Fermentation
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50 free Fermentation trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Fermentation is one of the oldest tricks in biology and one of the oldest in the kitchen. Microbes use it to live without oxygen, and people have borrowed it for thousands of years to raise bread, brew drinks, preserve vegetables and, more recently, to manufacture medicines. This quiz covers both sides. Some questions deal with the science: what goes in, what comes out, where the energy comes from and who worked it all out. Others travel the world's fermented foods, from breakfast tables in Japan to a famously smelly tin of fish in northern Europe, and a few visit the animals that ferment for a living. The early questions suit anyone who likes food and general knowledge, and the later ones match what is taught in GCSE, high-school and first-year university biology. Every answer comes with a short explanation, so a wrong guess still teaches something.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which popular pet fish can survive long spells without any oxygen by making alcohol in its muscles?
Goldfish
Goldfish and their wild cousins, crucian carp, turn the waste from oxygen-free living into alcohol that drifts out through the gills. Most backboned animals die within minutes without oxygen.
Q 02Captain James Cook took sauerkraut on his long sea voyages to protect his crew from which disease?
Scurvy
Scurvy comes from a lack of vitamin C, which raw sauerkraut supplies. Fermenting the cabbage also gave it the long shelf life needed for voyages that lasted years.
Q 03Surströmming, a fermented herring notorious for its smell, is a traditional delicacy of which country?
Sweden
Sweden's sour herring keeps fermenting inside the tin until the can bulges. The smell is so strong that it is usually opened and eaten outdoors.
Q 04Iceland's national dish hákarl is made by fermenting and then drying the meat of which animal?
Shark
Shark meat from the Greenland species is poisonous when fresh because it is full of urea. Curing and hanging it for months makes it safe, though the ammonia smell makes many first-timers gag.
Q 05Which sweet treat gets its flavour from seeds fermented in their own pulp for days before roasting?
Chocolate
Chocolate begins as cacao seeds heaped under mats or banana leaves for three to seven days. The heat of fermentation turns the purplish beans brown and starts building the flavour.
Q 06What is the name of the rare condition in which microbes in the gut ferment food into alcohol?
Auto-brewery syndrome
Auto-brewery syndrome can leave people slurring and unsteady without a single drink. It has even been raised in court as a defence against drink-driving charges.
Q 07Deep-tank fermentation let drug makers brew enough of which antibiotic to supply Allied troops on D-Day?
Penicillin
Penicillin was once so scarce that it was recovered from patients' urine and reused. Fermentation tanks changed that, and 2.3 million doses were ready for the Normandy landings.
Q 08Which hormone, grown in tanks of engineered bacteria, became the first licensed genetically engineered drug?
Insulin
Insulin from engineered E. coli went on sale as Humulin in 1982. Until then, people with diabetes relied on hormone extracted from the pancreases of cows and pigs.
Q 09Chaim Weizmann, whose fermentation process made acetone for explosives, became which country's first president?
Israel
Israel's first president was a biochemist whose process kept Britain supplied with cordite propellant in World War I. He is considered the father of industrial fermentation.
Q 10Which small fish goes into Worcestershire sauce, the fermented condiment invented by two English pharmacists?
Anchovies
Anchovies appear on a 19th-century Lea & Perrins ingredient list that turned up in a skip at the factory in 2009. The exact recipe is still a trade secret.
Q 11Which gas, released by yeast as it ferments sugar in dough, makes a loaf of bread rise?
Carbon dioxide
Carbon dioxide forms bubbles that stretch the dough into a foam. The yeast makes alcohol too, but less than 2% of it is left after baking.
Q 12Which French chemist showed in the 1850s that living microbes, not mere chemistry, cause fermentation?
Louis Pasteur
Louis Pasteur went on to sum up fermentation as life without air. He also traced the yeast that ferments wine to the skins of the grapes themselves.
Q 13Which acid, made by bacteria fermenting sugars, gives yogurt and sauerkraut their sour tang?
Lactic
Lactic acid does double duty: it sets the milk protein that thickens yogurt, and it preserves sauerkraut for months without a fridge.
Q 21Which tangy bread is raised by a starter of wild yeast and bacteria rather than packaged baker's yeast?
