The mechanism of drip production: Formation of two compartments of extracellular space in muscle Post mortem

The structural changes occurring post mortem at 10°C in beef sternomandibularis muscle have been studied by fixing muscles at various times post mortem and examining transverse sections by light microscopy, or transversely cut surfaces by scanning electron microscopy. At 2 h post mortem, the muscle fibres filled the endomysial network and the fibre bundles filled the perimysial network. At 4 to 6 h post mortem, presumably as a result of fibre shrinkage, gaps appeared between the fibre bundles and the perimysial network but at this stage the fibres still filled the endomysial network. Gaps between fibres did not appear until about 24 to 48 h post mortem. It is concluded that at rigor onset, when myofibrils shrink owing to pH fall and the attachment of myosin heads to actin filaments, the fluid expelled accumulates in these two types of extracellular space. Such fluid, especially that accumulating between fibre bundles, is the likely source of drip.