They’re great for the kitchen, the cooking process is easier to manage and it yields more consistent results.
But, for the person eating them, they’re not quite as good as a perfectly poached egg.
The perfect poached egg has an egg white that is cooked hard, all of it, but the yolk is soft in the middle. Actually, the yolk has a delicate balance of almost hard on the outside, transitioning to soft in the middle. Soft enough that it will run out onto your toast but not freely run off the toast.
All subjective of course. If you like your eggs raw or boiled hard enough that they could bounce, then look away, this might not be for you.
The problem lies with the cooking temperature of the egg white vs the cooking temperature of the egg yolk. They’re different. I know this not from measuring or from research but just from eating 70 degree eggs. I honestly have not looked up the cooking temperatures of each but I will do so right after typingthis sentence.
I did two separate google searches:
Both searches return the same article as the top result: [Cooking Eggs Sous Vide](https://www.scienceofcooking.com/eggs/cooking-eggs-sous-vide.html. The article has just the info we need. These two sentenses sum it up:
The major protein of egg white, ovalbumin, makes up 54% of the white and doesn’t coagulate until the temperature reaches 80 °C. The yolk begins to thicken around 65 °C and sets around 70 °C.
The yolk proteins begin to thicken at 65 °C and set at 70 °C. Further heating to around 80–90 °C produces the crumbly texture typical of hard boiled eggs. (McGee, Science of Cooking, pp 85) .
So it’s easy to see that cooking an egg at 70 degrees for a longer (longer than standard poached egg times) time will give you a white that is runnier than the yolk.
Cooking an egg 70 degree style gives a relatively uniform temperature throughout, or at least the whole egg approaches that uniform temperature (70 degrees). But the yolk requires a lower temperature to coagulate so the yolk will begin coagulate more than the egg white.
If that were the goal then great, but I don’t think it is. I think the goal is an easier cooking procedure for the kitchen. It’s also perhaps trendy to put “70 degree egg” on your menu.
The main reason this 70 degree egg problem exists is that kitchen efficiency trumps customer experience and that’s a whole separate topic which I won’t go into here. Suffice to say that if you allow customer experience to trump kitchen efficiency (and we must be pragmatic with this – a business has to make money – but I don’t know of any restaurants that went out of business because they were poaching too many eggs) then you wind up poaching eggs instead of doing 70 degree eggs every time, simply becuase the customer experience is better.
Googling for some pictures: