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Bionic Leaf Turns Sunlight Into Liquid Fuel 10 Times Faster Than Nature
By Tim Radford
Scientists in the U.S. claim to have beaten nature at its own game. They have created a “bionic leaf" that exploits sunlight to create biomass—and they say their invention is now 10 times more effective than an oak or maple leaf.
Two separate laboratories at Harvard University have co-operated to devise, enhance and test a system that uses sunlight to split water molecules and feed the hydrogen to bacteria that then produce liquid fuels. The next task is to scale up the experiment to produce carbon neutral fuels to combat climate change.
“This is a true artificial photosynthesis system," Daniel Nocera, a leading researcher in renewable energy who is professor of energy at Harvard said. “Before, people were using photosynthesis for water-splitting, but this is a true A-to-Z system and we've gone well over the efficiency of photosynthesis in nature."
Photosynthesis was perfected by the plant world more than 3 billion years of evolution. It drives the entire living world and it is the primary source of all fossil fuels.
Climate change became a problem only when humans started to extract ancient sunshine in the form of coal, oil and natural gas, stored in the Carboniferous rocks and put it back in the atmosphere.
Just as wood fires from felled timber make no difference to the atmosphere's carbon dioxide levels—because the same forest that shelters the fallen tree will absorb it again—so biofuels converted from surplus maize or sugarcane should, in theory, make no difference to global warming.
So the idea of what the Harvard team call “bionic leaf 2.0" is an attractive one. It could deliver liquid fuels in convenient form that would make no difference to the planet's overall carbon budget. In effect, it could bypass the vegetation stage.
Chemists and engineers the world over are racing to exploit human ingenuity and deliver brilliant solutions, including artificial leaves that can capture carbon dioxide. The challenge is to do so effectively, cheaply and on a massive scale.
Which is why Prof. Nocera's lab teamed up with microbiologists led by biochemist and systems biologist Pamela Silver, of Harvard Medical School.
The scientists report in Science journal that they have devised a hybrid system based on cobalt-phosphorus alloy catalyst partnered with bacteria called Ralstonia eutropha, which splits water into oxygen and hydrogen at low voltages.
The microbes consume the free hydrogen and, in the presence of oxygen and carbon dioxide, begin some organic chemistry. So far, the system has made isobutanol and isopentanol and even a bio-plastic precursor product.
The Harvard scientists say their bionic leaf converts solar energy to biomass with an efficiency of 10 percent. The fastest-growing plants do the same with an efficiency of 1 percent.
What works in a laboratory may be tricky to translate into large-scale production, but the researchers are confident they have something that works.
Prof. Nocera said: “It's an important discovery. It says we can do better than photosynthesis. But I also want to bring this technology to the developing world as well.
“If you think about it, photosynthesis is amazing. It takes sunlight, water and air—and then look at a tree. That's exactly what we did, but we can do it significantly better, because we turn all that energy into a fuel."
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Bread has been a source of basic nutrition for centuries, the holy trinity being wheat, maize and rice. It has also been the reason for a lot of innovation in science and technology, from millstones to microbiological investigations into a family of single-cell fungi called Saccharomyces.
Chemical leavening<p>If you like a little heft in your loaf, you will need a leavening agent.</p><p>For those short on time, you can use baking soda. That's a chemical compound of sodium bicarbonate mixed with potassium bitartrate, or cream of tartar.</p><p>Soda breads have their traditions in parts of eastern and central Europe, and in Ireland and Scotland, with Melrose loaves and "farls."</p><p>They can taste a bit bland, though, and are often considered only as an emergency solution on Sundays. No disrespect intended: They taste just fine fresh from the oven.</p><p>Whether it's chemical or more "natural," leavening relies largely on the production of carbon dioxide.</p><p>When you mix an acid, such as vinegar, buttermilk, yogurt or apple cider, with an alkaline compound like baking soda, you get CO2. That CO2 creates bubbles, which in turn capture steam in the oven and allow a bread to rise.</p><p><span></span>But it's better with yeast. Tastes better, too. It just takes more time. </p>
What is yeast?<p>There are yeasts all around us — on grains, in the air, in biofuels. It even lives inside us, but that's not always a good thing.</p><p><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1090575/pdf/1471-2334-5-22.pdf" target="_blank">Candida yeast</a> can cause infections of the skin, feet, mouth, penis or vagina if it builds up too much in the body.</p><p>One of the most common yeasts, however, is <em>Saccharomyces cerevisiae</em>. That's <a href="https://www.dw.com/en/an-early-beer-archaeologists-tap-ground-at-worlds-oldest-brewery/a-45480731" target="_blank">"brewer's"</a> or "baker's" yeast.</p><p>You can get fresh baker's yeast, often in 42-gram (1.48-ounce) cubes, or as dried yeast (quick action or active, which requires rehydration) in a sachet of 7 grams.</p><p>There's little difference: One is compressed and the other is dehydrated and granulated. But they do the same thing, essentially. </p><p>Some commercial yeast producers add molasses and other nutrients. But natural yeast has plenty of useful nutrients in it anyway, including B group vitamins, so who knows whether it's good or necessary to add them. </p>
How does yeast work?<p>When you mix flour, yeast and water, you set off a veritable chain reaction. Enzymes in the wheat convert starch into sugar. And the yeast creates enzymes of its own to convert those sugars into a form it can absorb.</p><p>The yeast "feeds" on the sugars to create carbon dioxide and alcohol. The yeast burps and farts, releasing gases into the mix, and that creates bubbles to trap CO2. </p><p>It's a vital fermentation process that breaks down the gluten in the flour and helps make your bread more digestible.</p><p>The yeast cells split and reproduce, generating lactic and carbonic acid, raising the temperature and ultimately adding flavor to the mix.</p><p>The longer you leave the yeast to do its thing, the better for your bread. Time is more important than the amount of yeast. </p><p>In fact, that's an enduring question — how much yeast? I'll use 20 grams fresh yeast for 500 grams of flour. Others say that's enough yeast for 1 kilo. If you are converting a dry-yeast recipe to fresh yeast, some bakers advise tripling the weight. So, if a sachet of dried yeast is 7 grams, your fresh yeast is 21 grams.</p><p><span></span>But that also depends on the flours you are using, temperatures in the bowl and the room, and a host of other things. You'll just have to experiment and see. No number of books (and I've read a stack on bread) will help as much as trial and error.</p>
Wild yeast: Sourdough<p>So, good bread needs time. If you have a lot of time, why not move it up a notch and grow wild yeast — a sourdough starter — in your own home?</p><p>A sourdough starter is not to be mistaken (as it often is) for the leaven, or "mother," "sponge," or <em>levain</em>. That's more a second stage, a descendant of the starter. You take a scoop from your starter and add it to another flour and water mixture when you prepare the dough for a new loaf. </p><p>The sourdough process utilizes yeasts naturally present in flour and … yet more time. A longer fermentation process allows a richer lactic acid bacteria <em>lactobacilli</em> or LAB to evolve, and that can be healthy for your gut microbiome.</p><p>It's simple enough to start a sourdough starter. All you need is flour, warm water and time.</p><p>Some suggest equal measures of whole-grain flour and water at 28 degrees Celsius (82 degrees Fahrenheit), some say room temperature — just don't let the water exceed 40 C or the yeasts will die. Some suggest two parts flour to three parts water. But it's up to you whether you want a drier or wetter starter. You will know only through experimentation. </p><p>Some say you should filter tap water to remove chemicals like fluoride and avoid using water that's boiled and then cooled. Others say that really doesn't matter.</p><p>The main thing is, keep it clean and give it time. Days, weeks, months and years.</p>
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