Letting food cool down

Hi! My name is Yen and I'm from Kuala Lumpur, Malaysia. I've been glancing through the forums and didn't seem to find anything in relation to a difference between "cooling down" (or resting for meats) or shock cooling of food to preserve moisture ,vegs, creme brulees, or particular gelatinous cuts like oxtails etc. This query is coming off the back of one of blumenthal's episodes on beef, where he puts a statement on allowing oxtail to completely cool to retain moisture before utilising it

Would that theory hold true for other types of food? of course given the difference in molecular structure I wouldn't expect vegs to behave the same as proteins but would it improve, lets say, the creaminess of a creme brulee on a slower temp cooling method (leaving it in the pot to cool down from 80'C vs of a shock freeze,(chucking it into a freezer) or would it completely mitigated by sous vide?

Find more posts tagged with

Hi! My name is ________!

Comments

Martin_411586

My guess it's about the gelatin (proteins) which gels when it cools down. The gelling traps moisture and melts again when reheated.

This gelatin comes from connective tissue that breaks down under heat (and time), which is quite abundant in cuts like ox tail.

tshewman

For proteins, as they heat ad molecules move faster, sarcomeres (muscle fibers) shorten and moisture is excreted. By allowing the meat to rest, they are allowed to relax (assuming room temp is cooler than cooking temp) and sarcomeres lengthen and moisture is retained. With veg, the cell walls are broken down and thus they can't reform into whole units once again so the moisture that is lost is not reabsorbed (but external moisture can be absorbed). using SV however, this allows us to trap the moisture of he plant/veg and use it if desired (e.g. use it in a puree of the same veg). Egg proteins denature and are not thermo-reversible. In other words, once they become unraveled they stay that way and do not relax and "reset" to close to original shapes (microscopically).

Martin_411586

We normally talk about water-soluble proteins in these cases. As heat increases, the speed at which the particles move increases, causing instability to the tertiary structure of the protein (it's folding), causing it to denature (unfold). Water is usually the main force keeping a protein folded and the bonds aren very strong (except for the disulfide bridges). Some water is lost, but a lot of water normally remains in the network that is formed by the denatured proteins. The egg white in a fried egg is a good example of retaining water in a gel of denatured protein.

These fibres don't really shorten, they unfold to lose structure (tertiary protein structure) and gain another: a random network of proteins that tend to aggregate / bind on their water-insoluble domains (hydrophobic).

Sorry to get technical, but it's interesting matter

Yen_342891

I appreciate the technicality, after all, that's why i posted the query in the first place. I'm now curious whether this theory holds true with freezing food (water leeching out of frozen protein) and speeding up of defrosting methods (hot water) vs gradual increase in tempreature differential between frozen food and liquid surrounding the frozen food.

tshewman

Thanks Martin, agreed! The water soluble distinction is important and helps understanding how different products with proteins react to heat. From a cook's perspective, this makes things more predictable to deal with.

tshewman

water will remain inside and outside the product and may crystalize over time (so it depends on how long it's frozen, access to oxygen etc etc). Because muscle tissue has allot of water, there will be some structural change if frozen for long periods. So you will get denaturation and aggregation. What Martiz suggests is also important as with more gelatin, more water, diff ratios across diff cuts.

Martin_411586

The ability of water to form hydrogen bonds with proteins changes when you freeze the water, I suppose. I'm note sure that's the main culprit here though, that might be sublimation (freezer burn). Besides temperature, the other drivers of this irreversible denaturation of proteins are pH (think: raw fish and lime juice) and salts. So beside drawing moisture from the cells through osmosis, salts/sugars and other dissolved stuff also denature proteins (from a certain concentration and up).

Martin_411586

Cooling of starches (brulee with corn starch, cooling of potato chips between cooking phases like Heston does and the same for mash) and fats re-crystallises them. The speed at which the food cools influences the structure that is formed in some cases, pretty much the same as with hardening steel through heating/rapid cooling. If you were to cool it slowly, you would end up with another crystalline structure.

One of the best examples is the fat in chocolate: it can crystallise in six different shapes. Same fat, different structure with different properties.

One of them is the one we all like, another one is what we call chocolate bloom, etc. The process that yields the structure we like is called tempering.