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Production of Ethanol by Fermentation: Mead


The brewing of alcoholic beverages is quite ancient. The first written records to survive into modern times already record a vigorous commerce in beer. The Babyonian government (c 1800 BC) enforced standards for beer and in that time period the brewing of beer was almost exclusively a woman's occupation.

Beer is brewed from grains such as wheat, rice, and barley. First the grain is malted. This involves soaking the grain in water and allowing it to sprout. The sprouting process produces enzymes which will be used to convert the starches in the grain into fermentable sugars. After a few days, the sprouts are heated (thus killing them) and dried, either in an oven or by setting them out in the sun. At the end of this process what you have ar shriveled up little sprouts, loaded with enzymes (called diastase) and with much of their starch converted to sugars.

Next the malt is added to more grain and water in a process called mashing. In the mash, the diastase enzyme from the malt converts the starches in the non-malt grain into fermentable sugars, mostly maltose. The temperature must be carefully controlled for the enzymes to work most efficiently. The mashing process takes a couple of hours, at the end of which the solids are filtered out, leaving a solution rich in sugars called the wort. The wort is cooled and diluted with water to achieve the desired concentration of sugars. The cool wort is now ready for fermentation.

All of this work been simply to produce a solution of sugars in water. Any sugar can be fermented to produce ethanol. If the sugar is already present, we can skip the malting and mashing steps. Wine is made from fruit juice, usually grapes or apples. The fruit is pressed to release its juice, which is rich in the sugar fructose. Cane sugar, sucrose, can also be fermented. But suppose you are the first guy wandering around in the woods. Where are you going to get sugar? Honey! Yes, the bees have been hard at work, saving you the trouble of malting and mashing! The beverage produced by fermenting honey is called mead.

Mead is a much more primitive beverage than beer or wine. Of all the alcoholic beverages, it requires the least preparation prior to fermentation. That is not to say that it is easy to produce a good-tasting mead. In fact it is terribly easy to produce bad-tasting mead. So even though mead is the simplest alcoholic beverage, it will still be a challenge for you. The principle challenges are to control the concentration of sugar in the must (akin to the wort for beer) and to ensure that only the desired yeast (not bacteria) thrive in the fermentation vessel.

Biology and Chemistry of Fermentation

The most important requirement for fermentation of alcohol is the presence of single-celled organisms called yeast. Your first priority is to make sure that yeast and only yeast is present in your must. Cleanliness is the key to success in this requirement. Bacteria also thrive in sugar-rich solutions and they produce acidic rather than alcoholic wastes. Wash everything thoroughly to avoid bacterial contamination.

Yeasts will undergo a three-part life cycle during the course of fermentation. In the initial, aerobic phase, they have oxygen available to them and completely respire any sugars present to carbon dioxide and water:
C6H12O6(aq) + 6 O2(g) ---> 6 CO2(g) + 6 H2O(l)
Aerobic conditions are what yeasts like best and if left to their own devices they will happily convert all available sugars to carbon dioxide and water, not alcohol.

Most organisms will die without access to oxygen. Yeasts prefer the presence of oxygen but they have the ability to live without it. In this phase, the anaerobic phase, they are only able to partially digest sugars:
C6H12O6(aq) ---> 2 CO2(g) + 2 C2H5OH(aq)
No oxygen is neccessary during this phase. In fact, if oxygen is present, the yeasts will switch to aerobic respiration. The compound C2H5OH is one member of the alcohol family, ethanol. In order to produce it, we must have a sugar solution, protected from both oxygen and bacteria, supporting an active yeast culture. Eventually, one of two things will happen. Either the yeast will consume all available sugar or the alcohol concentration will become so great that the yeast can no longer thrive. If there is too much honey, there will be sugar left over when the yeasts die of alcohol poisoning and you will get a sweet mead, which is not a disaster, but if your goal is to produce alcohol you will not have the maximum yield of alcohol for the sugar you put in. If there is not enough honey, the yeasts will starve before the alcohol level is at the toxic level (toxic for yeasts, that is) and you will get wimpy mead. Again, no catastrophe but not maximizing your yield of alcohol. If the amount of honey is just right the poor yeasts starve just as the mead is becoming alcoholic enough to kill them anyway. Such a mead will have an alcohol content of 10-12% and have very little sugar leftover. The yeasts enter a dormant phase and settle to the bottom of the container, completing their life cycle.

