Eggs: gentle heat and the first emulsion

Crack an egg into a hot pan and watch it. The clear white turns opaque from the bottom up, starting where it touches the metal. If the pan is very hot, the edge bubbles, browns and goes stiff while the yolk still sits raw and cold on top. If the pan is gentle, the white sets tender and the yolk warms through slowly, and you choose the moment to stop.

That difference is most of what there is to cooking an egg, and it rests on one fact: an egg is several proteins that set at different temperatures. Learn where those temperatures are and you can boil, fry, poach and scramble to the doneness you want, instead of by a recipe's minutes. The yolk also does a second job, which is to hold oil in tiny droplets inside a little water, and that is how mayonnaise is made. This lesson covers both, and it's where lesson 4's two countries first give you different answers about what to put on a plate.

What heat does to an egg

A protein, as the American Egg Board describes it, is a long molecule folded and coiled up on itself, held in shape by "loose bonds across the folds and coils". Heat breaks those bonds and the protein unfolds. Unfolded proteins meet and join, and "millions of protein molecules join in a three-dimensional network". That is what setting is: a liquid becoming a gel or a solid.¹ It doesn't reverse. The UK's Institute of Food Science and Technology (IFST) puts it plainly: "Coagulation is irreversible, the proteins cannot be turned back into their liquid form."³ Once a white has set, cooling it won't make it runny again.

The white and the yolk are different mixtures of proteins, so they set at different temperatures. Two figures turn up in the sources read for this course:

• The American Egg Board, the US egg industry's promotion body, says "Egg white protein coagulates between 144° F and 149° F (62.2° C and 65° C); egg yolk protein coagulates between 149° F and 158° F (65° C and 70° C)".¹ The Egg Safety Center, which represents US egg producers, gives the same ranges.²
• IFST, the professional body for food scientists in the UK, gives rounder numbers: "Egg whites coagulate at 60°C, egg yolks 65°C, with full coagulation occurring at 70°C."³

They're a few degrees apart, and neither claims to be exact. The Egg Board adds that "a number of variables" change how fast eggs set.¹ What they agree on is the order: the white starts first, in the low 60s °C (the mid 140s °F), and the yolk follows by about five degrees Celsius. That gap is why you can have a set white and a runny yolk at all.

The white is two setting points, not one

There's a wrinkle that explains a lot. The white isn't one protein. A 2023 study by Jian Kuang and colleagues lists ovalbumin at about 54% of the white's protein and ovotransferrin at about 12%, with smaller shares of others.⁴ In their measurements, heated steadily in the laboratory, ovotransferrin gave way around 63°C and ovalbumin around 76°C, and they note that "many studies" of liquid egg white find two main peaks "around 65 and 80 °C".⁴ The white also gelled in two steps, at about 60°C and about 75°C.⁴

So the figure the Egg Board gives for the white, 62 to 65°C, is where the white first sets, and it is set by the smaller protein. Most of the white's protein does not let go until it is well above the temperature where the yolk sets. Putting those together, which is this course's reading of the laboratory figures rather than something either source says about a fried egg: a white held in the low 60s °C is a soft, just-set gel, and a white taken well past 75°C has its main protein set too, and is firmer. Take it far past that, as the edge of a fried egg on a smoking pan is, and you get the rubbery white everyone has eaten.

That's the whole idea of gentle heat. The temperature the egg reaches decides what you get, and the time it spends getting there decides how evenly it gets there. High heat doesn't make an egg better faster. It makes the outside overshoot while the inside catches up.

Five ways to cook an egg

Every egg method is a way of delivering heat, and each has its own way of overshooting. Lesson 2's conduction and convection are both here: conduction from the pan for frying, convection from water for boiling and poaching, and conduction from the pan with some help from trapped steam for scrambling and omelettes.

Boiled, in the shell

A boiled egg is lesson 2's thick piece in miniature. The water cannot go above 100°C (212°F) at sea level, and the heat has to be conducted in through the shell, the white and then the yolk. The white near the shell reaches its temperatures first and goes on past them. The yolk at the centre is last. So the time in the pot decides one thing: how far the heat has got into the yolk when you stop.

Two methods for a hard-cooked egg, from two US sources:

• The Egg Safety Center: put large eggs in a pan of cold water, bring it to the boil, cover, take the pan off the heat and "Let eggs sit for 12 minutes for large eggs", 9 minutes for medium and 15 for extra-large.² The water cools as it sits, so the heat is gentler at the end than at the start.
• A USDA recipe published by North Dakota State University's extension service: bring to the boil, "Reduce heat to simmer; cook for 15 minutes", then rinse under cold water straight away.⁷

Both reach a firm yolk, by different routes. Neither gives a soft-boiled time, and this course has not read a tested one, so the practice at the end has you find your own. Your time depends on your eggs' size, whether they came from the fridge, and your pot, which is exactly why it has to be yours.

