Daily Science Factlet – watching yeast breathe

Big thanks to the Naked Scientists’ Kitchen Science website for providing me with the rough amounts to use.

Yeast are the tiny, single-celled relatives of mushrooms that we rely on to make bread and alcohol. When they gobble up sugars in flour or in fruit juice, in an environment with not much oxygen, they produce alcohol and carbon dioxide gas.

Glucose –> Ethanol + Carbon Dioxide

This gas is what makes dough rise and puffs up a loaf of bread, and is also what gets trapped in bottles of champagne, so that they fizz up when you pop the cork.

What you will need:

1 empty drinks bottle (500ml)

1/2 a sachet of dried yeast (about a teaspoon)

3 or 4 teaspoons of sugar

Warm water

1 balloon (blown up and let down a couple of times to stretch it)

What to do:

Pour the yeast and sugar into the bottle. Add warm water until the bottle is around half full (mine was a bit more than that). Screw on the lid and shake it around a bit to dissolve the sugar and disperse the yeast.  Take off the lid and stretch the balloon over the bottle opening. Leave it somewhere warm for about 20 minutes-half an hour.

You’ll see the balloon start to inflate and a thick layer of bubbly scum on the top of the water in the bottle. This is the yeast respiring! You can vary the experiment by comparing variables like the temperature of the water, the sugar source used etc.

And that’s it really. The video below is a speeded up version of the reason this whole experiment is worthwhile. I’ve removed the sound, so you can’t hear me giggling like a loon…

Daily Science Factlet – Which Wheat?

At a slight loss for what to write for today’s factlet this morning, I turned to twitter. Some nice questions on long distance travel and why vertebrates have four limbs came up (I may return to the vertebrate limb question at a later date), but @donalde suggested talking about the genetics of wheat. Seeing as that fits in nicely with my vague bread, cheese, alcohol and comfort food theme for the next couple of weeks, I thought I’d give it a go. I won’t be covering all of the 30,000-odd varieties of wheat, but just some of the most common, and interesting…

One of the first types of wheat to be cultivated by humans (around 10,000 years ago), that is still around today, is called einkorn (a.k.a. Triticum monococcum). In terms of its genetics, einkorn is like you and I – it’s diploid. This means it has two copies of each of its chromosomes in every cell. “So what?” you may say – well, the number of chromosomes gets important later. Domesticated einkorn isn’t found all that commonly any more, but is still used to make a porridge-like dish in parts of France.

The next type of wheat to mention is Triticum turgidum. This arose from a chance mating between a wild form of wheat, Triticum urartu and a type of goatgrass. The offspring of these two was a tetraploid form of wheat – with every cell containing four copies of each chromosome rather than the two copies of its diploid parents. This doubling up of the chromosomes, called polyploidy, was once thought to be more common in plants than in animals, though there is evidence to suggest that it could have played an important role in the evolution of both plants and animals. The tetraploid wheats still feature in our diets today – Durum wheat is used to make the characteristically yellow semolina flour, and to make pasta, and Emmer or Farro is used a bit like barley or rice in Italy.

Yet another chance mating, this time between a Triticum turgidum species and a wild goatgrass around 8,000 years ago, resulted in the hexaploid wheats that we most commonly use (all included in Triticum aestivum), with six copies of each chromosome in their cells. The extra chromosomes are thought to contribute to the versatility of these wheats, particularly their gluten proteins. The hexaploid wheats include T. aestivum aestivum, our common bread wheat, which itself comes in several varieties split up according to the strength of their gluten proteins, and the high-protein grain spelt (T. aestivum spelta). Genetic studies have suggested that European spelt may have arisen from a separate hybridisation of Emmer wheat and bread wheat, making it genetically distinct from Asian spelt, which was the result of T. turgidum hybridising with goatgrass. A note to mention is that although some types of wheat, like spelt, are better tolerated by people with a wheat intolerance, they all still contain gluten that is toxic to people with coeliac disease.

Daily Science Factlet – buttery wines

Sometimes, there is nothing better in this world than a glass of Californian Chardonnay. Cool but not too cold – you want to make sure it’s warm enough to release the delicious volatiles that make up its ‘bouquet’. And the taste – like buttered toast, sprinkled with vanilla. Now don’t worry, this hasn’t suddenly become a wine tasting blog, we’re getting to the science… Because that butteriness, plus the toasty and vanilla aromas in wines like Californian Chardonnay are courtesy of just a few chemicals.

The buttery aroma/flavour comes from a compound called diacetyl. This is also found in cultured butter, hence the similarity. The process that produces the diacetyl in wine is known as malolactic fermentation. This is a second bacterial fermentation of the wine using Oenococcus* bacteria that break down malic acid from the fruit into lactic acid and aroma compounds like diacetyl.

The toasty vanilla aromas come from the oak barrels the wine is fermented in. Vanillin is present in the wood while it is growing, along with tannins and other aroma compounds like eugenol (which smells of cloves) to stop boring insects munching their way into the wood. The toastiness comes from when the insides of barrels are ‘toasted’ to add flavour to the wines stored in them. The heating breaks down structural molecules in the wood (like cellulose and lignin) into chemicals like acetaldehyde (that smells of green apple), guiacols (that give that toasty, smoky smell) and furans (that smell sweet and bready). When the wine is fermenting in the barrels, it reacts with the wood and absorbs many of these flavour and aroma compounds, giving the characteristic bouquet.

* – Thanks to Tony Milanowski who pointed out that the Leuconostoc bacteria involved in malolactic fermentation had in fact been reclassified as Oenococcus.

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.