A crucial aspect aspect of home brewing is assuring that only the intended yeasts thrive during the fermentation process. Once made, the ethanol is susceptible to bacterial contamination. Bacteria are able to digest ethanol, but they require oxygen to do so:
C2H5OH(aq) + O2(g) ---> CH3COOH(aq) + H2O(l)
This is why wine "goes sour" after it is opened. Acids have a sour taste. If this is done intentionally, the result is vinegar, which is typically 5% acetic acid in water. If bacteria are allowed to contaminate the must, they will compete with the yeast for sugar and alcohol. Your first line of defense is to sterilize everything which will come in contact with the fermenting must. Wash everything with soap in order to kill any bacteria and wild yeasts that may be present. We must also ensure that no bacteria or wild yeasts can contaminate the must once fermentation has started. Your second line of defense is to protect the must from oxygen. We could just seal the container, but the yeast produces carbon dioxide gas as well as ethanol and a sealed bottle would eventually explode from the pressure. Serious homebrewers use a fermentation lock to allow gas to escape while preventing contamination. We will simply use a loose-fitting cap to allow gas to escape. In additon, once the fermentation is proceeding, you may cover this loose cap with a clean, dry, cloth to prevent contamination by airborne microbes.

The Law

Please remember that it is illegal for anyone under the age of 21 to consume alcoholic beverages. I have been in contact with Mr. Ron Reynolds of the Bureau of Alcohol, Tobacco, and Firearms in Philadelphia. It is his opinion that it is OK for everyone in the class to participate in this project but that it is still illegal for those under 21 to drink the product. Bummer about the drinking part but be thankful that you are allowed to participate in the project. Anyway, mead gets better with age (a year or more is best). Imagine how good it will be by the time you are old enough to drink it!

Since February 1979 it has been legal for adults over 21 to brew not more than one hundred gallons of beer each year ( thanks Jimmy Carter!) for their own personal use. It is still illegal to sell homebrew or to serve it to minors. It is also illegal to distill alcohol for beverage purposes. See the alcohol project for more information.

Other Mead Pages

Books on Reserve

The Mead Quiz

The mead quiz consists of three question on any of the following topics.


To make mead in a 2 L plastic soft drink bottle you will need:

  1. a 2 liter plastic bottle with cap, both scrupulously clean
  2. clean water
  3. 12-16 ounces of honey (Do not take honey from the commons!)
  4. about 5 mL of rehydrated yeast
  5. one tablet of dried yeast extract


  1. Scrupulously clean everything with soap and water.
  2. Pour honey into your bottle and add hot water untill the bottle is full to the shoulder.
  3. Place cap on bottle and allow to cool to room temperature.
  4. Estimate the potential alcohol content in your mead: percent alcohol = ounces honey / liters mead (approximately). 16 ounces of honey in 1.75 liters of mead has a potential alcohol content of about 9%.
  5. Bring your bottle to me. I will measure the sugar content using a hydrometer, add a yeast nutrient tablet, and pitch the yeast.
  6. Once you get your innoculated bottle home, unscrew the cap and then screw it loosely onto the bottle. Remember, you want to allow carbon dioxide to escape while preventing oxygen and bacteria from contaminating your mead.
  7. Place bottle in a container to catch any overflowing foam.
  8. Within 24 hours you should see foam in the bottle. This foam may "blow off" past the cap and into the container in which the bottle sits. This foam can be discarded.
  9. At all times the cap must be loose enough to allow gas to escape but not so loose that the cap is blown off.
  10. Allow fermentation to proceed for 3-4 weeks. Yes, weeks! Be thankful, if you leave out the yeast extract it can take months!

You can get fancy by adding additional flavors and conditioners. You can also improve the clarity of the mead by racking, that is, siphoning off the dead yeast bodies which settle to the bottom. See the other mead pages and books for advanced mead tips.

Criteria for Success

You can start your mead whenever you wish. But you should have passed the mead quiz before you bring it in for evaluation. You should plan on at least 4 weeks of fermentation.

I will evaluate your mead for quality and alcohol content. First I will smell your mead. If it makes me gag (usually because of bacterial contamination), you fail. I will then taste your mead. If it makes me gag (usually because of bacterial contamination), you fail. Finally, I will measure the alcohol content using a hydrometer. If it is less than 5% alcohol, you fail.

The whole evaluation process should take no more than 5 minutes. If you fail any part, you fail the entire project. You may, however, try again until you pass.