Older eggs peel more easily. The US Food Safety and Inspection Service (FSIS), in its long page on eggs, explains that a new-laid white is close to neutral, "around 7.4", and becomes more alkaline as the egg ages, to "approximately 9", which loosens the white from the membrane under the shell. "For this reason, older eggs make better candidates for hard cooking."⁵

The green ring

Overcook a hard-boiled egg and a grey-green ring forms around the yolk. The University of Nebraska-Lincoln's extension service explains it: "The ring is caused by a chemical reaction involving sulfur (from the egg white) and iron (from the egg yolk), which naturally react to form ferrous sulfide at the surface of the yolk." It is "unattractive, but not harmful."⁶ FSIS says the same, adds that "a high amount of iron in the cooking water" can cause it too, and says "The green color is safe to consume."⁵

The cure is the end of the cooking, not the start. The extension page says to avoid overcooking and to cool the eggs quickly: "Run cold water over the just-cooked eggs or place them in a bowl or container of ice water until they have completely cooled."⁶ An egg taken out of hot water keeps cooking from the heat stored in it, the way lesson 7 will show a roast does, so the cold water is what actually ends the cooking.

FSIS also says hard-cooked eggs "should be refrigerated within 2 hours of cooking and used within a week."⁵

Fried

A fried egg is heated from below by conduction through the pan (lesson 2). The white touching the metal gets hot first and fastest, and the top of the white and the yolk are last. That is why a very hot pan gives you the outcome at the top of this lesson: a browned, stiff edge and a raw top.

Moderate heat fixes most of it. The other fix is to heat the top as well: put a lid on the pan for the last minute or so, which traps steam over the egg, or spoon hot fat over the top. The Egg Safety Center's guide for fried and poached eggs is to cook "until the whites are completely set, and the yolks begin to thicken but are not hard".² That is the US producers' description of safe doneness. Lesson 4's table, and the safety section below, have the rules that differ by country.

Poached

A poached egg goes straight into hot water with no shell. The Egg Safety Center gives "about 5 minutes in simmering water".² Simmering, with small bubbles, not a rolling boil.

Fresh eggs poach better, and FSIS explains why. As an egg ages, "The white would be thinner, losing some of its thickening and leavening powers. The yolk would be flatter, larger and more easily broken." FSIS's own grading advice is that its top two grades, whose whites are the firmest, "are best for frying and poaching where appearance is important."⁵ A thin white spreads through the water before it sets. A thick one stays together around the yolk.

Scrambled, and the omelette

Scrambling stirs the egg while it sets, so the network forms in pieces instead of one sheet. How hot the pan is and how much you stir change those pieces. This course hasn't read a source that tests how, so see it for yourself the next time you scramble eggs: one batch over low heat, stirred all the time, and one over higher heat, stirred now and then, and compare the curds. There's a limit on high heat you can see: FSIS says "Scrambled eggs cooked at too high a temperature or held on a steam table too long can also develop a greenish cast", the same iron and sulphur reaction as the ring.⁵

How done is done differs by country, and it's a safety rule, not a taste. FSIS says "Scrambled eggs should not be runny."⁵ The Egg Safety Center, the producers' body, is looser: its table groups scrambled eggs with fried ones, cooked until the whites are set and the yolks "begin to thicken but are not hard", and keeps its firmer wording for omelettes and frittatas, which should be "thickened with no visible liquid egg remaining."² The UK rule, below, depends on which eggs you've bought.

An omelette is the same beaten egg, set with less stirring into one soft sheet and folded. It is the method where watching someone helps most.

The same idea runs through egg dishes well beyond French and American cooking, and three are worth naming as examples of the heat, not as recipes. This course has not read a source on how any of them is made, so it describes them only as far as the mechanism goes. In a Japanese rolled omelette, thin layers of seasoned egg are set one at a time in a pan and rolled up, and a thin layer sets through before its underside overcooks. In a Spanish potato tortilla, beaten egg is set around potatoes already cooked soft in oil, over heat low enough that the middle firms before the base scorches. In shakshuka, eggs are cracked into a pan of simmering tomatoes and peppers and cooked, usually covered, until the whites set; the sauce heats the white from below and the steam under the lid does the top. In each, the cook is controlling the same thing you control in a fried egg.

Buying and keeping eggs

Before the safety rules, three habits that apply everywhere, and one test that does not mean what people think.

