UKC

I'm a virologist and don't really do chemistry, so plain language answers please!

I'm curious about what is happening when you cook something.  I think I understand the denaturing of proteins and breaking of collagen.  Also cell wall rupture.

I suppose I'm particualrly interested in why crisp fried onions require oil (or so much oil).  Is it that the dehydrating, and even the caremalising, could take place in a dry oven, but that oil's high smoke point enables full surface heating at higher temperature than an oven?  Or is the oil doing more than this?  Oils are also good flavour vectors - so would a flash-roasted onion from a 400oC cruclible be less flavoursome?

You rumbled me.  Basically I want crispy onion bits that aren't 50% saturates!

Look up Harold mcgee, on food and cooking - browning reaction.

man up. Less than 50% saturates is for amateurs.

really you should be aiming higher-  80%+ for any self respecting fried food aficionado

and to get into the big time, you need to look to how they do it in Glasgow- number 2 is at least 150% saturates, probably...

https://www.glasgowlive.co.uk/news/glasgow-news/five-glaswegian-chip-shop-d...

If I’m browning my meat and two veg, I always ask the Mrs if she prefers oil. She’s an anti virologist and prefers it wrapped. 

Good question.  I have no idea.  Browning onions for a curry is one of the few bits of cooking that I find to be a mysterious art form and not reducible to a simple protocol.  I think it’s a quantum uncertainty thing - they always burn the moment I stop looking.

I am a geneticist / developmental biologist (actually also with a background in virology, my first paper was on new world monkey herpes viruses!). So my organic chemistry has been a while, but anyway, here goes:

The main taste producing mechanism in frying is the Maillard reaction, whereby an amino acid reacts with a reducing sugar subunits (usually not free) by forming an intermediate Schiff base. After multiple rearrangements you end up with a whole zoo of products, including maltol (the compound also responsible for the smell of roasted bread) and norfuraneol (caramel notes in fried meat).

The protein denaturing and destruction of cell membranes also happens during cooking, but the Maillard products are distinctive for frying as they are not generated in the presence of water.

No guarantees, though. As I said, it has been a while...

CB

edit: forget the saturates, when you fry you will necessarily also produce nasties like formaldehyde and acrylamide. You can reduce that, at least somewhat, by using a thermostable frying oil.

Nice - thank you!

My first paper was also on herpes, but human - mechanism of ACV-resistance and consequent attenuation of pathogenicity.

*Why* aren't the Maillard products generated in the presence of, say, super-heated steam?

Or is the deal that all the water from the onion (say) has to be driven off before the base material can heat enough to generate these compounds?  What if I had steam at 1000oC and frassed it?

Do you mean a high burn point like canola?

I'm an inorganic chemistry, but I can still point you in the right direction:

https://en.m.wikipedia.org/wiki/Maillard_reaction

As for the oil, I think it's about holding the temperature. Without oil you would caramelize the surface, so the oil provides in-stock and promotes the maillard reaction. The type of oil regulates the temp, unless you burn the oil. So olive works well for slow, rape seed for higher, lard for the top temp.

Onions are tricky. You can cook them low and slow, they go sticky and sweet - I do this for onion soup or curry base. You can up it a bit and get browning flavour used for in casseroles, or actually burn them and get a bitter note - not sure any desired recipes require this.

What, nay butter?

As a 'non-cook' who's being cooking for 40 years, not very good at all, I find rape seed oil (I only discovered it about 3 years ago) really excellent. Very clean, doesn't burn at all easily. 

I've not looked back since I started doing them on the hottest burner on full, but with constant attention. A lot of the flavour compounds that form on browning onions are apparently water soluble, so if you fry the onions hard briefly, then stir a splash of water in, you redistribute a lot of the colour and flavour throughout the onions. Let the water boil off and then repeat until the onions are at the desired brown-ness, and you'll end up with evenly deeply browned soft onions in 15 minutes that otherwise might take 35-45 minutes.

