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Curing
The curing of meat products is one of the most important meat technology processes and its purpose is to develop boil-proof colour, to preserve the meat (selective inhibition of micro-organisms) and to form the typical cured flavour.
Saltpetre (as sodium or potassium nitrate) or nitrite curing salt (i.e. a homogeneous mixture of table salt and a maximum of 0.6% sodium or potassium nitrite) are used as curing substances. These are broken down in several steps to nitrogen oxide, which is bound to the muscle pigment myoglobin (either to reduced myoglobin or to metmyoglobin). Legally prescribed limits for the nitrate or nitrite content refer mainly to the residual content in the product (cf. Additives Ordinance, Annex 7D, point 4.2).
- Nitrate is primarily used for curing longer-aged raw sausages and raw cured products. It is converted to nitrite by bacterial nitrate reduction (originating from micrococcaceae) with fairly high pH-values and then transformed through acid-dependent processes to nitrogen oxide and nitrate. Bacterial conversion itself is a tricky phase during curing and if excessive amounts are added or production conditions are less than optimal, this can lead to greatly increased nitrate levels in the end product due to insufficient development of the bacteria which create nitrate reduction. Care should also be taken that the first phase of the curing of longer-aged raw sausages and raw cured products is to a very high standard especially due to the high water activity values (aw) and pH-values in the raw materials. Conversely, nitrate has the effect of delaying the bacterial reduction to nitrite when the correct environmental conditions are maintained so that higher nitrite concentrations in all phases of production can be prevented. This may be important mainly in connection with the recently noted prooxidative effect of the nitrite in that this seems to allow fat oxidation to speed up.
- Nitrite in the form of nitrite curing salt is primarily used for curing short-aged raw sausages, cooked sausages (without white sausages), sausages from cooked meat, cooked cured products and other meat products, also in combination with glucono-delta-lactone (GdL) depending on the product. The chemical breakdown of nitrite to nitrogen oxide takes place at a low pH by means of nitrous acid.
A distinction is made in curing between dry and wet curing:
- Dry curing consists of rubbing the pieces of meat by hand with a mixture of table salt, saltpetre or nitrite curing salt and a proprietary mixture of herbs and spices. During subsequent storage for several weeks at 5°C in trays or racks, its own brine is formed. The pieces of meat must be regularly turned for even curing.
- In the case of wet curing, a 10 to 20% curing brine (table salt, saltpetre or nitrite curing salt, proprietary mixture of herbs and spices) is added to the piece of meat. This is carried out either by laying the pieces of meat in racks or trays in a brine at around 5°C (brine curing: e.g. in the case of “Kochspeck, Gnagi”, tongue) or by injecting the curing brine into the piece of meat with needles, automatically or by hand (injection curing: e.g. in the case of boiled ham, “Rippli”).
Curing is occasionally called into question due to the possible formation of nitrosamines, which can have a carcinogenic effect. More recent investigations indicate that between 3 and 10% of nitrosamines occurring in the body originate from food and the rest are formed in the body. The addition of ascorbic acid/ascorbate can prevent the formation of new nitrosamines, but also seems to reduce their breakdown in the body.
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