Sous-vide tough cuts
Meat can be thought of as muscle fibres made up of protein strands bundled together and encased in collagen sheaths for support. In land-dwelling animals, the collagen sheaths extend beyond the muscle fibres and intertwine to form the tendon that attaches to bone and gives muscle its leverage. Meat contains enzymes that are important for tenderizing, water (~70%), water-soluble flavour compounds and fats.
Tenderising tough cuts means breaking down the muscle proteins and the collagen (which is also a protein). There are 3 considerations.
The first stage occurs at and after slaughter. The cook does not have control over this, nor is this information usually available. Consumer pressure advised.
The second stage occurs with ageing. Enzymes are freed from their control mechanism and start to indiscriminately break down proteins into pieces. This not only tenderizes, but adds flavour, as the pieces are amino acids that we can taste. To some extent enzymes may also break down collagen, although this is less accepted.
Beef (in particular) is aged to allow time for this process to occur. It is a slow process under refrigeration.
There are many meat enzymes, but two are most relevant for tenderizing — calpains and cathepsins. Enzyme activity increases with temperature up to the denaturation point of the enzyme. This is 40C for calpains and 50C for cathepsins. Holding meat just under these temperatures will result in greatest enzyme activity and therefore tenderness. Taking it too far results in mushiness.
Unfortunately, these are not food safe temperatures to hold for any length of time. Even if meat surfaces have been rendered safe by heat (searing, torching, blanching), the meat has only been pasteurized, not sterilized. There is potential for a relatively few remaining bacteria to multiply and become problematic if temperatures ~40C are held for extended periods of time. Four hours would be the limit. A brief wet-age can be done in a home fridge.
The third process is cooking. Above ~60C, collagen begins to transform into gelatin. It is the same molecule, it just takes on a different shape. With tough cuts, it is usually the collagen that limits tenderness and that needs to be gelatinized (a better term is hydrolyzed).
Unfortunately, as collagen is heated it shrinks as well as gelatinizes, wringing out juices and drying the meat. Collagen has a helical structure that twists as it shrinks. It unravels as it gelatinizes.
So the aim is a temperature just above the point where gelatinization starts, but low enough to minimize shrinkage. This is where sous-vide comes in.
The gelatinization process will be slow at these temperatures. Therefore sous vide tough cuts are generally cooked for 24–48 hours, or longer! Luckily, sous vide is unattended cooking.
Tough cuts can also be pressure-cooked and will be fall-apart tender because virtually all the collagen will be gelatinized. However, the meat will also dry out because of the high temperature (even if it is cooked in liquid — in fact, more so if it is, but that’s by another mechanism). If the cut contains sufficient collagen it can withstand this treatment because the gelatinization will mask the absence of juices and the meat will still taste succulent.
A note on terms: juiciness refers to the initial burst of juice in the mouth; succulence refers to the continued sensation of juiciness. Thus, oranges are juicy but not succulent.
Finally, I’ve got around to the point of this post — simplified sous-vide suggestions for tough cuts:
Beef, lamb and pork ~60C for 24–48 hours. Seafood (squid, cuttlefish) ~ 65C for 5h.
Exceptions or alternatives:
Octopus (85C, 4h). Pork belly (84C, 4–8h). Modernist Cuisine suggest oxtail at 60C for 100h! 65C for about half that time might be more practical.
A downside for sous-vide tough cuts is that the water bath is tied up for days. If the bath is needed for another cook, just remove the meat, adjust temperature and cook whatever is needed at the time, then readjust temperature and continue with the slow cook.