Don't wash them. FSIS is direct: "It's not necessary or recommended for consumers to wash eggs. This increases the risk of contamination because the wash water can be “sucked” into the egg through the pores in the shell."⁵ US eggs are washed at the plant, under controlled conditions, and FSIS's washing page adds that the washing removes the shell's natural coating, which is replaced with mineral oil.⁹ Washing again at home only adds the risk. UK eggs start from the other side: they aren't washed at all. The 2016 UK committee report described below says that washing Class A table eggs "is not permitted in the UK", so a UK egg still has its natural coating, and home washing would take it off.¹⁸

Keep them cold, in the carton, not in the door. US guidance says to keep eggs "in their original carton" in the main part of the fridge, "not in the door", which is warmer.⁸ FSIS explains why the cold matters: "A cold egg left out at room temperature can sweat, facilitating the movement of bacteria into the egg," so "Refrigerated eggs should not be left out more than 2 hours."⁵ The UK's Food Standards Agency (FSA), in its advice on eating eggs raw or lightly cooked, says to store them "in a cool dry place such as the fridge".¹²

A crack is an open door. FSIS: "Bacteria can enter eggs through cracks in the shell. Never purchase cracked eggs."⁵

The float test

Put an egg in a bowl of water, and the older it is, the more likely it is to float. The test is real, and it measures age. FSIS explains that as an egg ages, moisture and carbon dioxide leave through the pores of the shell, more air gets in, and the air cell grows, and "An egg can float in water when its air cell has enlarged sufficiently to keep it buoyant."⁵

What it doesn't measure is safety. The FSA says the float test "assesses age, not safety".¹⁰ FSIS says a floating egg is of poor quality, "but it may be perfectly safe to use. Crack the egg into a bowl and examine it for an off-odor or unusual appearance before deciding to use or discard it."⁵ That smell check is for spoilage, which you can smell. Lesson 4 showed why it cannot tell you about the germs that cause illness, and eggs are a sharp case of it, as the next section explains.

Runny eggs: the US and the UK

Here's why eggs get their own safety rules. FSIS says "Unbroken, clean, fresh shell eggs may contain Salmonella Enteritidis (SE) bacteria that can cause foodborne illness." It can be on the shell, but it can also get in "during their development inside the hen’s reproductive tract, before the shell even forms around the yolk and egg white", so, if present, it can be in the yolk or the white.⁵ A clean, cold, uncracked egg can carry it. You can't wash it off, see it or smell it. What removes it is heat, and lesson 4's principle applies: a temperature held for a time.

The two countries read that the same way and give different advice, because they're writing about different egg supplies.

The US: cook them firm, or use pasteurised eggs

The US federal message is on every carton of raw eggs not treated to destroy Salmonella: "Keep eggs refrigerated, cook eggs until yolks are firm and cook foods containing eggs thoroughly."⁵ The foodsafety.gov chart says of raw eggs: "Cook until yolk and white are firm", and egg dishes such as frittata and quiche to 160°F (71°C).⁸

FSIS spells out what that means for raw-egg dishes, and it is for everyone, not only people at higher risk: "Everyone is advised against eating raw or undercooked egg yolks and whites or products containing raw or undercooked eggs. This includes “health food” milk shakes made with raw eggs, Caesar salad, Hollandaise sauce and any other foods like homemade mayonnaise, ice cream or eggnog made from egg ingredients that are not thoroughly cooked." It adds that "Infants, young children, older adults, pregnant women and people with weakened immune systems are particularly vulnerable".⁵

The US gives two ways to make those dishes anyway:

1. Pasteurised eggs. "Use pasteurized eggs or egg products when preparing recipes that call for using eggs raw or undercooked." Pasteurised eggs in the shell "are available at some grocery stores", and "may be used safely without cooking". You cannot make them at home: "The equipment to pasteurize shell eggs isn't available for home use and it is very difficult to pasteurize shell eggs at home without cooking the egg."⁵
2. Heat the eggs in liquid first. "To make a recipe safe that specifies using raw eggs, heat the eggs separately from all other ingredients in a liquid form over low heat, stirring constantly, until the mixture reaches 160 degrees F. Then combine it with the other ingredients and complete the recipe."⁵ The mayonnaise below shows how that works in practice.

Restaurants work under a different document, the FDA Food Code, and it shows lesson 4's time-plus-temperature idea at work on an egg. A raw egg broken for immediate service must reach "63°C (145°F) or above for 15 seconds", and the Food Code's reasoning is that 15 seconds at that temperature gives a 3-log reduction of Salmonella Enteritidis in eggs, a thousandfold kill.¹³ Compare lesson 4's poultry figure, a 7-log kill, ten million to one. A restaurant can also serve raw or undercooked eggs on request, with a consumer advisory, but not to what the code calls highly susceptible populations.¹³

The US also works on the eggs before they reach you. FDA's Egg Safety Rule "requires virtually all egg producers with 3,000 or more laying hens to implement measures to prevent SE from contaminating eggs on the farm", including pest control, buying young hens "from suppliers who control for Salmonella in their flocks", refrigeration and testing.⁵ Its consumer advice still says to cook eggs firm.

