Science of Food books

For everyone who came to my Bread, Brie and Booze talk at the British Science Festival, here’s the science of food books I recommended, plus the recipe for the instant homemade cheese that everyone seemed so fond of!

On Food and Cooking – McGee

The Chemistry of Food – T. P. Coultate

Culinary Reactions – Simon Quellen Field


1 pint milk, 2 tablespoons vinegar (I used distilled malt vinegar), 1/4 teaspoon salt. Mix all ingredients in a microwave-safe bowl or jug and microwave on full power for 4 minutes. Take out and stir and large clotted curds should form. Strain these out with a slotted spoon into a seive lined with several pieces of kitchen towel and drain. You will need to change the kitchen paper a couple of times, and gently pressing the cheese will get more liquid out of it.

Daily Science Factlet – the Perfect Cheese Toastie

Sometimes nothing will do but a crispy, savoury, oozy toastie. But which are the best cheeses to use? Well, science can help you out…

First of all, to get the gooey centre, you want a cheese (or combination of cheeses – let’s go all out here) that will give a ‘good melt’. There are some cheeses that would definitely not be good for this, particularly the acid-coagulated cheeses like paneer, ricotta and cottage cheese (see my post on why they don’t melt well).

The most important factor in melting is water content. High water content in the cheese dilutes the proteins that make it solid, meaning they are more weakly bonded together and so will flow past each other and melt at a lower temperature. Moist cheeses like fontina, gruyere and monterey jack are therefore good to provide the gooiness.

Watch out for using high fat cheeses – they are more likely to leak melted fat as the protein network breaks down with heat, and can make the toastie greasy. Though to be fair, that is often part of the enjoyment. It’s not a health food.

Now to stringiness. For some, another important aspect of a toastie. The reason a cheese goes stringy is that the little balls of milk protein (called casein micelles) in the cheese get linked up into long chains by calcium.

Cheeses tend to get less stringy with age. The first reason for this is that as a cheese ages, more and more lactose sugar is converted to lactic acid. Acid dissolves the calcium holding the micelles together, stopping them from forming stringy ropes and making them fall apart and flow more easily. The second reason is that as a cheese ages enzymes start to break down the micelles into small pieces that are too small to link up into chains.

So if you’re a string fan, then cheeses like emmental, mozzarella and young-ish cheddar are good. And if you prefer just a gooey centre, just use the moist cheeses above, and maybe an aged cheddar too.

Daily Science Factlet – Acid cheese

So, in the run up to my shows at the British Science Festival in September, I’m going to be pinging out exciting little facts all about the science of bread, cheese, alcohol and microbes, plus probably a few on the science and psychology of comfort food too.

To kick off, a post on acid coagulated cheeses. These include ones like cream cheese, paneer, many soft goats cheeses, and ricotta, which differ from cheeses like Cheddar, Parmesan and Roquefort in that they do not use rennet in their production. To explain the difference, let’s take a quick step back to look at milk, and why it curdles, and how acid and rennet do it differently.

Cows’ milk is around 3.5% protein by weight (most of it is water), which can be split into two types; caseins and whey proteins. Caseins make up roughly 80% of the protein in milk, and are found bound up with calcium ions in little hairy-looking balls called micelles (check out my expertly drawn picture). It’s these micelles that rennet acts on (but more on that later). Whey proteins are only about 20% of the protein content, but include types of proteins called immunoglobulins, which can cause allergic reactions. They’re very stable once heated, and are what stabilises the bubbles in the milk foam you get on your cappuccino in the morning.

Curdling milk to make cheese means allowing the proteins to clump together. Rennet does this because it contains an enzyme that strips the casein micelles of their negatively charged coatings, stopping them from repelling each other and making them able to get closer together and form curds. If just using rennet to make cheese, the whey proteins are left by the ‘whey’-side (sorry…), and are drained off. But they do get in on the act if acid is used to curdle the milk. Many of us have experienced that horrible moment when that slightly-old-but-probably-still-ok-to-make-tea milk curdles when you add it to the cup. This is because the tannins in tea act like acids, neutralising the negative charges on the micelles, plus dissolving the Calcium bridges holding them together, and also denaturing the whey proteins, making a horribly lumpy cuppa.

Using acid to curdle or coagulate milk allows all of the proteins to bind together into a much finer, closely linked structure than if rennet had been used. This means that when acid-coagulated cheeses are heated, the first thing to be lost is water, actually making the cheese harder. This is why paneer can be cooked in whole pieces in curries without falling apart, why cottage cheese doesn’t melt like cheddar on a baked potato, and why ricotta stays in tasty little blobs on pizzas or in lasagna, rather than spreading out like mozarella.

Daily Science Factlet – Useful Moulds

Gah! Only a week in, and already I’ve missed out a day. BAD ScienceSponge.

Well, to make up for it, today’s factlet is all about how Penicillium moulds are more than just those annoying patches of fuzzy mould on your week-old bread. Moulds in the Penicillium genus are soil dwelling, and responsible for most cases of food spoilage (along with Aspergillus). But as well as infecting plants, animals and occasionally immunocompromised people, they can in fact be rather useful.

Penicillium chrysogenum is the fungus that was found to produce an antibiotic substance by Alexander Fleming. It releases it in response to stress to compete against other microorganisms in the area. The substance was later developed by Howard Florey and others to produce Penicillin. This antibiotic and its derivatives kill bacteria by preventing them from strengthening their cell walls, and have saved countless lives.

A couple of the relatives of this fungus are very handy when it comes to cheesemaking. P. roqueforti and P. glaucum are both used to produce blue cheeses like Roquefort, Gorgonzola and Stilton. They are mixed into the milk early on and develop the blue veins and pungent flavour of these cheeses. And P. camemberti is sprayed onto the outside of Camembert and Brie cheeses and develops their characteristic white rind. (If you want to know a bit more about cheesemaking, you can watch the Scrapbook video podcast I made on it for the Naked Scientists.)

I’d still stay away from mouldy bread though…