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.

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Daily Science Factlet – crustacean colouration

Whilst chowing down on some prawns recently, someone asked me why it was that they were a blue-grey colour when raw, and a pink colour once cooked. Here’s why…

If you look closely at a raw prawn, you can see that the colouration isn’t even, but is distributed in small spots on their shell, and on the flesh underneath. The spots are made up of pigment-containing cells called chromatophores, that you can find in all kinds of organisms from bacteria to birds and plants to parrotfish. The combination of overlapping cells containing different coloured pigments gives the final colour of the organism (and making the chromatophores expand or contract is how octopus and cuttlefish are able to change their colour).

The key pigments involved in the blue-grey to red change in prawns (and lobsters) are the red astaxanthin (that also makes salmon and flamingos pink), and the blue crustacyanin. Crustacyanin is actually made up of several astaxanthin molecules tied up together with a protein molecule. In raw prawns and lobsters you have a combination of the red astaxanthin and the blue crustacyanin in the cells, giving a greyish blue.

But when you heat prawns up, the protein holding the crustacyanin together unravels, freeing up the astaxanthins. These are very heat tolerant, so just stay red on heating, making the cooked prawns look that appetising pink colour…

Daily Science Factlet – comfort food facts

Today’s factlet is more a little group of factlets really. Today I’ve been immersing myself in the world of food psychology; specifically the psychology of comfort food. Here’s some of the interesting little tid-bits I’ve found so far:

  • When people are sad they are more likely to indulge in ‘hedonic’ foods (e.g. M&Ms and popcorn) than when they are happy, in order to improve their mood.
  • But happy people are more likely to over-consume healthier ‘non-hedonic’ foods, in order to maintain their mood and to avoid later regretting eating something indulgent.
  • Men report preferring meal-type comfort foods like soup, pizza and pasta, but women report preferring snack-type comfort foods like crisps and chocolate. The researchers who carried out this study suggested that this could be because the men preferred foods that made them feel looked-after, and women found comfort in foods they didn’t have to spend a long time preparing (though I’m not really convinced by this as an argument in this age of higher gender equality in the kitchen)
  • Allowing ‘consumption norms’ like how much your friends are eating or only stopping eating once the plate is empty can lead to over eating.
  • Distractions like TV can increase consumption – so-called ‘mindless eating’, because they create patterns of eating behaviour that aren’t correlated with hunger

One thing I have noticed in doing this research is that the results of experiments done on participants who didn’t know what the experimenters were looking at don’t always agree with studies where people have volunteered information about their preferences and eating habits. It seems that people are often not aware of how their behaviour is changed by factors like mood and external cues.

This is a truly fascinating area – if you want to read more, I highly recommend Brian Wansink‘s website, and that of the Cornell University Food and Brand Lab. Both have great educational resources and tips for reducing your own ‘mindless eating’.

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 – Spicy Spices

A factlet about some of our most popular spicy spices used in cooking today – ginger, pepper and horseradish.

Ginger is a root related to the plants that provide us with cardamom and turmeric, and distantly related to the banana. The pungent spicy chemicals in ginger are called gingerols, which when dried become shogaols, which are much spicier.

The compounds that provide the spice in pepper (piperine) and chillies (capsaicin) are chemical relatives of gingerols. Pepper comes in black, white, green and pink (though ‘pink peppercorns’ are from a completely different plant), referring to different ways the raw berries have been treated.

Horseradish and wasabi are both relatives of the cabbage family, and their pungency is provided by a very different chemical – sinigrin. Used as a chemical defence in the plants, it is far more volatile than piperine, capsaicin or gingerol, which is why horseradish and wasabi irritates right up the back of the throat and nose and not just the tongue.

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…