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A to Z of Brewing Terms



Alcohol by volume. Given as a percentage. This tells you how much of a drink is alcohol.



Mixing the wort with air so that oxygen is dissolved into it. This is desiable just before pitching because yeast need oxygen. At other times it is damaging to the beer so should be avoided. (See also Hot Side Aeration)



Fermentable ingredients in a beer recipe other than malt. They do not contain enzymes that can change starch into sugars so must be mashed with malts that do. They include sugars of various kinds, wheat, rice and corn.



A device that allows CO2 produced during fermentation to be released from a fermenting vessel whilst stopping air (which may contain bacteria or wild yeasts) from entering.


All grain brewing

Brewing beer from grains rather than from malt extract. (See Mashing)



A beer other than a lager type beer. Performed by top fermenting yeast.


Alpha acids

Chemical compounds found in hops which impart bitterness when dissolved in beer



Alpha acid units. A measure of the amount of bittering compounds (alpha acids) present in a particular hop.



How much of the sugars in fermented drinks are converted to alcohol. Low attenuation means that fermentation stops with a larger amount of sugars still present giving a sweeter and less alcoholic drink. Normally this depends on the type of yeast used for the fermentation.



A alcoholic drink made from fermented malt flavoured and preserved with hops.


Beer Kit

A kit of ingredients where the process of mashing and boiling with hops has been done by the manufacturer making it very easy to make beer. The kit will also include the yeast needed. Some kits need extra ingredients such as sugar or beer enhancer to be added whilst others contain everything needed except the water that must be added.



A hard deposit that sometimes precipitates from beer. A mixture of calcium oxalate and proteins it has a rough surface that provides a surface that bacteria can grow on and is difficult to remove.


Blowoff hose

An alternative to a small airlock consisting of a tube leading from a fermenter into a bucket of water. The CO2 bubbles away through the water but air cannot the other way. Useful for a large fermenter or where a fermentation is very vigorous.


Brewing kettle

A vessel usually heated by electric elements or a gas burner which is used to boil wort.



The process of adding dissolved carbon dioxide to a beer or sparkling wine. This may be done naturally by yeast or artificially using CO2 gas. Most homebrewers and winemakers do this naturally using the process of secondary fermentation.


Cold break

A mix of unwanted substances that precipitates out of a beer when it ios cooled very quickly after boiling. If beer is cooled too slowly this does not happen and the beer may not keep as long and may be hazy. Some kind of wort chiller is needed to cool the beer fast enough.



A period of storage after bottling or putting in casks or pressure vessels. Secondary fermentation happens during this time which makes a big difference to the flavour and mouthfeel of beer. This also applies to sparking wines.



A mashing system where potions of the mash are removed to a boiling vessel and then returned to the mash. This system is characteristic of traditional continental brewing and can make a big difference to the finished beer.



A complex sugar molecule which may be produced during mashing. Dextrins are less fermentable than glucose of smaller sugars and add to the body of a beer.



Another name for glucose. Dextrose monohydrate is sold as Brewing Sugar



A substance that gives a buttery smell and flavour to beer. In darker, more complex beers it may be quite helpful to the flavour but light beers and especially lagers are better without it.


Diacetyl rest

A period of maturing on the yeast after fermentation has finished to give the yeast chance to naturally remove the diacetyl. A slightly higher temperature is usually used during this period.


Dimethyl sulphide (DMS)

A flavour compound in beers that may be benfical in small quantities for lager type beers but causes off flavours that are like boiled cabbage when there is too much.



In brewing, enzymes are substances that usually break down other substances. An example is amylase, an enzyme that breaks down insoluble starch into smaller, soluble sugars.



When yeast change sugars into CO2 and alcohol.



The normal size of cask used by brewers to sell ale to pubs. The volume is 9 gallons.



When yeast clump together. This often causes them to fall to the bottom of the fermenter. If this happens too early the fermentation may stop but is needed for beers and wines to clear properly.



In brewing this refers to ‘Specific gravity’ which gives a measure of the amount of sugar a beer. Measured with a hydrometer, gravity reduces as fermentation proceeds .



Flowers of the hop plant which add bitterness and flavour to beer. There are many varieties of hop with different amounts of bitterness compounds (alpha acids) and very different flavours.


Hot break

In all grain and extract brewing a foam builds up at the start of the boil. This needs to be stirred back into the liquid where it will sink to the bottom and become part of the trub. If a good rolling boil is not reached the substances in this foam will stay in the beer and will not be good for the clarity, taste or keeping qualities of your beer.


Hot side aeration

This is when wort comes into contact with oxygen whilst it is hot. The warmer the wort the worse the effect of oxygen will be on it. The problem is that yeast needs oxygen to reproduce when first pitched. It is essential to get as much oxygen to dissolve into your wort before you pitch your yeast but NOT UNTIL THE TEMPERATURE IS BELOW 30 degrees C!!!!!  This is one reason why yeast is rehydrated in a small batch separate from the main brew. A little oxygen damage will occur but the amount is small enough to be ignored.



An instrument used to measure the specific gravity of beer or wine before, during and after fermentation.



International Bittering Unit.  A measure of the amount of hop bitterness actually present in a beer. (see also AAUs)



The foamy head containing lots of yeast that builds up on top of a brew during fermentation.


