Vol. XVIII · Meat and Poultry Plate 5 of 11marinade, marinating, acid, vinegar, citrus, yoghurt marinade, enzymes, papain, bromelain, pineapple, kiwi, soy sauce, penetration, flavourMF

Marinades.

An overnight marinade does not soak through a chicken breast. Cut one open: the flavour is in the outer few millimetres, and the rest is plain chicken.

A marinade is a flavoured liquid: usually something salty (salt, soy sauce, fish sauce), something acid or enzymatic (vinegar, citrus, wine, yoghurt, pineapple, kiwi, papaya), aromatics (garlic, ginger, herbs, spices) and often oil. Each part moves into the meat at its own pace. Salt, a small ion, diffuses fastest — a few millimetres in hours (XVIII.4). Acids get in more slowly because the meat's proteins buffer them as they go. Larger aroma molecules crawl, and the many that dissolve in oil but not water hardly enter at all.

So marinades work at the surface — which is where most of the taste is, especially once it browns. Their tenderising claims are mostly false: acids and enzymes act on the outside first, and given time they turn the surface mealy or mushy (pineapple's bromelain and papaya's papain can liquefy it in hours) while the inside is untouched. Yoghurt and buttermilk are gentle: mildly acid, and good at carrying spices and browning, as in tandoori chicken. The workshop compares depths.

Below: how deep salt, acid and a typical aroma molecule have reached in a 25 mm piece after the hours you choose in the fridge (diffusion with teaching diffusivities for each, to where the concentration reaches a tenth of the marinade's).

What you will learn

Explain what a marinade does and does not do.
Compare penetration of salt, acid and aroma.
Avoid over-marinating with acid or enzymes.
Design a marinade that works.

Workshop

Fick's law in a 25 mm slab at 4 °C. Teaching diffusivities: salt 4 × 10⁻¹⁰ m²/s; acid 1.5 × 10⁻¹⁰ (slowed by the meat's buffering); a medium aroma molecule 5 × 10⁻¹¹. Depth is where the concentration reaches a tenth of the marinade's. Oil-soluble flavours are not modelled: they largely stay in the oil.

Flavour the surface, then brown it

After eight hours, salt has reached about 5.6 mm, acid about 3.5 mm and a typical aroma molecule about 1.9 mm; even after two days the aroma is only 4.8 mm in. A marinade is a surface treatment. That suggests what works: salt (or soy sauce) in it, so it seasons and brines; thin cuts, skewers or scored surfaces, which give it more surface; enough time for salt (an hour to overnight) but not so much acid that the surface turns mealy; and flavour that will be on the surface, where the browning happens. Much of the marinade's flavour is best added again as a glaze or sauce.

Specific limits: citrus or vinegar marinades for fish an hour at most (it starts to "cook", as in ceviche, XIX.6); for chicken a few hours. Pineapple, kiwi, papaya, fig or ginger with active enzymes: under an hour, or the surface turns to paste. Yoghurt: overnight is fine. Oil carries fat-soluble aromas (garlic, chilli, herbs) to the surface and helps heat transfer, but those aromas stay outside. Discard used marinade from raw meat, or boil it before using it as a sauce (XII.8).

At the stove

Marinate two chicken breasts overnight in a soy, garlic and ginger marinade; cook one whole and cut the other into strips before marinating. Taste the centre of the whole one against a strip.

In the 1950s, papain from papaya was sold as "meat tenderiser" powder; a test by food scientists found that it mostly turned the surface to mush, much as fresh pineapple does to a gelatin dessert by digesting its proteins.

Terms

Marinade: A flavoured liquid that meat soaks in before cooking.
Penetration: How far a substance has moved into the meat.
Proteolytic enzyme: An enzyme that breaks down protein: papain, bromelain, actinidin.
Mealy: A soft, grainy surface from too much acid or enzyme.

Marinades flavour the surface: salt goes a few millimetres, acid less, aroma barely. Acids and fruit enzymes mush the outside rather than tenderise the inside. Put salt in it and don't over-acidify.

Sources

A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.