The UK: Lion and Laid in Britain eggs may be runny

The UK changed its advice after a 2016 expert report. The FSA now says that young children, people who are pregnant, older people and people with an underlying health condition "can now safely eat raw or lightly cooked hen eggs" if they carry the British Lion mark or come from the Laid in Britain scheme.¹⁰ The NHS says in its pregnancy advice that such eggs "can be eaten raw, partially cooked (runny yolk), or well-cooked", and that other hen eggs "should only be eaten well-cooked".¹¹

The FSA explained its reasons when it made the change, in an announcement of 11 October 2017. An expert group set up by its Advisory Committee on the Microbiological Safety of Food (ACMSF) had reported in July 2016 that "the presence of salmonella in UK eggs has been dramatically reduced in recent years", and that the risks are very low for eggs produced under the Lion scheme's controls. The FSA listed those controls as "vaccinating hens, enhanced testing for salmonella, improved farm hygiene, effective rodent control, independent auditing and traceability, and keeping the eggs cool while transporting them from farm to shop." When the advice changed, "More than 90% of UK eggs" were produced under the scheme.¹² The committee's report put the risk from Lion eggs, "or under demonstrably-equivalent comprehensive schemes", at "VERY LOW", and from other shell eggs at "LOW". It said that such eggs "can be served raw or lightly cooked to all groups in society, including those that are more vulnerable".¹⁸ Today's FSA advice names a second scheme, Laid in Britain, beside the Lion.

Two limits come with the UK advice. It "does not apply to severely immunocompromised individuals, who require medically supervised diets prescribed by health professionals". And it is about those schemes only: "UK non-Lion eggs, non-hen eggs and eggs from outside the UK" should "always be cooked thoroughly for vulnerable groups".¹² A duck egg or an imported hen egg, in the UK, falls under the stricter rule.

Neither country is wrong

This is the first dish in the course where the two countries' rules change what you'd cook, and it's worth being exact about what the difference is. It is not a disagreement about Salmonella or about heat. It is two regulators judging two egg supplies. The UK regulator decided, on its committee's evidence, that eggs produced under particular schemes had become low enough risk to eat runny. The US agencies advise cooking every egg firm and offer pasteurised eggs for dishes that can't be cooked. The parts of the UK committee's report read here compare Lion eggs with other eggs, not with American ones, and none of the material read for this course puts the two countries' eggs side by side, so this course cannot tell you which supply is safer, and it does not suggest one country's advice is too careful or too relaxed.

If you live somewhere else, follow your own country's food safety regulator, as lesson 4 said. These two are shown because both were read.

Emulsions: oil held apart in water

Now the yolk's other job. Pour oil into water and stir, and for a moment the oil breaks into drops. Stop stirring and the drops find each other, merge and float to the top. Oil and water do not mix.

An emulsion is a way of making them stay mixed for a while. The American Egg Board quotes the definition from the magazine Food Technology: a "temporarily stable mixture of immiscible fluids, such as oil and water, achieved by finely dividing one phase into very small droplets."¹⁴ Immiscible means they won't mix on their own. In mayonnaise the oil is broken into droplets and the water, from the yolk and the lemon juice or vinegar, is the liquid they sit in.

Small droplets alone aren't enough, because droplets that touch will merge. Something has to coat each one and keep it from joining its neighbours. That is what yolk does, and the sources read for this course describe it in two ways that fit together:

• The Egg Board credits lecithin, a molecule in the yolk with "two ends, one hydrophobic and one hydrophilic": one end sits happily in oil, the other in water, so it settles on the boundary between them. That lowers the energy needed to make droplets, and the coating "acts as a barrier to prevent the droplets from joining back together".¹⁴
• Marc Anton, a researcher at France's national agricultural research institute, in a review of his field's work, credits mostly the yolk's low-density lipoproteins, tiny particles of fat wrapped in proteins and phospholipids (lecithin is one). When they reach the surface of an oil droplet they spread out, and the proteins and phospholipids form a film that both lowers the tension at the surface and gives "resistance to the rupture".¹⁵

Either way, the picture a cook needs is the same: every oil droplet is wrapped in a thin film of yolk material, and the film keeps it apart from the others. Anton adds a note worth knowing: yolk "is still used empirically and physical properties of yolk emulsions are not entirely controlled."¹⁵ Cooks know how to make mayonnaise work better than scientists can fully explain why.

The Egg Board gives a second reason yolk helps. It is thick, and "Egg yolks provide a viscous, continuous phase. This promotes stability in emulsions because it prevents the dispersed oil droplets from moving around and gathering, or coalescing."¹⁴ Droplets that cannot move easily can't find each other.

Why mayonnaise breaks

Anton describes three ways an emulsion can fail, and the difference between them is what matters in a kitchen. Droplets can clump together (flocculation) or drift up and gather at the top (creaming), and both of those "are reversible phenomena which can be avoided by a simple agitation of the emulsion". Or the droplets can merge, which he calls coalescence: "the irreversible fusion of oil droplets due to the rupture of the interfacial film created by emulsifying agents. This phenomenon leads to a complete destruction of the emulsion."¹⁵

A mayonnaise that has separated into a greasy, runny liquid has coalesced. Its droplets have run together, and no amount of whisking the broken sauce will re-wrap them.

