In the main, our individual calculations have produced similar or the same results and in general we agree the likely implications of these results. I will highlight any areas where we are not in full agreement.
NCPaul tested a 1.2 kg piece of pork in a 2:1 Meat:Brine ratio immersion cure over a period of 11 days. He analysed the salt level of brine daily to monitor the progress of the cure into the meat. The water content of the brine was tested at days 4 and 11. The salt level of the meat was tested at the start of curing and on day 11 when the meat was tested in two places, the centre and the outer portion.
Our calculations have looked at the brine and meat as a single system as in Method 2 on page 22 of the United States Department of Agriculture Food Safety Inspection Service Processing Inspectors’ Calculations Handbook (Page 27 of the .pdf document). We have taken the natural salt into account in our calculations and believe that:
- Full equilibrium is unlikely to be reached in less than about 19 days per kg of meat.
- Cure enters the meat very quickly in the initial stages: very slowly in later stages.
- The outcome of immersion cures cannot be calculated from the final equilibrium levels on a strictly pro-rata basis – half the time does not equal half the curing.
- Although the salt enters the meat quickly it takes a long time to reach the centre portion.
- The movement of water/liquid between brine and meat is likely to based on difference between the respective levels of water in the brine and the natural water in the meat. Where the brine has a higher water level than the meat we believe that the primary movement of water will be ‘in to’ rather than ‘out of’ the meat.
- The safest time per kg for cures is 10 days. Below this the higher daily changes make accurate curing unpredictable.
- Irrespective of the amount of brine the meat will only naturally pick up 8 – 10% of the brine ingredients naturally and that Method 2 calculations for these brines will not give an accurate reflection of the levels of cure in the meat unless this is taken into account in the calculations.
From these observations and their associated calculations we believe that curing meat for 10 days per kg in a 2:1 Meat:Brine ratio cure calculated at 85% of equilibrium is the safest option. In calculating immersion cures to Method 2 an additional 17.5% should be added to the desired levels of salt/sugar/curing salt at equilibrium to achieve this. For a cure compliant with the European Union’s 150 PPM nitrite level it should be calculated to 175 PPM. The US level of 200 PPM should be sufficient to still be used and remain safe.
Jim believes that this is good for all sizes of meat. Whilst I agree with him in principle, I am not prepared to commit to this for larger pieces of meat, whole hams etc, on the basis of a test on one smaller piece of meat, although I believe that he is probably correct.
The 10 day per kg curing period should be followed by an equalisation period to allow the cure ingredients to spread evenly throughout the meat. Within reason this should be lengthy probably a minimum of 5 days per kg – however we have no tests to show the movement after curing so these are our thoughts based solely on the movement during the curing period – they may be different post cure.
Both of us would like to thank Paul for the great work he did testing this meat.
Jim and Phil