Sourdough
Sourdough travelled with Klondike gold miners, who carried pouches of starter on their belts and guarded them from the cold. In fact freezing does not kill a starter, but excessive heat does.
Q 22Most yeast stop fermenting at about 15% alcohol, so stronger drinks such as whisky need which extra process?
Distillation
Distillation concentrates the alcohol from a liquid that has already been fermented. Spirits typically leave the still above 50% and are diluted before bottling.
Q 23Which fruit is too bitter to eat straight from the tree and is usually cured and fermented first?
Olives
Q 14Which type of alcohol, the one found in beer and wine, does yeast make when it ferments sugar?
Ethanol
Ethanol is really the yeast's waste product, and each glucose molecule yields two molecules of it. The same reaction now fills fuel tanks as well as wine glasses.
Q 15Yeast, a one-celled organism behind bread and beer, belongs to which kingdom of living things?
Fungi
Fungi include yeast alongside moulds and mushrooms. Most yeasts multiply by budding, in which a small daughter cell swells out of its parent.
Q 16Fermentation earns a cell just two molecules of which energy carrier per glucose, far fewer than respiration?
ATP
ATP is the cell's energy currency. Respiration with oxygen can wring roughly 30 molecules from the same glucose, about fifteen times as many.
Q 17Mead, possibly the most ancient alcoholic drink of all, is made by fermenting which ingredient with water?
Honey
Honey supplies the sugar in mead, which may have been discovered 20,000 to 40,000 years ago, before farming or pottery existed.
Q 18Which Korean staple is made in bulk and left to ferment before each winter, a custom on UNESCO's heritage list?
Kimchi
Kimchi season is called gimjang, a month when households prepare enough to last the whole winter. UNESCO added the custom to its heritage list in 2013.
Q 19Which fizzy drink is made by fermenting sweetened tea with a rubbery mat of bacteria and yeast?
Kombucha
Kombucha's floating mat is known as a SCOBY, a mother or a mushroom, though it is really a film of microbes. In Chinese it was once called sea treasure because it looks like a jellyfish.
Q 20Which kitchen staple, made by letting bacteria work on alcohol, takes its name from Old French for sour wine?
Vinegar
Vinegar forms in a double fermentation: yeast first turns sugar into alcohol, then bacteria turn that alcohol into acid. A slimy raft of those bacteria is known as the mother.
Olives owe their raw bitterness to a compound called oleuropein, which curing and fermenting strip out. About 80% of the harvest never reaches the table and is pressed for oil.
Q 24Which dark British spread is made from the yeast left over after beer has been brewed?
Marmite
Marmite got its first factory in 1902 in Burton upon Trent, where the Bass brewery supplied the spent yeast. A German chemist had shown that brewer's yeast could be concentrated, bottled and eaten.
Q 25Caribbean rum traditionally begins when yeast ferments which by-product left over from refining cane sugar?
Molasses
Molasses was a mere leftover until, by the traditional account, enslaved workers on 17th-century Caribbean plantations found that it could be fermented into alcohol.
Q 26Perry is an alcoholic drink made much like cider, but by fermenting the juice of which fruit?
Pears
Pears grown for perry are small and bitter, much as cider apples differ from the ones sold for eating. The drink is a speciality of England's western counties and of Normandy.
Q 27Which country fuels much of its car fleet with alcohol fermented from its vast sugarcane crop?
Brazil
Brazil no longer has any light vehicles running on pure petrol: every litre sold is blended with cane alcohol, and flex-fuel cars can run on any mix of the two.
Q 28Cattle belch which greenhouse gas, made as microbes ferment grass inside their stomachs?
Methane
Methane from cattle, sheep and their relatives makes up around a third of the methane released by human activity. About 95% of it leaves as burps, not from the other end.
Q 29What do bakers call the final rest in which yeast ferments shaped dough and puffs it up before baking?
Proofing
Proofing is called proving in Britain and Australia. Bakers use the same word for soaking dried yeast in warm water to wake it up before mixing.
Q 30Kumis, a mildly alcoholic drink of the Central Asian steppe, is made by fermenting the milk of which animal?
Horse
Horse milk carries more sugar than the milk of cows or goats, which is why kumis ferments into something mildly alcoholic as well as sour.