Hops add bitterness, flavour, and aroma to beer (as well as giving the finished beer stability and heading ability). The bitterness is an important balance to the malt sweetness. How hops contribute these characteristics of bitterness, flavour, and aroma to beer depends largely on how or when they are added to the brew.

The type of hop is crucial to matching a style of beer. It may be tempting to use a high alpha hop because it provides cheap bittering power, but the resulting flavour may be quite off the intended target. In general if you wish to brew a British ale, use British hops, German lager calls for German hops, etc.

Using Hops For Bitterness

For bittering the hops need to boil for at least an hour (and this should be a good boil not a simmer). This boil causes the alpha acids to be extracted from the hop tissues, and then to be isomerized into a soluble form which means they will stay in your finished beer. If you have boiled your hops for 45 to 60 minutes you will extracted most of their bittering power, and really consider 30 minutes the minimum amount of boiling time for bittering.

Bittering is a matter of degree, and every beer style has its own range of desired bitterness. Recipes will usually indicate the target bitterness with reference to BU (home brew units) which is also expressed as AAU (Alpha Acid Units). These (HBU and AAU) work on the same idea. Take the alpha acid number of the hop you plan on using, and multiply by the ounces of hop. If a 23 litre recipe calls for 10 HBU of Fuggle and your Fuggles have 4.0% AA, then you know you will have to use 2.5 ounces of hops (2.5 X 4.0 = 10). Some popular book use this type of reference. A more accurate system of relating bitterness levels (and one becoming very popular) is the IBU (International Bitterness Unit). This system indicates the actual amount of isomerized alpha acids which are in the beer providing bitterness (units are mg/l) You could use the on-line Hop Bitterness Calculator, or any good brewing software. Fancy programs will take into account the gravity of the wort boil which affects the rate at which alpha acids are isomerized for bitterness, e.g., the higher the gravity of your boil, the lower the rate of isomerization of alpha acids.

There are many factors which affect the actual bittering attained. I have mentioned both wort gravity and boiling time above. These are two very important factors, but one which may be missed is the use of a hop bag. These bags may make it easy to separate the hops from the wort after the boil, but they do reduce bittering potential by about 10% (so if you use these bags, you’ll have to take that into account and adjust the hopping rate).

Remember as well that if you employ a “blow-off” hose to remove the sludge from the top of the krauesen, you may lose another 15% of the bitterness which you calculated.

Lastly, Garetz also suggests yeasts affect bitterness too. Highly flocculent yeasts such as Wyeast 1007, 1278, 1728, 1968 and others, may increase apparent bitterness by 5%. Low flocculent yeast such as Wyeast 1388, 2042, 2247 and others may decrease apparent bitterness by 5%.

Using Hops For Flavour and Aroma
Flavour and aroma profiles are largely determined by the oil content of the hops. These oils tend to be volatile which means they are driven off by boiling and even fermentation. Some of the oils will be bonded with the wort during the boil, so it is important to use the hops you want for a style even during the boil. But many traditional brewing theories incorrectly claim that no flavour profile remains after a boil. So what is the best way to capture hop flavours and aroma?

It appears, and you should experiment here too, that the best way to catch these oils in your beer is through First Wort Hopping (FWH). This is actually an old German brewing method in which hops are added to the wort as it runs from the lauter tun. The resulting bitterness appears to be softer and more pleasing than the bitterness derived from later additions, even though the actually bitterness level is about 10% higher than a start of boil addition. See a summary of FWH results and data at brewery.org.

Here at Paddock Wood, we have been experimenting with Mash Hopping. The hops are added to the mash, rather than to the wort as in FWH. Based on the research of De Clerck and Fix, the theory is that the aromatic oils react in a special way with wort at a higher pH than occurs with wort during the boil (the pH falls during a boil, and reduces the utilization of the hop oils) and at a lower temperature (150F). The complex reaction between hops and the wort results in the formation of more permanent flavour and aroma chemicals remaining in the beer than is the case with traditional hopping methods such as late additions to the brew kettle. It may be important to use pelletized hops in this situation, however, as the release of aromatic oils from whole hop cones is greatly assisted by the action of the boiling wort. The pelletized hops are not transferred to the kettle but remain behind as the mash bed acts as a filter. The hop usage appears to be about 90% less than what you could expect from a start-of-boil addition, but we have not performed any technical data gathering or analysis.
Late hopping means adding the hops for the last 15 minutes of the boil or even at strike-out when the wort is taken from the burner. Actual chromatographic analysis indicates that hops added at this stage impart nothing good to the beer, and can even impart off flavors at worst (See De Clerck and Fix). This observation by two noted brewing scientists is very controversial, and goes against decades of “official method”.

