S.O.S., Bacon Fat Roux

Half bacon fat, half butter — with the one correction that nobody makes. Butter is only about 81% fat; bacon fat is about 100%. Swap them one-for-one and you haven’t made the same roux, you’ve made a fattier, looser one. So the bacon fat here is cut by about a fifth. That arithmetic is the only real physics in this whole argument, and everything else about it is taste.

Ingredients

• The roux — note the deliberate mismatch
• 5 tsp (1 Tbsp + 2 tsp) butter
• 4 tsp bacon fat — this is 4 tsp standing in for 5 tsp of butter. That’s the ~20% correction.

¼ cup (4 Tbsp) all-purpose flour

• The rest
• 2 cups whole milk
• 8 oz chipped or dried beef

¼ tsp black pepper

• Salt — only at the end, and only if it needs it. Read the notes first.
• 4 slices toast

Directions

Key ingredients

Bacon Grease · Black Pepper · Chipped (Dried) Beef

1. Separate the beef into small pieces. Taste a piece. How salty it is decides the rest of the recipe.
2. Melt the butter and bacon fat together in the pan. The butter will foam — that’s its water boiling off, and it’s the reason the two fats aren’t interchangeable.
3. Add the flour and cook it, stirring, until it’s smooth and just barely blond. Keep it pale. The roux’s colour drives thickening about four times harder than the fat choice does — take it dark and you’ll lose the body you came for. If you want the browned-roux version, that’s the 1910 dish: S.O.S., Army 1910 (Brown Gravy).
4. Add the milk gradually, stirring constantly, until smooth.
5. Add the beef and the pepper. Bring to the boil, drop the heat, and simmer about 10 minutes.
6. Now taste. Then decide about salt. Not before. See the notes — this is the actual hazard of this recipe and it isn’t chemistry, it’s seasoning.
7. Serve on toast.

Notes

⚠ NOBODY HAS TESTED THIS. Start there.

I want to be straight with you before I say anything else: there is no controlled test of a bacon-fat roux versus a butter roux anywhere I could find. Not Kenji, not Cook’s Illustrated, not McGee. Every confident claim you’ve read about this is folklore. Mine included, except for the arithmetic below.

(Serious Eats blocks automated access, so “not found” there means not found, not “does not exist.” Flagging that rather than papering over it.)

⚠ SALT IS THE REAL HAZARD

This is the part that will actually ruin your breakfast. Bacon fat is already salty. Chipped beef is very salty — salt isn’t seasoning in a cured product, it’s the preservation method, it’s structural. Stack the two and season out of habit and you’ve made something inedible.

Season at the very end. Taste before you add any salt at all. The 1910 manual acknowledged the same problem in its own way (“if the beef is very salty, it should be scalded”) — though don’t blindly scald the modern jarred product, which is much milder than the historic article.

The one real effect, and it’s the only number here

Butter is 80–82% fat, 16–17.5% water, ~1% milk solids. Bacon fat is essentially pure fat — rendering is the process of driving the water off.

So 1 oz of butter delivers ~0.81 oz of actual fat; 1 oz of bacon fat delivers ~1.0 oz. About 20–23% more fat for the same measured spoonful.

The fix: use ~20% less bacon fat than the butter called for — roughly 4 tsp bacon fat per 5 tsp butter. (For the 1910 recipe’s 1 lb of butter: about 13 oz of bacon fat.) That’s what the ingredient list above is doing.

Secondary, and small: you also lose butter’s water, which flashes off during the foaming and never reaches the sauce. Bacon fat has none, so the gravy runs very slightly looser. Swamped by the ratio point.

Two popular claims that are just wrong

• “Bacon fat has a lower (or higher) smoke point, so it’s better/worse for a roux.” The sources put butter at ~350°F and bacon fat at 325–375°F — within about 25°F of each other, and neither fat’s triglycerides are the limiting factor at roux temperatures. What fails is the solids: butter’s milk solids brown then burn; bacon fat’s residual meat solids do the same thing.
• “It thickens differently.” No. The flour thickens; the fat disperses — it coats the flour particles and stops lumping. And the variable that genuinely matters is colour: a chocolate roux has about ¼ the thickening power by weight of a white roux. That’s roughly a 4× effect, which is larger than anything the fat choice could do.

So why do it at all?

Flavour, and flavour is a preference, not a fact. Bacon fat brings smoke phenols and pork aroma; butter brings dairy lactones and, if you brown the solids, a nutty backbone. Half and half is what I’d cook: enough bacon fat to carry smoke into a gravy that is pale and salty and needs the help, enough butter that the milk solids can still do their job.

And the joke at the end of it — the 1910 manual says “1 pound fat, butter preferred.” Fat was the default; butter was the upgrade. This isn’t a modern hack.

Serve it on

Grit Cakes, Fried Cheese, or run the fourth arm: Polenta for S.O.S.