# Is Prolonged Ageing a Necessity for Improving the Quality of Sous-Vide Cooked Beef?
## 1 Introduction  
Globally, beef ranks among the three most popular meat types, following pork and poultry [1]. However, compared to poultry and pork, beef prices are higher, and the preparation of high-quality dishes from beef necessitates proficiency and culinary expertise from consumers [2]. As a result, a noteworthy proportion of consumers prefer to consume beef at restaurants or opt to purchase ready-to-eat beef products [3]. Therefore, it is reasonable to search for the most appropriate and economical methods for the preparation of beef for consumption to thereby deliver products that align with consumer preferences. It is well documented that the tenderness of beef increases during post-mortem ageing [4; 5; 6; 7]. Various beef ageing methods exist, including dry ageing, wet ageing and ageing in semi-permeable bags, with wet ageing being the most frequently employed technique [7; 8]. Wet ageing mainly consists of vacuum packaging the entire muscle or its cuts and subsequently storing it under controlled refrigerated conditions [9]. The time of wet ageing might differ depending on factors such as muscle type, the hygienic conditions of the meat and the expected outcome. An inadequate ageing time might result in undesired tenderness whilst prolonged ageing could lead to losses in lipid oxidative stability, colour and palatability of meat [7; 10], as well as increased microbial populations [11]. Therefore, it is reasonable to adjust the ageing time for a particular beef product to optimise its quality and production cost. Sous-vide cooking is a modern culinary technique that has become increasingly prevalent for the heat treatment of meat and meat products in catering services and food processing [12]. The principle of sous-vide cooking is to vacuum pack the meat and heat it in a moist environment (water bath or steam) under controlled temperature and time [13]. This technique is specifically recommended for tougher meat categories such as beef, lamb, white-striping chicken breast and spent duck meat since it enhances meat quality in terms of organoleptic characteristics and safety [14; 15]. The most frequently recommended combinations of temperature and time by chefs for beef are around 58-63 \({}^{\circ}\)C for up to 48 h. Using such low heat treatment temperatures prevents excessive changes in meat proteins and produces tender and juicy meat products [16]. Generally, meat heating causes the denaturation of myofibrillar proteins and initial denaturation, and then the solubilisation of connective tissue [17]. Since the extent of those changes is temperature and time dependent, the meat texture changes during heating. At the initial phase of heating, meat changes from tender (typical for uncooked meat) to tougher, whereas further heating to temperatures from 55 to 60 \({}^{\circ}\)C reduces this initial toughness [18]. The myofibrillar and connective tissue proteins denature at different rates, which affects the texture of the different meat cuts as well as changes related to cooking temperature. In the range from 40 to 65 \({}^{\circ}\)C, increasing aggregation of the denatured myofibrillar proteins is noted, which is accompanied by a loss of meat juice and shrinkage of the muscle fibres. At approximately 65-67 \({}^{\circ}\)C, intramuscular connective tissue fibres shrink, which increases meat toughness because of the denaturation of collagen in the endomyosin and perimysium. It also results in squeezing out the water from meat [18]. Up to 80 \({}^{\circ}\)C, the increase in meat toughness occurs, however with further increases in temperature above 80 \({}^{\circ}\)C, and prolonged heating (as in stewing or casseroling), a tenderisation is noted caused by collagen solubilisation. Collagen can be solubilised also at lower temperatures (such as used in sous-vide cooking), but this requires considerably longer cooking times than used in stewing or casseroling [18].