Why Put a Bitter Flower in Beer? Preservation First and Flavour Afterwards

The useful part is the female flower cone, which contains small glands packed with resins and oils. The resins include compounds that are only mildly bitter as they are and that rearrange when boiled into a form that is intensely bitter and that also inhibits certain bacteria, particularly those that would otherwise sour beer. The oils are volatile and supply aroma, and because they are volatile they boil away, which is the central practical fact about using hops. Tannins in the plant material also help precipitate proteins during the boil, which clarifies the beer. The plant is a climbing perennial grown on tall trellises, and cones are harvested once a year and dried immediately.

Timing determines which of the contributions is obtained:

• •Early in the boil, for an hour or more, which extracts bitterness and drives off aroma
• •Late in the boil, which preserves more aroma and contributes less bitterness
• •At the end with the heat off, steeping in hot wort, which is aroma with almost no bitterness
• •After fermentation, called dry hopping, which contributes aroma and no bitterness at all
• •First wort hopping, added before the boil begins, which is said to give a smoother bitterness
• •Continuous additions throughout, used for particular styles

Beer was flavoured and preserved for centuries with mixtures of other herbs, and the change to hops was gradual and contested. Hopped beer appears in continental European brewing from the medieval period and spread to England considerably later, with the two words beer and ale distinguishing hopped from unhopped drink for a period. The advantage was keeping quality, since hopped beer survives transport and storage far better, which mattered enormously for trade and for supplying ships and armies. Resistance came from producers of the herb mixtures, which were taxed and controlled in several places, and from drinkers accustomed to the older taste. Regulations including the German purity law of 1516, which permitted only barley, hops and water, entrenched the change legally.

Brewing quantifies hop contribution with a specific measure and its limitations are worth knowing. Bitterness is expressed in units corresponding to the concentration of the transformed resin compounds in the finished beer, measured by extracting and reading the absorption of light, and the scale runs from a handful for mild beers to well over a hundred for the most aggressive styles. The measure is objective and correlates imperfectly with perceived bitterness, since sweetness from residual sugar masks it substantially, so two beers with identical figures taste quite different if one is fuller bodied. The compounds also degrade over time, so the measured figure falls as a beer ages. Calculating the expected figure from a recipe uses formulas that account for boil time, wort density and hop content.

Hop breeding has transformed brewing within living memory. Traditional European varieties are relatively low in bitter compounds and carry aromas described as herbal, floral and spicy, and were selected over centuries in specific regions whose names attach to them. American breeding from the late twentieth century produced varieties with far higher bitter compound content and with strikingly different aromas, including citrus and pine notes, which made possible the assertively hopped styles that spread worldwide from the 1980s and which now dominate craft brewing. Breeding continues aggressively, with new varieties released regularly and marketed on aroma descriptors. Supply is concentrated in a few regions with the right day length and climate, which makes the crop vulnerable to weather and disease in those places.

Resins in the flower become intensely bitter when boiled and inhibit the bacteria that sour beer, while the aroma oils are volatile and boil away, so timing decides what is obtained. Long boiling gives bitterness and additions after fermentation give aroma alone. Hops displaced herb mixtures because hopped beer survives transport, which mattered for trade rather than for taste.