One of the great unanswered questions in the history of beer is why it took 9,000 years or so after brewing began for brewers to start using hops.
Today there are very few beers made without hops. They give beer flavour and, most importantly, they keep it from going off. The shelf life for unhopped ale can be as short as a fortnight or so before it starts to spoil and sour. Hopped beer can last for years. But it took many millennia for brewers to discover this, though they had been using a huge range of other plants to flavour their ale in the meanwhile: the bushy, aromatic moorland shrub bog myrtle, for example, the grassland weed yarrow, the hedgerow plant ground-ivy, even rosemary and sage.
The first documented link between hops and brewing comes from Picardy in Northern France, in 822, where Abbot Adalhard of the Benedictine monastery of Corbie, in the Somme valley near Amiens, wrote a series of statutes on how the abbey should be run. The many rules covered areas such as the duties of the abbey’s tenants, which included gathering of firewood and also of hops – implying wild hops, rather than cultivated ones. Adalhard also said that a tithe (or tenth) of all the malt that came in should be given to the porter of the monastery, and the same with the hops. If this did not supply enough hops, the porter should take steps to get more from elsewhere to make sufficient beer for himself: “De humlone … decima ei portio … detur. Si hoc ei non sufficit, ipse … sibi adquirat unde ad cervisas suas faciendas sufficienter habeat.”
It is important that the Corbie statutes should link hops with beer brewing, because hops had other uses they might have been collected for: to make dyes, for example (brown dye from hop sap and yellow dye from the leaves and cones). The stems can also be used to make ropes, sacking and paper. Thus any mentions in old documents of hops being collected from the wild, or even cultivated, does not mean automatically that the hops were going into beer
But Adalhard’s statutes do not say whether the hops were being used to preserve the beer, or merely to flavour it (the way brewers today dry-hop their beers). Proof that hops were being used the way they are today, as a preservative, does not come for three more centuries, at another Benedictine establishment at Rupertsberg, near Bingen, in the Rhineland. About 1150, Abbess Hildegard of Bingen (1098-1179), mystical philosopher and healer, published a book called Physica Sacra, which translates best as “The Natural World”. Book I, Chapter 61, “De Hoppho”, or “Concerning the hop”, says of the plant: “It is warm and dry, and has a moderate moisture, and is not very useful in benefiting man, because it makes melancholy grow in man and makes the soul of man sad, and weighs down his inner organs. But yet as a result of its own bitterness it keeps some putrefactions from drinks, to which it may be added, so that they may last so much longer.”
By itself this does not prove hops were used in beer, just “in drinks” (in potibus in Hildegard’s original Latin). But in a later chapter, on the ash tree, the abbess wrote: “If you also wish to make beer from oats without hops, but just with grusz [gruit], you should boil it after adding a very large number of ash leaves. That type of beer purges the stomach of the drinker, and renders his heart [literally ‘chest’ or ‘breast’] light and joyous.” Clearly Hildegard knew about brewing beer with hops. The passage also suggests that Hildegard knew about boiling wort, without which just adding hops is not much help in keeping away “putrefactions”.
What probably kept the usefulness of hops from being discovered for so long is that the bittering, preserving resins in hop cones are not very soluble, and the hops need boiling for a long time, around 90 minutes, for what is called isomerisation – the physical change in the hop acids to a more soluble form of the molecule – to take place. Nobody would have boiled hops that long, and thus discovered the isomerisation, without a prior good reason (it takes a lot of fuel, a precious commodity when you have to gather wood by hand, to boil quantities of water for an hour and a half). How was it found out that a good long boil improved both the flavouring and the preserving ability of hops? One possibility is that a dyer, boiling hops to dye cloth, made the discovery that the dye water had a pleasant bitter taste, and told her friend the brewer. But this is just a guess.