Been getting a few questions about how often citric acid should be applied in the field. Curious what others have found to be most effective, but here's what we have found to be true (as a rule):
FIRST application: Mix 1 oz citric acid to about 1 qt water and spray all meat surfaces thouroughly. This mixture renders an acid wash of straight acid 1-2pH, but once applied the resulting pH is mixed with moisture inherent with the surface moisture (blood, water, vapor, etc). The final surface pH settles somewhere in the neighborhood of 3-4 pH after about 4-6 hours, initially. This acidity is highly effective at retarding initial bacterial growth and helps protect meat surface from initial bacterial invasion expected during the field process. CLEAN field care and handling of game meat is vital to the final taste and quality. Remember CLEAN, COOL, and DRY principles of preservation.
Once the meat is bagged, surface pH tests suggest acid levels continue to stabalize over the next 24 hours if no "new" water is allowed to contact the meat surface. It's vital to allow meat to continue cooling as quickly as possible during the first 12-24 hours to prevent deep tissue spoilage (bone sour) to occur.
After the first 24 hours, pH testing often suggests surface levels will balance out somewhere between 3.5-5 pH. This is a great start, since common spoilage bacteria is retarded with acid levels <5.5 pH. If hunters do not have pH test strips to perform frequent checks of surface acid levels, here's what they should do over the course of their field storage:
SECOND application: Our studies indicate that pH levels begin to rise to above 5 pH after the initial 24-hours post-application of the first wash, so occasional maintenance applications will be necessary to prevent future growth of spoilage bacteria on the surface of game meat. Our rule of thumb is to re-apply a new and complete citric acid wash every 2 days while the meat is stored in the field. This every-other-day application of citric acid will help ensure surface pH levels remain BELOW 5 pH.
AS NEEDED applications thereafter: If you have simple pH test strips in your kit, check surface levels in the wettest areas (around joints, between folds, etc.) every evening when performing normal sensory checks (smell, touch, visual). Cut away any suspicious meat (bloodshot, bruising, odd odors, foreign debris,etc.). Anytime surface testing reveals pH levels creeping toward 5 pH, reapply a new citric acid wash. Maintenance applications might be required more often on float trips (with wet or warm climates).
Without pH test strips, plan on a maintenance dose to be reapplied every 2 days until the game meat is transported safely from the field to its final point of processing. This will help safeguard your game without the threat of surface bacterial spoilage.
Along with CLEAN handling from start to finish, this is perhaps the best approach to properly handle edible meat in the field.