There's at least two things people say about mashed potatoes that are straight-up myths.
They're both so illogical on their face that I can't believe either is widely believed,
but believe it. Myth number one: You have to salt the boil water for the potatoes. You can't just
salt the mash at the end. You've got to salt the water up front. This makes no sense. It's a myth
and I'm going to prove it. I'll salt the water basically the way I salt water for pasta. No, the
salt doesn't really make the water boil hotter. It just offers a lot of little irregularities around
which bubbles can form — bubble nucleation sites. That's why the water kind of explodes when you
first put the salt in. Once the salt is dissolved, it does raise the boiling point of water, but to a
totally insignificant extent at any reasonable level of saltiness when it comes to cooking.
It boils a tiny fraction of a degree hotter. That's not a good reason to salt the boil water.
In fairness, I think most people who advocate salting the boil water for potatoes say that
that's really all about flavor — seasoning, making sure that the potatoes are going to be properly
seasoned. That is what we are testing. On another batch I'm going to use no salt in the water.
250 grams of Yukon Gold potatoes, just like the salted batch, boil them until very fork tender,
which is what I think you generally want to do for mashed potatoes. Drain. Brine-boiled potatoes are
on the right. Two tablespoons of butter into each one. Two tablespoons of milk into each,
and a pinch of salt for the batch that we did not season at the boiling phase. Mash
them both up smooth and they taste exactly the same. That should really come as no surprise.
Mash is a homogenous or near-homogenous product. It does not matter when or where we add in the
salt when it's all going to get mixed up in the end. I thought that it might be possible that
the salt could affect the starch on a chemical level, maybe change the texture in some way,
but I perceived absolutely no textural difference or taste difference. Though actually, I lied when
I said these taste exactly alike. The one that we didn't season up front actually needs a little
more salt to be as salty as the other one, and that actually makes this batch superior. When
you season at the end, you can do it to taste. Some things you have to season up front. Like,
you can't stir salt into an already baked loaf of bread. You have to put salt into the dough. So
you have to kind of guess at that stage how much salt you're going to want at the end. With mash,
there's no reason to guess. Just season at the end, and then you can do it entirely to
taste. Stir in a little bit of salt, taste it. If you want a little more,
stir in a little more. Plus, seasoning at the end is less wasteful. When you season the boil water,
a lot of the salt goes down the drain. OK, mash potato myth number two: People say
you have to drain the potatoes really thoroughly and then let them steam off. Get all the water out
of the pot that you can or your mash is going to be watery. This is also so illogical on its
face that I can't believe any part of me ever believed it, but believe it. I'm going to prove
to you that people are making mash sound way more complicated than it is. It's almost as though we
can't accept how effortlessly delicious this food is — as effortlessly delicious as HelloFresh,
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for 16 free meals. Thank you, HelloFresh. Anyway, myth number two: You have to thoroughly
drain and then steam off your potatoes, otherwise they're going to be water-logged. This is a myth;
I'm going to show you. Here's some thoroughly drained boiled potato chunks. A big knob of butter
as the Brits would say, a pinch of salt, mash, and here's what mashed dry potatoes look like:
super stiff. Even with all that butter and the mouth feel is unsurprisingly dry. Mashed
potatoes without water are bad. They're texturally dry. People generally deal with
this one of two ways. They might massively increase the amount of fat that they stir
in. Like I've seen people go as high as 50% butter by weight, which is completely insane.
Or they add water back into the potatoes, usually in the form of milk. Modern cow's milk is about
87% water. The remaining 13% is fats and sugars and proteins that taste delicious,
but they do not taste very strong, at least not when diluted into a whole pot of potatoes. At
best, milk gets you a very subtle dairy flavor that you'd probably get from the butter anyways.
That doesn't stop me from using milk. I have little kids, so I always have milk in the house,
and if I need to add some water to something and milk would be an appropriate flavor, I'll use
a little bit of milk, even if it doesn't make a huge difference. But let's taste the alternative.
These potatoes I will drain thoroughly, but I'll catch the boil water in a little glass.
