Hops

Hops are the ingredient that give a beer its distinctive flavouring. Hops are used for both their bittering qualities and their aroma qualities. There are many varieties of hops available to the home brewer but it is important to know which hops do what. They can be broken down into three categories - Aroma Hops add flavour to the beer through the natural oils contain in the hops. Aroma hops are usually added in the last few moments of the boiling process.

Bittering Hops are primarily used for the bitterness imparted from the hops. These hops are usually added quite early into the boil as it takes the vigourous boil to separate the alpha acids contained in the hops that create the bitter flavour. Dual Purpose Hops can be used for both their bittering qualities and their aromas depending when the hops are added to the boil.

Alpha Acids

Hops contain both Alpha Acids and Beta Acids, the most important one to the home brewer being the alpha acids. Alpha acid is the bittering agent in the hop. Different types of hop contain different quantities of alpha acid - the percentage is usually stated on the packet - but there are many factors contributing to the level of alpha acid contained in any one variety of hop so any indication should only be used as a rough guide.

Below is a chart containing various hop varieties with an indication of the alpha acids present. Note though that the percentages of alpha acids can vary from harvest to harvest.

Hop Alpha Acid Chart

Hop Type	Alpha Acid	Location	Type
Admiral	14.6%	UK	Bittering
Amarillo	5%	USA	Aroma
Bodecia	7.9%	UK	Dual
Bramling Cross	6.3%	UK	Aroma
Brewers Gold	6.1%	Germany	Aroma
Bullion	6.5-9%		Bittering
Cascade	5-7%	USA	Aroma
Centennial	7.5-11%	USA	Aroma
Challenger	7.6%	UK	Dual
Chinook	14%	USA	Bittering
First Gold	8.3%	UK	Dual
Fuggle	4.9%	UK	Aroma
Golding	5.7%	UK	Aroma
Herald	12.7%	UK	Bittering
Hersbrucker	2.9%	Germany	Aroma
Liberty	4.5%	USA	Aroma
Mount Hood	4.4%	USA	Aroma
Northdown	8.4%	UK	Dual
Northern Brewer	8.2%	Germany	Dual
Phoenix	11%	UK	Bittering
Pilgrim	11.6%	UK	Bittering
Progress	6.4%	UK	Aroma
Saaz	3.4%%	Czech	Aroma
Sovereign	5.7%	UK	Aroma
Styrian Golding	4.5%	Slovenia	Aroma
Target	11.4%	UK	Bittering
Whitbread Golding	6.4%	UK	Aroma

Beta Acids

Beta Acids are not normally calculated as their impact on the flavourings of beer is negligible unless your hops are old. Even then they will only tend to impart a slight bitterness.

Hop Swap

Sometimes when following a recipe you may not be able to obtain a specific hop variety that is required. As we have seen above different hop varieties impart different quantities of alpha acids. A simple way of working out the different quantities required is:

(Amount of Hops Specified (grams) x Alpha Acid of Specified Hops (grams)) ÷ Alpha Acid of Replacement Hops

Essential Oils

Essential oils are released from the hop at temperature however prolonged boiling will diminish the effect the oils will have on your finished brew. These oils are what specifically adds aroma to your beer. To utilise these oils it is usual for the brewer to add the aroma hops into the boil in the last few minutes. As these hops will not be vigorously boiled the oils will not be cooked out and the alpha acids will not add any bitterness to the brew.

Hop Methods

Primary Hops

Primary hops are the hops added to the boiler at the beginning of the boil. They are the hops that have been chosen to add bitterness to the beer.

Late Hopping

Hops that impart aroma are usually 'late hopped' as little as a couple of minutes towards the end of the boil giving the hops just enough time to impart their aroma.

Post Boil Hopping

This is basically a process of steeping aroma hops in the wort after the boil has finished and the temperature has dropped reasonably.

Dry Hopping

Dry Hopping is the process of adding a few hop cones to the cask and letting the flavours impart. Care should be taken when using this method as a grassy taste can be emitted from the unboiled hops.

Hop Tea

This is basically the procedure of making a tea out of hops by infusing the hops in a pan of hot water and letting brew for about 30 minutes. Hop 'tea bags' are now commonly available from your home brew store.

Bitterness

The bitterness of the hops in Europe is calculated by in European Bitterness Units (EBC) or International Bitterness Units (IBU). This standard gived the brewer a good guide to bitterness when formulating recipes. In many cases EBUs or IBUs are indicated on the hop packaging.

Hop Utilisation

As matters relating to hops seem to be becoming clearer we hit upon the topic of hop utilisation. This basically relates to the efficiency of alpha acid extraction related to the conditions of brewing. In many circumstances only 25-40% of alpha acid is transferred to the finished brew. Hop utilisation is used to calculate as near as possible this extraction.

Factors effecting utilisation include the type of hop used - usually slower conversion with whole hops, slightly faster with pellets and even faster with hop extracts. The boil time has an effect - it is seen that the longer the boil the more alpha acids will be isomerised although if the boil is too long the extracted alpha acids can diminish. Hop rate can also have an effect on the amount of alpha acids extracted and some brewers add their bittering hops gradually instead of all at once.