Why is my stock fat floppy?
March 16, 2017 2:49 PM   Subscribe

I make 50-something gallons of stock a week at the restaurant where I work. We make the stock from roasted bones; beef, chicken, veal, etc, no veg. We make the stock in either a steam kettle or a very large pot. Sometimes the fat, when cooled, creates a very solid layer on top of the stock. Sometimes it is mushy and soft like a slushy. What gives? , I still haven't figured out the variable that creates a soft or hard fat layer.

Temperature? Duration (we usually simmer for one or two days)? The bones themselves? Roasting time? Something else? This happens to all the varieties of stock, but only sometimes. Give me your food-chemistry wisdom.
posted by Grandysaur to Food & Drink (11 answers total) 3 users marked this as a favorite
Different animal fats will solidify differently. Beef fat almost always will form a thick, solid layer that will be less mushy. The rate at which you cool the stock also has an impact. The more emulsified a fat is, the more likely you are to get that mushy layer on top. If a stock is cooled sufficiently quickly, complete separation of the fat may not occur, and you're more likely to get that mushy texture. Also important is how much skimming is done to the stock, if the stock is stirred after it is strained, and how far the stock has reduced. As a cook, unless you're using the exact same amounts of every ingredient, and cooking for the exact same period of time for every stock, you're bound to get these variances as even ambient temperature can make a difference.
posted by carmel at 3:00 PM on March 16, 2017 [4 favorites]

Even the area of the animal can make a difference, the legs and feet of animals tend to be cold, the fat from these areas can be much more liquid (i.e. neatsfoot oil comes from the feet/lower legs of cows and remains liquid)
posted by 445supermag at 3:15 PM on March 16, 2017 [5 favorites]

Response by poster: Just to clarify, all of the stocks are cooled the same way -- in buckets in the walk-in, which is usually the same(ish) temperature.
posted by Grandysaur at 3:22 PM on March 16, 2017

The thick layer of gelatinous fat is good thing. You're pulling collagen out of the "jointy" bones and basically making gelatin. It'll melt when reheated and provide the rich texture you want.

More gelatinous fat: more neck bones, more feet bones, less water, a softer boil.

Less gelatinous fat: more of the middle of bones/bigger bones, more water, a rolling boil.
posted by flibbertigibbet at 3:23 PM on March 16, 2017 [4 favorites]

To second one aspect of what carmel says (although I agree with all of it) I definitely find that faster cooling produces a slushier fat layer. If fat is only solidifying​ once it reaches the cooling surface, then it will tend more towards forming a solid layer, as it only hardens in the presence of other fats. If you're following best practice and cooling the whole pan quickly, fat is more likely to solidify while it's rising, and bring some stock up with it to the surface, trapping it there.
posted by howfar at 3:24 PM on March 16, 2017 [2 favorites]

Oh, and you can always buy gelatin sheets or packets and add one in if you feel you're producing a 'softer' broth despite your best efforts. Serious Eats says 1 packet softened in 1/4 cup water.
posted by flibbertigibbet at 3:25 PM on March 16, 2017

"Gelatinous fat" is an oxymoron. Gelatin is a protein, jelly in stock is a gel of that protein in water. Fats are, um, fat. You can have a totally fat-free stock that sets into strong jelly.

Whether fat is hard at refrigerator temperature is a function of the proportion of saturated fats. Scale would be lamb/mutton tallow -> beef tallow -> pork lard (or coconut oil or palm oil) -> poultry fat. As other people noted, freezing speed has a bearing on whether you've got a truly 100% fat layer there, and some stock mixed in will make it a bit grainy and hence less solid. But if pure fat, mutton fat is going to be hard compared to chicken fat.
posted by i_am_joe's_spleen at 3:54 PM on March 16, 2017 [13 favorites]

Collagen. And collagen is not fat. More collagen in the bones that's extracted, the more solid the gelatin that forms when the liquid is cooled.

Fat that cools and hardens is more opaque and brittle. Pretty sure you are talking about collagen.
posted by jbenben at 5:37 PM on March 16, 2017

Best answer: I have also made a lot of stock in professional kitchens and can attest that a seemingly consistent process + set of bones can yield a fat layer with varying levels of softness. It has something to do with water content for sure, and if anyone thinks the raft of fat at the top of their refrigerated stock has no water in it, try scraping some off and heating it up in a dry pan, I'll bet you a dollar it starts to sputter.

Something must be affecting the way the fat and water are separating. I agree with those who say it's the rate of cooling, but have never done a controlled experiment. You say you always cool them the same way, but do you always cool the same quantity at once? Even cooling two buckets vs one will take more time in the same walkin, all other conditions being equal, to say nothing of how busy you are that night and how many times people are opening the door.
posted by STFUDonnie at 5:37 PM on March 16, 2017 [4 favorites]

i have noticed that i more consistently get the floppy "wetter" fat layer with poultry stocks more than pork or beef.
posted by Exceptional_Hubris at 8:38 PM on March 16, 2017 [2 favorites]

My suggestion would be that it depends on various kinds of fat derived from different species of animals and/or areas of an animal. The proportion might vary between batches.
This is about melting points and overall firmness and softness. Chicken fat stays soft, often liquid at room temperature. Lamb fat and some beef fat gets very firm. Some other beef fat gets not quite as hard, for instance anything that comes from marrow bones tends to stay soft. Pork: also soft, but with a higher melting point than chicken fat.
Duration and temperature when making the stock may factor in when it comes to extracting the fat, and hence might influence the overall balance, but I'd think that it's most of all a question of what enters the pot, in which proportions.
posted by Namlit at 4:20 AM on March 17, 2017 [2 favorites]

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