Hey {{first_name|there}},
Welcome to number two of open kitchen. Last week I said fat and heat get all the attention while salt and acid do the real work. So obviously this week is about fat hahah. Because almost everyone cooks with oil and butter every day, and almost nobody knows why they grab one over the other.
So this one is about the three fats you already have at home: neutral oil, olive oil and butter. When to use which, and when to keep your hands off the good bottle.
Why it matters
Fat does three jobs in cooking: it moves the heat from your pan into the food, it carries flavour, and it gives texture, like crispy skin or a glossy sauce. Every fat is good at different jobs.
In every restaurant kitchen you'll find the same three things next to the stove: a squeeze bottle of neutral oil, a block of butter and a bottle of olive oil. All of them get used, often in the same dish, never for the same reason.
The simplest way to think about it: neutral oil is for heat, butter is for flavour, and good olive oil is for the finish.
Which fat, when
Neutral oil
Use it for real heat. Searing meat, crisping fish skin, stir-frying, deep frying.
"Neutral" just means it tastes of almost nothing. Sunflower, corn, grapeseed, peanut and regular rapeseed oil. Most of them can take a lot of heat, but not all the same, so check the chart below.
Use it when the ingredient should be the star, like in herb oils, chili oil or the base of a mayo.
Sidenote, my personal favourite: cold pressed rapeseed oil. Not neutral at all hahah. It's more expensive, but it tastes almost like butter in oil form. Perfect for gently frying stuff where you want that flavour to go in, like eggplant. Keep the heat low though.
The chart below shows rough smoke points: the temperature where a fat starts to break down. Go past it and the oil smokes, tastes bitter and burnt, and forms compounds you don't want to eat or breathe in. Think of it as each fat's speed limit.
Olive oil
Think of it as two bottles: extra virgin for flavour, and olive oil 0.4 for cooking.
Extra virgin goes on at the end. Soup, burrata, grilled fish, ripe tomatoes, dressings. Heat kills that fresh, peppery taste you paid for, so frying with it is basically burning money.
Olive oil 0.4 is your frying olive oil. It's refined olive oil with a bit of virgin oil blended back in. The 0.4 is its acidity, and lower acidity means it can take more heat before it smokes. Best of both worlds: you can fry with it and it still tastes like olive oil, just milder. You'll see it everywhere in Italian kitchens.
Butter
Butter is where the flavour comes from. Nothing else tastes as rich and round.
Baste at the end of a sear. Sear in neutral oil, and when it's almost done, turn the heat down, add a knob of butter, garlic and thyme, tilt the pan and keep spooning that foaming butter over. That's the restaurant steak.
Whisk cold butter into a sauce right before serving (the French call it monter au beurre) for body and shine. That's an emulsion, more on those in the recipe.
Brown it until the bits at the bottom turn golden and it smells like hazelnuts. Amazing on fish, veg, pasta and basically every dessert.
Baking has its own rules, so that's getting its own issue soon.
What to look out for
Butter burns fast on its own. The milk solids burn way before the fat does. Start with oil and add the butter once the heat comes down, or use clarified butter or ghee if you want butter flavour at high heat.
Get it hot, but not smoking. Your oil is ready when it shimmers and moves around the pan almost like water. Smoking hard means burning, and that taste goes straight into your food.
Ever noticed olive oil comes in dark bottles or tins? Light and heat make it go stale and flat. Restaurants keep it in clear squeeze bottles next to the stove, but they empty three of those a day, and the big stock sits in a cool, dark storage room. Not finishing your good bottle this week? Dark cupboard, away from the stove.
Don't blend extra virgin olive oil. It's full of polyphenols, healthy antioxidants that taste bitter on their own. The fat normally keeps that in check, but a blender smashes the oil into tiny droplets and sets the bitterness free. Whisk it in by hand instead.
Salted butter is seasoning. Same as last week: count it before you reach for the salt.
That polyphenol bit was a little nerdy. Too much, or more of that? Tap one below, it takes two seconds.
How deep do you want me to go?
Try it this week
Fry three eggs on medium heat: one in neutral oil, one in olive oil and one in butter. Eat them side by side. It's the same egg, but you'll get three completely different breakfasts. That's this whole issue on one plate.
Recipe of the week: brown butter mayo
Mayo is just egg yolk and fat, so you can swap the oil for any fat you like, and brown butter is the best swap there is. Fair warning: don't make too much, this stuff is addictive as hell.
200 g butter (gives you about 160 g of brown butter)
1 egg yolk, at room temperature
1 tsp Dijon mustard
1 tbsp lemon juice
1/2 tbsp sushi vinegar
a good pinch of fine salt
freshly cracked black pepper
a good pinch of piment d’espelette (or cayenne pepper)
optional: a splash of white wine vinegar
Brown the butter until the bits at the bottom turn golden and it smells like hazelnuts. Pour it into a jug, brown bits included, and let it cool until it's just warm (too hot and it cooks the yolk). Whisk the yolk, mustard, lemon, sushi vinegar and salt in a bowl, with a damp towel underneath so it doesn't spin. Add the butter drop by drop while you keep whisking, and once it thickens, switch to a thin stream. Finish with pepper and espelette, then taste and adjust with salt, lemon or a splash of white wine vinegar.
One thing to know: butter goes hard in the fridge, so this mayo does too. Take it out 20 minutes before and give it a stir. It keeps 3 to 4 days, if it lasts that long.
Why it works
Oil and water don't want to mix. An emulsion is you making them do it anyway: you break the fat into millions of tiny droplets and hang them in the little bit of water from the yolk and the lemon. The yolk holds it together because it contains lecithin, which grabs onto fat with one side and water with the other (the mustard helps too). That's why you go slow at the start: the yolk can only wrap so many droplets at once, and if you pour too fast the whole thing splits.
Split it anyway? Don't throw it out. Whisk it drop by drop into a fresh yolk and it comes back every time. And that cold butter you whisk into a sauce? Same idea.
Until next Wednesday
That's it for number two. If you make the brown butter mayo, hit reply and send me a picture, I genuinely wanna see it. Questions about fat or anything else? Just reply too. I read everything myself.
See you next Wednesday ;)
Guillaume
open kitchen. - by table.35
P.S. Know someone who cooks everything in their most expensive olive oil? Forward them this one before they burn another bottle. They can subscribe here so the next one lands in their inbox too.