The usual cause is the one the Egg Board names: "oil must be added slowly to water so that the lecithin within the egg yolk can thoroughly coat the small droplets."¹⁴ At the start of a mayonnaise there's very little yolk-and-water base and no emulsion yet. Pour oil in fast and it arrives as a pool, faster than your whisk can break it into droplets and faster than the yolk can coat them. Add it a few drops at a time and each drop is broken up and coated before the next arrives. Once the sauce has thickened, there's an emulsion to whisk new oil into, and you can pour faster, in a thin stream.

Two causes this course has not found a source for, and so only names: cooks also blame too much oil for the amount of water in the base, and ingredients at very different temperatures. The practice below lets you test the first cause, speed, which is the one the sources support.

Making mayonnaise, and saving one

America's Test Kitchen (ATK) publishes a mayonnaise recipe that happens to solve the US raw-egg problem, so it's a good one to follow in either country.

Its ingredients: 3 tablespoons of water (about 45 ml), 2 large egg yolks, 4 teaspoons of lemon juice (about 20 ml), 1½ cups of vegetable oil (about 355 ml), ¾ teaspoon of table salt, ½ teaspoon of Dijon mustard and ¼ teaspoon of sugar.¹⁶ Look at the proportions first. Oil is by far the largest ingredient: about 355 ml of it, against about 65 ml of water and lemon juice and two yolks. The base holds several times its own volume of oil, because every drop of it is wrapped and held apart. The lemon is lesson 3's acid: the "tart contrast" Nosrat described against sweetness, used here, as lesson 3 extended it, against richness, so the sauce doesn't taste heavy.

The method, step by step, with the reason for each:

1. Heat the yolks in liquid. Stir the water, yolks and lemon juice together, then microwave, stirring gently every 10 seconds, "until mixture thickens slightly and registers 160 to 165 degrees", which ATK says takes 1 to 2 minutes.¹⁶ That is 71 to 74°C, and it meets FSIS's rule for raw-egg recipes, heating the eggs "in a liquid form" to 160°F.⁵ ATK says that "Mixing the yolks with water and lemon juice kept the base of our mayo fluid even though it had been heated."¹⁶ By the ranges earlier in this lesson, a yolk heated on its own to that temperature would set. Neither ATK nor any other source read here explains why the diluted mixture doesn't, so take that as ATK's tested result.
2. Start the emulsion by hand, with a little oil. Immediately whisk in ¼ cup (about 60 ml) of the oil, with the salt, mustard and sugar. In ATK's words, the oil "cooled it and prevented it from thickening. At the same time, whisking broke the oil into tiny droplets, the critical starting point for any mayo."¹⁶ That first quarter-cup goes in at once, which looks like the mistake this lesson warns against. ATK doesn't say why it works, but this base is unusually big, about 100 ml of water, lemon juice and yolk, so the first 60 ml is less oil than base. This course's reading is that the drops-at-a-time rule is for when the oil would outweigh what's already in the bowl, and ATK slows to a drizzle from here on.
3. Add the rest slowly. ATK strains the base into a food processor, then, with the machine running, drizzles in the remaining 1¼ cups (about 295 ml) of oil "in thin stream, about 2 minutes."¹⁶ That's about 150 ml a minute: a thin, steady stream rather than a pour, going into a base that is already an emulsion.

ATK says this version keeps in the fridge for up to a month "because it's made with pasteurized egg yolks".¹⁶ The month is ATK's figure for its own recipe. None of the sources read for this course gives a keeping time for mayonnaise made with raw yolks, so if you make that kind, make a small batch, keep it cold, and use it soon.

By hand, in a bowl, the method is the same idea without the machine. Whisk the yolk with a little of the water or lemon juice, then add oil a few drops at a time, whisking all the while, until the sauce turns thick and pale. Only then move to a thin stream. If your arm tires, stop adding oil while you rest; the emulsion will not break while you're not pouring.

The one that splits

Say you've made a mayonnaise by hand, it's thick and glossy, and you tip in the last third of the oil at once because you're in a hurry. The whisk slips, the sauce goes thin and shiny, oil pools at the edges, and a minute later it is a runny yellow liquid with oil on top.

Diagnose it first. The oil went in faster than it could be broken up and coated. Droplets merged, the films around them ruptured, and in Anton's terms the emulsion coalesced, which is "irreversible".¹⁵ Whisking the broken sauce harder won't help, because the droplets have nothing new to hold them apart.

So you rebuild from a fresh base and feed the broken sauce into it as though it were the oil. ATK's fix: "Place 4 teaspoons water in bowl and, while whisking vigorously, very slowly drizzle in about ½ cup mayonnaise mixture (consistency should resemble heavy cream)." Then it goes into the food processor and the rest of the broken sauce is drizzled in slowly. ATK warns the result will be "slightly looser than unbroken mayonnaise but still thick and creamy."¹⁷ Half a cup is about 120 ml, and the 4 teaspoons of water about 20 ml.