If you want a beer which has a strong aroma of hops, then you should dry hop. Dry hopping is adding more hops after primary fermentation has finished. If you add these hops during primary fermentation, the gasses generated drive off the hop oils as well. To dry hop, just leave the hops in the secondary fermentation vessel for up to a week, before bottling or kegging (or place them in the keg itself). Traditionally dry hopping was done in a cask that itself was consumed quickly. The effects of dry hopping fade (quickly with pellets and slowly with whole hops).

Hop Form: Pellets & Whole Hops
Pellets
The process of making pellets involves grinding the hops into a powder and pressing the pulp into tight pellets. This process both heats and breaks open the lupulin glands, a result which has two effects:

1. it makes the hop oils available for the beer, so more bittering power can be extracted per unit than can be extracted from whole hops;
2. it damages (possibly destroys) some of the oils, perhaps most noticeable in aroma and flavour (at least some people think they notice a difference in quality)

Hop cones whole and compressed

For many brewers the fresh whole hop flower (more correctly called cone) is the most exquisite form of the hop. If flavour and aroma are important, then whole hops are a nice addition. These fresh hops (often wrongly called “leaf” hops) are sold in two forms:

1. Whole hops which are simply the hop cones packaged in oxygen proof bags and frozen.
2. Hop plugs which are the latest in hop packaging. Here the hop cones are pressed into a plug (14 grams, or 1/2 oz), and this plug expands into the whole cone form when placed in the wort. The lupulin glands are not broken, and the cone is not heated greatly, so the delicate oils remain very fresh. The compression of the plug also helps to prevent oxidation of the hop itself by reducing the surface area exposed to ir. Many people consider these plugs to be the finest, most useful, form of the hop cone, a form which combines the quality of the whole hop with the stability of the pellet.

Hop Storage
Considered on a cost per gram/ounce basis, the hops are possibly the most expensive part of your beer. They also play such an important role in the final flavour and character of your beer that you’ll want to make sure they are in the best possible condition.

Unfortunately, hops are delicate things and suffer damage from various sources, as well as natural and inevitable decomposition. Briefly, there are three important factors affecting hop storage: temperature, oxygen, and light.

• Light is rather easy to control once you buy some hops –just keep them in the freezer. If your hop supplier lets them sit on a shelf under florescent lights, or even worse in sunlight, you might want to reconsider a purchase.
• Oxygen is the second most important factor to control. Hop oils spoil in the presence of oxygen, i.e., the go rancid over time. Hops must be stored in anaerobic conditions which are usually attained by vacuum sealing in plastic that does not leak oxygen, or in bags filled with nitrogen gas. Vacuum packs are sometimes called “hard packs”, and the nitrogen gas bags, “soft packs”. Some places claim that anaerobic conditions are more important for storage than temperature, but that would seem to be incorrect. Garetz in his book Using Hops demonstrates very carefully that temperature is more critical than anaerobic conditions. (This book is the single most useful book on hops for the home brewer. I highly recommend it, if you are interested in any aspect of hop usage)
• Temperature is the single most important factor affecting hop storage. Hop varieties degrade at different rates, and a base rate of degradation for a given hop is determined by measuring the percentage of alpha acid remaining after storage of 6 months at a temperature of +20C. For example, a poor storing hop such as Cascade will drop its alpha acid count by roughly 50%, while a good storing hop such as Challenger will drop only 15 or 20%.
  The rate of alpha acid breakdown is cut about in half for every 15C drop in storage temperature. So Cascade stored open to air at +20 will be ruined in 6 months (50% of the original acids have gone off), while at -20 this same package will still have about 65% of its original alpha acid level.

  If temperature and oxygen are both controlled, then the hop oils remain stable over a long period of time. Cascade stored near -20 under a vacuum, for example, would drop its alpha acids levels by only 15% after 2 years!. If a good storing hop is held at -20 under a vacuum for 2 years, it should suffer only a 5% drop in alpha acids (it would be very difficult to detect such a drop, especially when we consider the many factors which influence hop utilization).

  Once your oxygen proof package is opened, place the hops in an airtight container such as a jam jar, and keep them in the freezer. Even poor storing varieties like Cascade will remain good for many months.