Periodically turning the pile, tearing it apart with a fork and restacking it, will reestablish a looser texture and temporarily recharge the pore spaces with fresh air.  Since the outer surfaces of a compost pile do not get hot, tend to completely dry out, and fail to decompose, turning the pile also rotates the unrotted skin to the core and then insulates it with more-decomposed material taken from the center of the original pile.  A heap that has cooled because it has gone anaerobic can be quickly remedied by turning.

Piles can also be constructed with a base layer of fine sticks, smaller tree prunings, and dry brushy material.  This porous base tends to enhance the inflow of air from beneath the pile.  One powerful aeration technique is to build the pile atop a low platform made of slats or strong hardware cloth.

Larger piles can have air channels built into them much as light wells and courtyards illuminate inner rooms of tall buildings.  As the pile is being constructed, vertical heavy wooden fence posts, 4 x 4’s, or large-diameter plastic pipes with numerous quarter-inch holes drilled in them are spaced every three or four feet.  Once the pile has been formed and begins to heat, the wooden posts are wiggled around and then lifted out, making a slightly conical airway from top to bottom.  Perforated plastic vent pipes can be left in the heap.  With the help of these airways, no part of the pile is more than a couple of feet from oxygen

Moisture. A dry pile is a cold pile.  Microorganisms live in thin films of water that adhere to organic matter whereas fungi only grow in humid conditions; if the pile becomes dry, both bacteria and fungi die off.  The upwelling of heated air exiting the pile tends to rapidly dehydrate the compost heap.  It usually is necessary to periodically add water to a hot working heap.  Unfortunately, remoistening a pile is not always simple.  The nature of the materials tends to cause water to be shed and run off much like a thatched roof protects a cottage.

Since piles tend to compact and dry out at the same time, when they are turned they can simultaneously be rehydrated.  When I fork over a heap I take brief breaks and spray water over the new pile, layer by layer.  Two or three such turnings and waterings will result in finished compost.

The other extreme can also be an obstacle to efficient composting.  Making a pile too wet can encourage soft materials to lose all mechanical strength, the pile immediately slumps into a chilled, airless mass.  Having large quantities of water pass through a pile can also leach out vital nutrients that feed organisms of decomposition and later on, feed the garden itself.  I cover my heaps with old plastic sheeting from November through March to protect them from Oregon’s rainy winter climate.