Two tablespoons of butter as before, pinch of salt as before, and instead of two tablespoons of milk,
I'll do two tablespoons of the boil water. So it's as if I didn't drain the potatoes very thoroughly,
but it's the exact same amount of liquids, so I'm putting this batch on totally equal footing
with the batch I made with milk. How does it taste? Holy crap, that actually tastes better.
I was not ready for this. I was ready to tell you that it doesn't matter that whether you use
milk or whether you use just a little bit of the boil water — the amount of non-water ingredients
in both liquids is just tiny, so it doesn't matter, but it actually kind of matters. It
just doesn't matter in the way people think. The batch I made with the boil water tastes
noticeably more potato-y, and I notice no lack of dairy flavor cause I've got the butter in there.
I just noticed the addition of potato flavor. It's a subtle difference, but I really like it.
There is one good reason to somewhat thoroughly drain the potatoes,
and it's the same reason why you don't season the mash until the very end. Whenever possible,
defer decisions until the end. Wait until you can taste the finished product to decide
exactly how much water or water-based liquid you want in there. But I've got a pretty good
eye for how much liquid I want in my potatoes, so going forward, I think I'm just going to not
drain them very thoroughly, same thing I do with pasta when I want some pasta water in my sauce.
Hey, this reminds me. Some people say that you can boost the flavor of your boil water
by including the skins that you peeled. Usually I only bother peeling floury potatoes, like these
baking potatoes. Their skins have a pretty gross wet-cardboard texture when boiled. I'll stuff
those skins into some cheese cloth and tie it up, drop it into the water like a stock cube,
fish it out when the spuds are done, drain and finish the mash per usual. That tastes
identical to this same batch that I made with the same potatoes and no skins in the water. I
noticed no difference at all. Oh, well. But I wonder, could you get the best of
both worlds by boiling the potatoes in milk? This would get us the concentrated potato flavor and
the extra dairy flavor, right? People do this, but it is kind of a pain. When milk cooks, the
proteins coagulate, it thickens, and you raise the surface tension considerably, so it forms bigger,
more stable steam bubbles. The pot will boil over if you're not careful. You either have to
stir it continuously to break the bubbles, or you have to turn the heat down and cook everything a
little slower. Milk also has lots of sugar that can stick to the bottom of the pan and burn,
so you have to stir for that reason as well. Potatoes look about done. I'll drain the
excess milk away — kind of wasteful, that is. The resulting mash has a really strong dairy flavor,
unsurprisingly. Very nice flavor, but the texture is like a little grainy. I could feel those
cooked, clotted milk solids on the tongue. Didn't really like that texture. Now, I kind of think you
could probably solve all of these problems by simply boiling the potatoes in water per usual,
and then if you want that extra dairy flavor, mix in some powdered milk at the end.
I wonder if the potatoes would taste water-logged if we massively over-boiled them. Lots of recipes
warn against doing that. These I've boiled nearly twice as long as I normally would.
They're really starting to fall apart. I'm definitely getting a lot of cooking
loss — that's quality potato that I'm simply dissolving into the boil water, that I'm mostly
draining away. Cooking loss is wasteful, but when I finish these potatoes as usual,
they taste totally fine. They taste just like all the other batches. Waste is bad, but I'd say,
when in doubt, over-boil instead of under-boiling. If you under-boil, you end up with these little
lumps that are just too hard to ever mash up. Last thing I want to test: What happens if
you just barely simmer the potatoes for a long time, rather than holding them at a rolling boil
for less time? This is something I think I first heard about from Heston Blumenthal. I've read many
conflicting scientific explanations about what's going on here. Some people say we're activating
enzymes that break down the starch. Some say we're breaking down the pectin. Some say we're
hydrating the starch really thoroughly. Some say we're preventing bonds from forming between cells
that would normally form at higher temperatures. Maybe it's all of the above, but regardless,
that really does produce the smoothest mash you've ever tasted. Very fine texture, very creamy.
But again, it's not a huge difference. Mash is super easy. It's the perfect side dish,
apart from its nutritional content. All you've got to do is just boil some potatoes until they're
soft. Mix in some stuff to taste until you like it. You can make it way in advance, and it just
sits around and doesn't degrade in quality at all as you finish the rest of the meal. Mash is great.
That said, I wonder if we couldn't maybe combine some of the things
we learned today into kind of one ultimate mashed potato recipe...