Kiwi, pineapple, and figs contain protein-breaking enzymes that can break down meat fibers when spread on meat, which is why they are used to tenderize tougher cuts. Their effects are very fast, however, and if the marinating time is exceeded, the meat does not just become tender—it falls apart: the surface turns powdery, the texture becomes paste-like, and this cannot be reversed. For that reason, both the amount and the time should be kept limited. The method is powerful but unforgiving.
Each of the three fruits has its own enzyme, and all of them work by cutting proteins. The enzymes act on the meat’s surface first and move inward very slowly, so the meat tenderizes from the outside in, not from the inside. If left too long, a typical problem results: the outside turns mushy while the inside is still tough. Heat deactivates the enzymes, so the process stops as soon as cooking begins. This makes them a tool that requires careful timing but can be controlled.
The amount should be modest, not generous. For 1 kilogram of meat, the grated flesh of half a kiwi or 1 slice of pineapple is more than enough. The time should be no longer than 30 minutes; it can be extended to 1 hour for thick cuts, but 2 hours will ruin the meat’s texture in almost every case. When the time is up, rinse the meat and remove all fruit residue from the surface. Leaving it overnight is not appropriate with any of these three fruits, and there is no way to rescue the meat afterward. Grate the fruit and apply it directly; squeezing out the juice does not reduce the effect, but makes it less evenly distributed.
This method is not useful for every cut. Tender cuts such as tenderloin and chicken breast do not need it and can easily be over-tenderized. It is most useful for tough cuts diced for short cooking or for meat intended for kebabs. It is also unnecessary for dishes that will cook slowly with moisture, since cooking already breaks down connective tissue and the enzyme adds nothing. With poultry, the effect is even faster, so the time is cut in half.
A few side effects should be kept in mind. The natural sugars in pineapple and kiwi can leave a slightly sweet taste on the meat and change the balance of the dish; if that is not wanted, rinse the fruit off thoroughly. The same sugar burns quickly on a grill or in a pan, so lower the heat slightly. These fruits also act on proteins in yogurt and milk when used with dairy, making the mixture watery; if kiwi has been added to a yogurt marinade, use the mixture soon.
There are slower, more forgiving methods too. Yogurt, milk, and brine tenderize meat without enzymes and can be left on for hours, with a much wider margin for error. Cutting across the grain and pounding the meat produce a similar result mechanically. If using fruit, it must be fresh: the enzyme in canned pineapple has already been deactivated by heat and will not tenderize meat. The cooking temperature does not change: bring whole cuts of red meat to 63°C / 145°F and let them rest for at least 3 minutes, and cook chicken and other poultry to 74°C / 165°F. Meat that has been over-tenderized cannot be rescued; it can only be used as ground meat or in a meatball mixture.