheet at depths of about 3 kilometers. Psychrophiles possess enzymes that are adapted to function at low temperatures and are denatured at moderate temperatures. They also exhibit polyunsaturated fatty acids in their lipids.
What Happens in Your Compost Pile
These cool-temperature bacteria invade the pile and begin to burn or oxidize carbon, releasing heat and nutrients in the form of amino acids. Even though psychrophiles are present in your pile below 55°F/13°C, you may not necessarily notice heat or breakdown in the pile. This is why compost piles are somewhat "dormant" in late Fall to early Spring. To give your pile a boost in the Spring use an activator such as QR Compost Activator (sold on this website) or other types of activators as described in Compost Activators.
As the temperature rises in your compost pile, the next crew of bacteria arrives: the mesophiles.
At 70°-90°F/21-32°C: MESOPHILES
Most of the microorganisms on earth belong to the group of mesophiles. Mesophiles grow best in temperatures between 10-50°C (50-122°F). They are found in soil and water environments. Most of the diseases, caused by bacteria and viruses, that affect humans come from the mesophile group. Some of the most dangerous mesophiles are Staphyloccus aureus, Salmonella sp. (image to the left), Proteus vulgaris, and Yersinia enterocoiytica.
How are mesophiles identified?
Mesophiles are identified by several characteristics. Where they live is one way because of the temperature that they need to grow in. Another way is that they can spoil food and dead animal matter quickly. Yersinia enterocoiytica is the mesphile that contaminates blood stored in bags for patients that need transfusions. E-coli bacteria (image to the right) are mesophiles that cause vicitims to bleed or hemorrhage. E-coli can cause death in humans.
If the temperature is just right, mesophiles can double their population in just 30 minutes. Mesophiles reproduce through mitosis, cell division, or by sexual reproduction with a male or female bacteria.
What Happens in Your Compost Pile
Mesophiles are one of the microorganisms that can cause food to spoil quickly. They love food scraps, whether its leftovers in the refrgerator or waste in your compost pile. They are also important to the process of composting any type of organic matter. In a compost pile the microorganisms that make the matter break down take turns working. When new compost material is added to the pile, the temperature is cool enough for mesophiles to work, so they take charge. When the matter is broken down the pile becomes too hot for the mesophiles, then the thermophiles take over.
In a nutshell, mesophiles are the real workhorses of the compost pile. For that matter, they're the primary sanitation crew for all of Mother Nature! In the confines of your compost bin they consume literally everything in sight, generating enough heat to raise the temperature to over 100°F/38°C. In a Batch Pile, the mesophiles work quickly. In the Add-as-You-Go Pile, they pretty much do most of the work because the pile never gets hot enough for those crazy lunatic heat-loving thermophiles to take over.
In a compost pile destined to go out in a blaze of glory, the demise of the mesophiles eventually sets the stage for thermophilic composting.
At 90°-200°F/32-93°C: THERMOPHILES
Thermophiles are microorganisms that live and grow in extremely hot environments that would kill most other microorganisms. Thermophiles are grouped into either prokaryotes or eukaryotes, and these two groups of extremophiles are classified in the group of archaea. They grow best in temperatures that are between 90-200°F/32-93°C. They will not grow if the temperature reaches 68°F/20°C. Thermophiles are not easy to study because the extreme conditions that they need to survive are hard to provide in a laboratory.
Thermophiles either live in geothermal habitats (like geysers, hot springs, molten material), or they live in environments that create heat themselves. A pile of compost and garbage landfills are two examples of environments that produce heat on their own.
What Happens in Your Compost Pile
At high temperatures, thermophiles arrive to do the "hot" composting. They work efficiently, devoting their 3-5 day life span to raising the temperature high enough, hopefully, to destroy any sneaky desease germs or weed seeds. High temperatures also generate humic acid, which enables plants to assimilate the nutrients in the compost.
High temperatures are easier to accomplish in a Batch Pile than a Add-as-You-Go Pile. Why? Because the Batch Pile is created all at once to ensure a large enough volume to heat up. Of course, there must be a good balance of ingredients (see The Carbon/Nitrogen Ratio), moisture, air, and possibly an activator to spark heat in the pile. Finally, Turning Your Compost, at least in the first 2-3 weeks, aids in reheating the pile.
Above 140°/60°C: The pile stabalizes in this range for a few days
NOTE: If you turn your pile just as the temperature is beginning to drop (see Turning Your Compost), you will create more air flow and cause the pile to heat back up again. Yippee! This will allow those noble thermophiles to receive over-time pay before retiring. Remember, more heat means better and faster compost.
Now the pile will gradually decrease in temperature until the mesophiles and psychrophiles move back in from the cooler edges to resume their activity. Other hungry guests will arrive as well in the form of actinomycetes, fungi, worms, and many insects. What a party! (If you only knew half of what was going on out there!)
No WORMS in Your Bin?
No Problem! Most people think that a compost pile should have worms in it. Not necessarily so. If your bin sits on soil, worms may rise up naturally out of the earth beneath the bin later in the decomposing process when the heat is lower. They have tender feet.
However, no worms is not a sign that you have failed in your efforts. Put your compost in your garden beds and the little cuties will love you immensely. That's where they really hang out!
Learn more about vermicomposting: Worm Composting
"When Can I Expect Finished Compost?"
You mean how long does all this eating and digesting and partying take place in your compost pile?
Expect usable compost in as little as 3-4 weeks, if you build a Batch Pile and do everything perfectly. But it could take as long as 8-12 months if you use the Add-as-You-Go composting method.
How motivated are you? End of lecture, class dismissed.