Hops

Alpha acids: bitterness

Hop alpha acids are insoluble and without bitterness until they are isomerised by heat: it takes the boil, and time. The earlier the addition, the higher the bitterness; after 60 minutes, most of it is done (about 25 to 30 % of the alpha acids have been isomerised in a wort of average gravity). The alpha acid content ranges from 3 % (Saaz) to 18 % (Magnum, Columbus, Warrior) and changes every year with the harvest: redo the calculation with the figure on the packet you bought. The Tinseth formula, used by the IBU tool, gives the bitterness according to weight, alpha, time, volume and wort gravity (the denser the wort, the less the hops isomerise). Guideline: 30 g of a 6 % hop for 60 minutes in 20 litres at 1.050 make about 22 IBU in pellets.

Essential oils: aroma

Aroma comes from the oils (myrcene, humulene, caryophyllene, farnesene and hundreds of minor compounds), which evaporate in the boil. Hence the rule: bitterness at the start, aroma at the end. An addition at 15 minutes keeps a little aroma and still gives bitterness; at 5 minutes or at flame-out, mostly aroma; in a whirlpool at 80 °C for 20 minutes, aroma and a little bitterness (the IBU tool takes it into account); as a dry hop, aroma only (see getting your dry hop right). An "aroma" hop has more oils (1.5 to 3 ml per 100 g) than a "bittering" hop (0.5 to 1 ml), but any hop can do both.

The forms

The main families

Storing hops

Hops lose their alpha acids and oils with heat, air and light. A vacuum-packed or nitrogen-flushed packet, in the freezer, keeps most of it for two or three years; the same packet open in a cupboard has lost 30 to 50 % of its alpha in six months, and smells of cheese. Once open: squeeze out the air, reseal tightly, put back in the freezer, and use it within three months for a dry hop. Producers give a storage index (HSI): high-alpha hops and noble varieties keep less well than average. An aged hop is still fine for bittering, with a higher dose, not for aroma.

Dosing

• First set the style's IBU (the list of styles) and the wanted BU:GU ratio (creating your recipe).
• Split it: 50 to 70 % of the IBU from the 60-minute addition, the rest from the late additions; the IBU tool calculates each addition, the boil schedule tool gives the times.
• Aroma at the end of the boil: 1 to 2 g/L for a pale ale, 2 to 4 g/L for an IPA, on top of which comes the dry hop.
• Fresh harvest hops: 5 to 6 times the planned weight of pellets, at the end of the boil only, unknown alpha.

Replacing a hop that is out of stock

For bitterness, any neutral hop will do, correcting the quantity by the ratio of alphas: 30 g at 6 % are replaced by 18 g at 10 %. For aroma, you look for the same family and similar oils: Cascade by Centennial or Amarillo, Saaz by Tettnang or Sterling, Citra by Mosaic or Galaxy, East Kent Goldings by Fuggles or Styrian Goldings. The hop substitution tool gives the matches and recalculates the quantity; the ingredient equivalences classify hops by use, aroma, origin and alpha, and know which ones are on sale in the shops.