Many cooks start the rescue from a fresh yolk instead of water, on the same logic: a new base with plenty of emulsifier, and the broken sauce added slowly. This course has not read a source that tests it against ATK's water method, so it is offered as common practice. If you're in the US and using the rescue on a mayonnaise you'll serve, remember that a fresh raw yolk brings back the raw-egg question, so use a pasteurised egg or heat the yolk with a little water first.

The same mayonnaise, for a pregnant guest

Now the dinner. You're making mayonnaise for a meal where one guest is pregnant. What you do depends on where you are.

• In the US, FSIS advises everyone against homemade mayonnaise made with eggs that aren't thoroughly cooked, and names pregnant women among those "particularly vulnerable".⁵ You have two routes: buy pasteurised eggs in the shell, or use the heated-yolk method above, which brings the yolks to 160°F (71°C) in liquid before any oil goes in. Either way the whole table can eat it.
• In the UK, the FSA says pregnant people can eat raw or lightly cooked hen eggs with the British Lion mark or from the Laid in Britain scheme.¹⁰ Make it with those eggs and raw yolks. If your eggs are from somewhere else, or they're duck eggs, the stricter rule applies and you'd heat the yolks or use pasteurised egg.¹²
• In either country, if the guest is severely immunocompromised, neither regulator's general advice covers them: ask what their doctor has told them.¹²

The same sauce, made safely both ways, by two different routes. That is what lesson 4's side-by-side table looks like when it reaches your kitchen.

A warm cousin: hollandaise

Hollandaise is an emulsion of melted butter in egg yolk, made warm. It breaks in two directions, and both follow from this lesson. Too hot, and the yolk proteins begin to set, which is the scrambling from the first half of this lesson happening inside the sauce. Too cold, and the butter itself firms up and stops flowing as droplets. So hollandaise is made over gentle heat and kept warm, not hot. This course hasn't read a source that tests either break, so take this as the usual kitchen account, reasoned from the setting temperatures earlier in this lesson, and it gives no temperatures for the sauce because it has read none. FSIS lists "Hollandaise sauce" among the dishes its raw-egg advice covers, so in the US the same pasteurised-egg rule applies.⁵

What people get wrong

"If an egg floats, it's gone bad." It's old, which is a different thing. The float test measures the air cell, which grows with age. The FSA says it "assesses age, not safety", and FSIS says to crack it and check it.¹⁰⁵ An egg that sinks can still carry Salmonella.

"The green ring means the egg was bad." It means the egg was overcooked, or cooled slowly, or cooked in water high in iron. It's iron and sulphur reacting at the yolk's surface, and both FSIS and the University of Nebraska say it is safe to eat.⁵⁶ Cool the eggs in cold water to prevent it.

"Wash eggs before you use them." Do not. FSIS says washing at home "increases the risk of contamination", because water can be drawn in through the shell.⁵ US eggs are already washed at the plant under controlled conditions.

"High heat cooks eggs faster, so it's better." It gets the outside there first and past it. The white next to the heat overshoots its setting temperatures while the yolk or the centre catches up, and you get a rubbery edge and an underdone middle. Gentle heat gives the inside time.

"A clean, uncracked egg from the fridge is safe raw." Not by US guidance: Salmonella can get into the egg before the shell forms, so clean and uncracked isn't enough.⁵ The UK's exception is about specific schemes' eggs, not about how clean an egg looks.¹⁰

"A broken mayonnaise just needs more whisking." Once the droplets have merged, the film around them has gone, and the break is irreversible.¹⁵ Start a fresh base and add the broken sauce to it slowly.

Practice

Connections

Lesson 2 gave you the idea this whole lesson runs on: heat comes in from the surface, the centre is last, and a gentle source gives the inside time to catch up. A boiled egg is that lesson's thick piece with a shell on it. Lesson 3's acid is the lemon in the mayonnaise, doing the job lesson 3 gave it against richness. Lesson 4's time plus temperature is behind every egg rule here, from the Food Code's 15 seconds at 145°F to FSIS's 160°F for raw-egg recipes, and lesson 4's two-country table is where the runny-egg row came from.

Lesson 6 makes a pan sauce and finishes it with cold butter, and that is an emulsion too, one that breaks if it boils, which lesson 6 explains. Lesson 7 roasts meat, and the carryover this lesson described, a hot egg still cooking after it leaves the water, is what lesson 7 measures in a roast, with proteins setting at their own temperatures just as the white and yolk do here. Lesson 10 comes back to emulsions with vinaigrette.

