Ageing Beef More (or Less) Gracefully

While consumers may value a wide range of attributes when deciding what type of beef to buy, they are united in what the most important quality is when they eat it - tenderness! My Grandfather, who was a butcher, passed down this quote to my Dad: "a tough steak is dear at any price." My Dad added his own nugget of wisdom regarding beef quality: "if I need a steak knife to saw through the meat, I don't want that steak."

Retailers deal with the sharp end of the beef supply chain, and they know that tough beef hurts sales and long term customer relationships. One of the main methods of improving beef tenderness after slaughter is ageing - a time period when the carcass or sections of it are refrigerated to allow natural enzymatic breakdown of tough fibres within the muscle tissue.

The effect of the length of the ageing period has been extensively investigated, but most research has focused on the loin and rib-eye muscles. It had been assumed that all muscle cuts responded similarly to extended ageing, but some early research had shown that this is not necessarily true.

An experiment at the Agriculture and Agri-food Canada Lacombe Research Centre, reported by Juarez et al, investigated the effect of extended ageing on 6 different sub-primal cutsi. The meat was from a commercial abattoir and was shipped directly to the research station. Research staff sliced 1 inch thick steak retail cuts from the wholesale cuts which represented the various parts of the carcass (Table 1 and Fig.1). Samples were stored at either 1* or 5*C to evaluate the effect of cooler temperature on tenderness and flavour. Samples were cooked and evaluated weekly, starting on arrival (0 days of ageing), and up to 56 days of ageing.

Table 1. Meat cuts evaluated

Retail Cut
Wholesale Cut
Striploin
Loin
Blade-eye
Chuck
Outside round
Outside round
Inside round
Inside round
Eye of round
Outside round
Chuck tender
Chuck

Image of different cuts of beef
Figure 1. Sub-primal cuts of beef

After cooking, the samples were cooled and placed in a cooler at 1*C for 24 hrs, after which cores were taken and measured for the force required for a blade to shear across the meat fibres (Warner-Bratzler shear force). A higher shear force means that the meat would be tougher to chew.

Tenderness

Storage temperature did not affect shear force for any cut. However, ageing significantly reduced shear force for the striploin, blade-eye, eye of round and chuck tender(see Fig. 2).Surprisingly, the outside round showed a significant increase in shear force over time, up to day 21, then trended downwards until day 49, when it was similar to day 0.In contrast to this, the shear force for the inside round did not change with ageing time. The reductions in shear force for the eye of round and chuck tender were not great, and did not reach values significantly lower than day 0 until day 35. Shear force decreasedover time in a linear manner for striploin, blade-eye and eye or round up to day 35, after which values tended to stabilize. The chuck tender experienced a decline in shear force until day 35, with subsequent measures showing up and down trends.

Graph showing the effects of ageing on tenderness

Why didn't all of the cuts show increased tenderness over the ageing period? The authors propose that for muscles which initially showed increased tenderness with ageing, followed by a period of increased toughening, loss of moisture within the tissue could be one cause of the increase in toughness. Decreased moisture loss leads to increased cooking times, since heat transfer rate is reduced as water content decreases. Increased cooking time would lead to even more moisture loss and subsequent toughening of the meat. Another factor may be related to the collagen connective tissue in the meat. The presence of moisture helps to soften the connective tissue during cooking, so low levels would inhibit this softening effect. For cuts which undergo initial toughening, followed by increased tenderness, enzymes which become active only late in the ageing process may be the cause.

Sensory Evaluation

A trained sensory panel evaluated cooked steaks from each of the cuts at each of the ageing times. The panellists gave scores for initial tenderness (first bite), overall tenderness (after 25 chews) and for intensity of beef flavour and off flavour (10 -20 chews). Ageing increased initial tenderness scores for striploin and blade-eye, and overall tenderness scores for striploin, blade-eye and eye of round. Ageing decreased tenderness scores for outside round and inside round. No ageing effect was found for initial tenderness scores for outside round, inside round, eye of round and chuck tenders, and overall tenderness scores for chuck tender. In general, flavour intensity scores decreased as ageing time increased, while off flavour scores increased with ageing.

Discussion

These results show that the process of ageing is not uniform with increased time, and different sub-primal cuts showed dramatic differences in response to ageing. For example, ageing decreased the force needed to shear cores from striploins up to 35 days, after which additional ageing had no effect, while the outside round needed considerably more shear force with ageing up to 35 days, after which shear forcedecreased, becoming equivalent to the initial value by day 49. In contrast, ageing did not affect the shear force for the inside round. Increased ageing resulted in an overall negative effect on the flavour of the meat.

While these finding are important for all players in the beef processing and retailing sectors, it is particularly relevant to branded beef value chains that have the ability to prescribe specific ageing and marketing strategies for different sub-primals. In concert with this, it is important to realize that increased ageing of some cuts is actually detrimental to quality, while for others increased ageing incurs storage costs without producing benefits.

i Juarez, M., Larsen I.L., Gibson,L.L., Robertson, W.M., Dugan, M.E.R., Aldai, N. and Aalhus, J. 2010.Extended ageing time and temperature effects on quality of sub-primal cuts of boxed beef. Can. J. Anim. Sci. 90: 361-370.

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