Lag time

The period immediately after pitching when yeast adapt to their new environment and reproduce to much greater numbers before starting fermentation. You may not see anything happening but it is!



A continental style of bottom fermented beer which requires long storage for maturation before being ready to drink. (beers sold in the UK under this name do not always undergo such a maturation period)



The flushing out of soluble sugars from grain that has been mashed. (See also Sparging)



In German, to lager means to store and refers to the conditioning period where a beer is left for off flavours to be dealt with by the yeast.


Lambic beers

Originally from Belgium, these beers are fermented by bacteria rather than yeast and have a distinctive acidic flavour. An acquired taste.



What brewers call the water they brew with.


Maillard reactions

Chemical reactions which cause a beer to become darker in colour. More noticeable the longer a beer or malt extract is left and made worse when heat is used.



A partially germinated grain that has begun to change stored starch to soluble sugars. Malt is used to make beer.


Malt extract

A concentrated form of the sugars released from malt. It may be sold in the form a thick liquid or a dry powder. Brewers can use this rather than perform the hard work of mashing etc. Beer kits contain malt extract usually with hop bitterness already added.



To mix malt with water and keep it at a specific temperature so that enzymes in the grain can convert more starch to soluble sugars and so form a wort for fermenting into beer.


Mash tun

The vessel used for performing the mashing process. There are many forms of mash tun.



A very small commercial brewery. The exact size is a matter of opinion but is normally thought to be one producing 3 barrels of beer (108 gallons) in one batch.


Original gravity

The hydrometer reading of the wort before it is fermented. You can use this to predict the likely finished strength of your beer.



A scientific measure of the acidity or alkalinity of a liquid. The range is from very acid pH1 through neutral (pH7) to very alkaline (pH14). Beers are usually around pH 4.5 – 6.2. Wines are usually around pH2.8 - 4.4



Adding yeast to start a fermentation



Adding fermentables to bottles or pressure barrels to be converted into CO2 to condition the beer. These may be malt or sugar since the amount used is very low. Normal priming levels are ½ teaspoon per 500ml bottle for ales to a full teaspoon per 500ml bottle for lagers. The more sugar the more CO2. Too much can cause bottles to explode whilst too little causes flat and boring beer.



The transfer of beer or wine to another container, usually using a siphon. Sediment from the bottom of the fermenter is left behind so that a clearer liquid results.


Rehydration (of yeast)

When dried yeast is sprinkled directly onto wort the yeast undergo a shock due to not being able to adapt quickly enough to their new environment. Since a dried yeast pack contains billions of cells you can afford for many of them to be killed but rehydrating the yeast before pitching helps more to survive. This is how to do it:

Sanitise a cup 2/3 fill it with boiling water from a kettle. Cover it with foil and let it cool until it is around 35 degrees C.  Now sprinkle the yeast on top and don’t stir it yet. Cover again and leave it for 15 minutes.  Now stir with a sanitised spoon, leave for another 15 mins and then pitch into your wort. The higher temperature will allow the yeast to adapt more easily and there will be many more live yeast cells to get going on your wort. If you are asking why not just pitch the yeast into wort that has only been cooled to 35 degrees C then read the section on Hot Side Aeration.



The process of killing most of the microorganisms in something so that added yeast has a chance grow and ferment. This is often called sterilisation but strictly speaking that involves a harsher process that kills all bacteria etc. This is necessary in an operating theatre but not in brewing.



If yeast is purchased in liquid for the pack will contain far fewer yeast cells than a decent pack of dried yeast. In these circumstances it may be necessary to build up the numbers by starting the yeast off in a small volume of dissolved malt. Dried yeasts are now available in much greater variety than a few years ago and contain many more yeast cells to begin with. Dried yeasts are intended by the manufacturer to be sprinkled directly onto the wort and a starter is not needed. Rehydration may be a good idea however.



Killing microorganisms in a lliquid or on equipment.


Secondary fermentation

The fermentation that occurs in bottles, pressure barrels or casks that carbonate a beer.



Sprinkling the mashed grains with hot water as part of the lautering process.


Stuck fermentation

When a yeast stops fermenting before it has reached the intended level of alcohol. You can diagnose this by taking a reading with a hydrometer.



Normal sugar. Not recommended for use in beers unless the intended strength is high and plenty of malt is already present. Otherwise using sugar in beer produces bad flavours and is a common cause of stuck fermentations.



A group of chemical compounds found particularly in red wine, cider and to some extent beers. They have an astringent, almost woody flavour that is needed in some drinks but should not be too strong. The outer husk of malt grains contain lots of tannins and this is why mashed grains should not be squeezed



The sediment found at the bottom of a fermenter or brewing kettle


Wheat beer

A style of beer that uses a significant proportion of malt derived from wheat rather than barley. Often deliberately intended to be cloudy.



The amber liquid containing sugars and flavours from grain that has been mashed. This is then boiled with hops, cooled and fermented to make beer.


Wort chiller

A device for quickly cooling wort that has been boiled with hops to the temperature where yeast can be added (pitched).



A single celled fungus that has the ability to live with or without oxygen. When first added to wort or wine must the yeast use dissolved oxygen to live and reproduce and later live without oxygen whilst getting their energy from sugars of various kinds and excreting alcohol and CO2 as waste materials.

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