Ageing of Beef PrimeSafe Technical Guideline

Dry ageing involves the degradation of connective tissue and muscle protein structure of the meat of carcasses or cuts of meat and must be managed to ensure growth of beneficial and non-harmful moulds. Best practice is to reduce carcasses to smaller primals and sub-primals in preparation for the ageing process. The most popular cuts used for ageing are strip loin, rib eye and sirloin that can be aged in dedicated refrigeration units or rooms. For dry aged meat, the fat cap is often left on the meat to help with flavour development, retention of moisture and reduction of trim loss when the crust is eventually trimmed off.

Dry aged beef has an intense flavour when compared to wet aged meat that can have a sour blood/serum flavour. The reason for this is that the predominant bacteria on dry aged meat are the Pseudomonas that grow in the presence of oxygen. This is different to wet aged packaged meat where Lactobacilli bacteria grow in the absence of oxygen. The Lactobacilli bacteria convert lactose to lactic acid therefore wet aged product may have a slightly sour taste or odour when compared to the Pseudomonas that do not produce any sour flavours on dry aged meat.

Dry aged beef is considered a gastronomical treat and is commonly found in some of the finest restaurants and butcher shops. Premium dry aged beef products usually come from grain fed cattle due to the greater marbling within the meat. Extremely lean meat will spoil if aged. The flavour of dry aged beef can range from buttery to nutty and almost gamey depending on the age and storage conditions. The flavour is also dependent on other factors such as the quality of the meat cut, whether it is grass fed or grain fed, storage temperature and relative humidity during ageing. Premium products can be dry aged for up to 6 weeks provided the process meets the requirements of these guidelines. It may be difficult to maintain the wholesome of meat after 8 weeks of dry ageing.

The Processes

1. Enzymatic action

Endogenous proteolytic enzymes from the meat itself as well as from the specific beneficial moulds weaken the structural myofibrillar proteins in the meat. This takes 10 to 14 days and results in a more tender meat. At this stage the meat flavour can usually be described as buttery and smooth.

2. Evaporation

Loss of water from the meat by evaporation causes concentration of the remaining proteins and increases flavour intensity to a nutty almost gamey taste. Final water loss can be up to 50 per cent and depends on the relative humidity used during drying.

Control Factors

3. Temperature

A storage temperature between -0.5°C to 1°C should be used. A temperature of between 2°C to 3°C may be used when the meat is only aged for 2 to 3 weeks. Frozen or thawed meat must not be aged because the desired enzymatic action will not occur, and mould growth will not be initiated on the surface of the meat. The temperature must be recorded daily throughout the ageing process to ensure the wholesomeness of the meat is maintained in compliance with the requirements of Australian Standard for the Hygienic Production and Transportation of Meat and Meat Products for Human Consumption (AS 4696:2007).

4. Relative Humidity (RH)

Control of RH is important because it restricts growth of pathogenic bacteria by drying the meat surface resulting in the formation of a crust. This also reduces bacterial growth on the surface in preparation for growth of the desirable Thamnidium mould. A RH of between 75% to 85% is recommended and actual RH should be recorded daily for the duration of the ageing process. Lower RH may be used but tends to dry out the meat and contribute to higher trim losses in the final product. Higher RH should not be used because it will result in spoilage of the meat before ageing is complete.

5. Air Flow

To prevent spoilage, portions of meat must be adequately separated from each other to allow efficient and controlled air flow between each portion. The desirable air velocity is 0.2 to 0.5 m/s and can be controlled with a properly designed refrigeration unit and fans. The air velocity and flow should be kept uniform for the duration of the drying process and is most critical at the start of the dry ageing process.

6. Cross contamination

Dry aged meat must be segregated from all other meat products. Dry ageing must not be conducted in chillers where other fresh meat is stored. Purpose built rooms and cabinets must be used for the dry ageing of meat. Trimming and preparation of product for packaging and sale must be segregated from areas used for fresh meat. Dry aged meat products must not be displayed in retail display cabinets with other fresh meat. Designated cabinets and/or chillers must be used.

7. Antibacterial Strategies

The use of ultraviolet (UV) light for destruction of bacterial cells is well known for fresh meat. A more sophisticated approach to manage the dry ageing process is to install UV lighting entirely and leaving no other light source. Air can also be circulated through UV lit chambers however the costs may be prohibitive. The use of antibacterial rinses for the preparation of meat for dry ageing has some inherent risks and must be validated and approved.

8. Microbiological

Dry ageing involves restricting bacterial growth and encouraging the growth of beneficial mould. During the dry ageing process, mould from the Thamnidium, Penicillium, Rhizopus and Mucor genera can be found on the surface of the meat. The most desirable is the Thamnidium mould as it has been shown to releases proteases that tenderise ageing meat. Other mould species have been associated with infections in humans and production of harmful natural toxicants. They also do not provide any favourable characteristics for ageing of meat.

Wet ageing of meat describes a general storage process that occurs after a carcass is broken down or boned. The wet ageing process commences when meat is packaged and stored. If vacuum packed meat is aged, then it must be validated as being wholesome and fit for human consumption (see Shelf Life and Labelling Requirements for Meat Products PrimeSafe Technical Guideline).

The process

1. Enzymatic action
Endogenous proteolytic enzymes weaken the structural myofibrillar proteins in the meat. This takes 10 to 14 days and results in a more tender meat. Meat is aged in its own blood and serum therefore growth of Lactobacilli can result in a sour and subtle flavour compared to dry aged meat.

Control factor

2. Temperature
A storage temperature below 5°C must be used. Frozen or thawed meat must not be aged because the desired enzymatic action will not occur, and mould growth will not be initiated on the surface of the meat. The temperature must be recorded as required in the food safety program throughout the ageing process to ensure the wholesomeness of the meat is maintained in compliance with the requirements of Australian Standard for the Hygienic Production and Transportation of Meat and Meat Products for Human Consumption (AS 4696).

Product testing is required for:

• Initial approval and annual validation.
• Any change to the process.

The dry ageing of beef can be for up to eight weeks, depending on the product characteristics required. The ageing conditions will determine the shelf life of the final product. Dry aged meat products must be tested for mould to validate the procedure. Growth of Thamnidium mould can start from three weeks after commencing the ageing process. Testing involves removing a 100g portion of untrimmed aged meat that includes visible mould if it is present and sending it for testing at a NATA accredited laboratory. If testing for mould shows that the results are positive, then confirmation that the mould is Thamnidium must be conducted.

For wet aged meat products there will be no growth of mould due to the lack of oxygen in the bag therefore there is only a requirement to confirm the wholesomeness of the product.

Processed (trimmed) and packaged dry aged meat cuts generally have a shelf life of two to three days. For this reason, meat is trimmed just before sale. To confirm the wholesomeness of dry and wet aged products, the shelf life must be validated by testing for Enterobacteriaceae and E. coli. These two tests must be conducted at the end of the desired shelf life following the ageing period to validate the wholesomeness of the final product at the point of sale. The critical limits for wholesomeness for these purposes are microbiological limits of Enterobacteriaceae of 1,000cfu/g and E. coli of 10cfu/g. Five 10-gram samples must be taken for testing of both Enterobacteriaceae and E. coli. Composite testing of the samples is permitted at the laboratory.

All procedures and records must be submitted to PrimeSafe before approval of your process may be granted.

Testing flow