Go deeper

• USDA FSIS, "Shell Eggs from Farm to Table". Read in full for this course. The US regulator's long page on eggs: how Salmonella gets in, grades, dates, the float test, the green ring, peeling, and a storage chart. The best single page for the US rules.
• America's Test Kitchen, "How to Fix Failed Mayo". Read in full. Two paragraphs, and the rescue method this lesson uses, with the reason a food processor batch sometimes fails.
• Marc Anton, "Recent advances concerning the functional properties of egg yolk low-density lipoproteins". Read in full. Eight pages by a researcher who studies how yolk holds an emulsion together. Technical in the middle, but the first page and the definitions of creaming, flocculation and coalescence are clear, and it is candid about what is not yet known.
• Jacques Pépin's KQED technique videos. The playlist the poaching video comes from, with his knife, vinaigrette and chicken videos. The titles were checked for this course; the videos weren't watched.

Sources

1. American Egg Board, "Coagulation/Thickening", REAL Egg Functionality, https://www.incredibleegg.org/professionals/manufacturers/real-egg-functionality/coagulation-thickening/ , page copyright 2023 . Read level: full, directly. The US egg industry's promotion board, writing for food manufacturers; it cites Stadelman and Cotterill, Egg Science and Technology (1995), which was not read. Supports: the folded-protein description, the three-dimensional network, the white, yolk and whole-egg ranges, "a number of variables", and starch slowing coagulation in custard.
2. Egg Safety Center, "What is the safe temperature to cook eggs?", https://eggsafety.org/faq/what-is-the-best-temperature-to-cook-an-egg/ . Read level: full, directly. The page says the Center represents commercial egg producers. Supports: the same coagulation ranges; the 12, 9 and 15 minute hard-cooking method; poached eggs about 5 minutes in simmering water; the doneness wording for fried, poached and scrambled eggs (its table groups scrambled with fried) and for omelettes and frittatas. Rechecked at Stage 4 against the live page, which corrected the research file's attribution of the omelette wording to scrambled eggs.
3. Institute of Food Science and Technology, "Protein: coagulation", Love Food Love Science teaching resources, https://www.ifst.org/lovefoodlovescience/resources/protein-coagulation . Read level: full, directly. A schools resource from the UK professional body. Supports: 60°C, 65°C and 70°C, and "Coagulation is irreversible".
4. Jian Kuang, Pascaline Hamon, Valérie Lechevalier and Rémi Saurel, "Thermal Behavior of Pea and Egg White Protein Mixtures", Foods 12(13), 2023, 2528, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10340197/ , CC BY . Read level: the egg white passages of the full text; the pea results were not read. Supports: ovalbumin about 54% and ovotransferrin about 12% of egg white protein; their measured peaks near 63°C and 76°C; "many studies" finding peaks around 65 and 80°C; gelling at about 60 and 75°C. The link from these laboratory figures to the texture of a cooked white is this course's inference, and the lesson says so where it's made.
5. USDA Food Safety and Inspection Service, "Shell Eggs from Farm to Table", last updated 20 November 2024, read through the Internet Archive's capture of 29 August 2026 . Read level: full. Supports: Salmonella Enteritidis in clean, uncracked eggs and how it gets in; the carton statement; the raw-egg foods everyone is advised against and the vulnerable groups; pasteurised shell eggs and why they can't be made at home; the 160°F method for raw-egg recipes; the FDA Egg Safety Rule; grades, thinner whites with age, and the best eggs for poaching; sweating and 2 hours out of the fridge; coldest part, not the door; not washing eggs; cracks; hard-cooked eggs within 2 hours and a week; albumen pH and peeling; the green ring and the greenish cast on scrambled eggs; the float test; "Scrambled eggs should not be runny."
6. Alice Henneman, "How to Avoid a Green Ring on Hard-Boiled Egg Yolks", University of Nebraska-Lincoln Extension, reviewed and updated 2024, https://food.unl.edu/how-avoid-green-ring-hard-boiled-egg-yolks/ . Read level: full, directly, on recheck. Supports: the ferrous sulphide explanation, "unattractive, but not harmful", iron in the water, and cooling in cold or iced water.
7. Julie Garden-Robinson, "Prairie Fare: Are Runny Eggs Safe to Eat?", NDSU Extension, 7 April 2011, https://www.ag.ndsu.edu/news/columns/prairie-fare/prairie-fare-are-runny-eggs-safe-to-eat/ . Read level: full, directly. Supports: the USDA recipe's 15-minute simmer and cold rinse. The column's coagulation figures repeat the Egg Safety Center's, so it isn't cited for them.
8. foodsafety.gov, "Cook to a Safe Minimum Internal Temperature" (last reviewed 21 November 2024) and "4 Steps to Food Safety", read through 2026 Internet Archive captures . Read level: full. Supports: "Cook until yolk and white are firm"; egg dishes to 160°F (71°C); eggs "in their original carton", "not in the door."