See: https://www.seriouseats.com/recipes/2012/08/quick-caramelized-onions-recipe... Don't follow the tip to add baking soda and sugar or you'll get mush though.

I seem to remember reading something about the temperature of the oil affecting its absorption into the food being fried - hotter oil being less absorbed, I think. Maybe because the food is cooked faster so there's less time for the fat to replace the water that's being driven out 

Certainly with batter you need it high to form that hard crust. Unused to remove battered fish batter as a kid, and the fish was always moist. Moved north and in-land and the batter is awful and the fish greasy. Funny that in a country where no where is that far from the sea, you get crap fish and chips as soon as you're not on the coast.

Mmm tempura haddock is where its at

Not sure, but I would assume that the presence of lots of water shifts the equilibrium of the initial step of the Maillard reaction (formation of the Schiff base by sequential elimination of H2O and CO2) towards the educts.

CB

Can anyone suggest good books or resources for *this* sort of knowledge?

The classic has already been mentioned - Harold McGee's 'On food and cooking' but that was published some time ago (1980s?) so maybe there's something more recent

Might not be sciencey enough for you, but I like this one - https://www.amazon.co.uk/Food-Lab-Cooking-Through-Science/dp/0393081087

By the guy behind the serious eats site.

This seems a pretty good book on culinary science, from the brief flick-through I've had:

https://www.hive.co.uk/Product/J-Kenji-Lopez-Alt/The-Food-Lab--Better-Home-...

Haha! Beat you to it! I should've added that I have the book and really like it.

Serious Eats is a great website and I've picked up loads of great tips from it. The only recipe that I've tried from there that misses the mark is their method for roast potatoes, but to be fair it is an American website and roasties are pretty much a national obsession here.

I was going to write a science and cooking book years ago. In fact I set up my blog and twitter accounts on the basis of chemistry and cooking, but sadly I don't have the time. Maybe when I retire in 15+ years I'll consider it.

Ultimately though, people cook to taste not to specification. So if you like the bitterness of burnt garlic you put it in at the start on a hot pan with rapeseed, if you want more mellow you lower the temp and cook slower in olive oil. Or you can poach your meat in garlic broth before adding it into a curry or casserole. You don't need the science to avoid the mistakes.

I've noticed that if you don't use enough oil, the onions burn rather than caramelise. Maybe the oil is acting as a barrier that stops oxygen getting to the food. Also if you don't have a lot of onions (base of pan completely covered), they tend to burn.

Only because the water prevents the temperature getting much over 100 C at atmospheric pressure, stick your onions in a pressure cooker and you can keep them soft, juicy and  yet still browned and delicious.

For crispy onions with less oil, the OP could try making them in the microwave or a fan oven.

This seriously has the potential to become a legendary UKC classic thread. I’ll be keeping an eye on it

Nah. No-one's mentioned a treadmill, Brexit or the conditions at Kinder Downfall yet....

In her later years my dear mother announced to the family that 'she was now frying onions in water'

- yes I was nonplussed too :o 

Objection, your honour! The gastro-chemical process is completely different, which is where the horrible taste of steam heated canteen food comes from: The onions may become brown, but that is where the similarity ends!

CB

I did say I wanted *CRISPY*.... so away with all these pressure-cooked/streamed/boiled ideas.

Can I get crispy without oil?  If not, why not?

This is what hasn't really been answered yet. Lots of Maillard reaction/ caramelisation answers which are all good but nothing to do with the crispiness.

Have you tried dry frying/ hot roasting/ blowtorching onions?

that have now

Maillard reactions are important in malting and brewing so can take place in the presence of water. 

They mostly occur while roasting the malt, to a much lesser extent in the wet. The first step is always an elimination reaction disfavoured by the presence of the product that is eliminated, here water. Simple equilibrium chemistry.

CB

The effects from wort boiling can still be noticeable, particularly if using lightly kilned malts.