9. USDA FSIS, "Washing Food: Does it Promote Food Safety?", last updated 7 February 2024, read through the Internet Archive . Read level: full. Supports: commercial washing removes the shell's natural coating, replaced with mineral oil, and eggs from the shop are not to be washed.
10. Food Standards Agency, "Home food fact checker", GOV.UK, first published 2 June 2020, updated 21 August 2026, https://www.gov.uk/government/publications/home-food-fact-checker . Read level: full. Supports: the groups who "can now safely eat raw or lightly cooked hen eggs" with the British Lion mark or from Laid in Britain; the severely immunocompromised exception; the float test "assesses age, not safety".
11. NHS, "Foods to avoid in pregnancy", last reviewed 15 June 2026, https://www.nhs.uk/pregnancy/keeping-well/foods-to-avoid/ . Read level: full, directly. Supports: British Lion or Laid in Britain eggs "can be eaten raw, partially cooked (runny yolk), or well-cooked", and other hen eggs "should only be eaten well-cooked".
12. Food Standards Agency, "New advice on eating runny eggs", food.gov.uk, 11 October 2017, read through the Internet Archive's capture of 17 October 2017, https://web.archive.org/web/20171017232923/https://www.food.gov.uk/news-updates/news/2017/16597/new-advice-on-eating-runny-eggs ; also reproduced by the Institute of Food Science and Technology, https://www.ifst.org/news/new-advice-eating-runny-eggs-fsa-0 . Read level: full, directly, both copies; the text matches. Supports: the ACMSF expert group and its July 2016 report; salmonella "dramatically reduced"; the Lion scheme's measures, including vaccinating hens; "More than 90% of UK eggs" when the advice changed; the severely immunocompromised exception; non-Lion, non-hen and imported eggs cooked thoroughly for vulnerable groups; storing eggs "in a cool dry place such as the fridge".
13. US Food and Drug Administration, Food Code 2026, § 3-401.11 and Annex 3, https://www.fda.gov/media/194741/download . Read level: the sections cited, searched in the full PDF. Supports: raw eggs broken for immediate service to "63°C (145°F) or above for 15 seconds"; the 3-log reduction of Salmonella Enteritidis that the Annex attributes to 15 seconds at that temperature; raw or undercooked eggs on consumer request with an advisory, not for highly susceptible populations.
14. American Egg Board, "Emulsification", REAL Egg Functionality, https://www.incredibleegg.org/professionals/manufacturers/real-egg-functionality/emulsification/ , page copyright 2023 . Read level: full, directly. Supports: the Food Technology definition of an emulsion; lecithin's two ends and lowered interfacial tension; the coating as a barrier; the viscous continuous phase; oil added slowly so the droplets can be coated.
15. Marc Anton, "Recent advances concerning the functional properties of egg yolk low-density lipoproteins", INRA Nantes, World's Poultry Science Association conference paper, https://www.cabi.org/Uploads/animal-science/worlds-poultry-science-association/WPSA-italy-2006/10903.pdf . Read level: full, directly. Supports: yolk's emulsifying properties "principally attributed to its LDL"; the film of proteins and phospholipids and its "resistance to the rupture"; "still used empirically"; flocculation and creaming as reversible and coalescence as the irreversible fusion that destroys an emulsion.
16. Lan Lam, "Make-Ahead Homemade Mayonnaise", America's Test Kitchen, 5 January 2020, https://www.americastestkitchen.com/recipes/12375 . Read level: full, directly, the public part of the page. Supports: the ingredients and quantities; heating the yolk base to 160 to 165°F in 1 to 2 minutes; the base kept fluid by water and lemon; oil cooling the base and breaking into droplets; the slow drizzle over about 2 minutes; one month in the fridge, which is ATK's claim for its recipe.
17. America's Test Kitchen, "How to Fix Failed Mayo", https://www.americastestkitchen.com/how_tos/13363-how-to-fix-broken-mayo . Read level: full, directly. Supports: 4 teaspoons of water, about ½ cup of the broken mixture drizzled in very slowly, then the rest, and the slightly looser result.
18. Advisory Committee on the Microbiological Safety of Food, Ad Hoc Group on Eggs, "An update on the microbiological risk from shell eggs and their products", July 2016, read through the Internet Archive's capture of 20 December 2016, https://web.archive.org/web/20161220073347/https://www.food.gov.uk/sites/default/files/acmsf-egg-reportv1.pdf . Read level: the overall risk assessment and key recommendation (pages 8 and 9) and paragraph 5.47 on egg washing, searched in the full text; the rest of the report was not read. Supports: "VERY LOW" risk for Lion eggs "or under demonstrably-equivalent comprehensive schemes" and "LOW" for other shell eggs; such eggs "can be served raw or lightly cooked to all groups in society, including those that are more vulnerable"; washing Class A table eggs "is not permitted in the UK".

The two embedded videos, Jacques Pépin's "How To Properly Poach An Egg" (KQED Food) and "Learn Jacques Pépin's famous omelet techniques" (American Masters, PBS), were checked for title, channel, length and description only . Nothing in the lesson is attributed to what they show.