"When in Rome", the saying goes, "do as the Romans do". It is purely for this reason, mutatis mutandis, that during spells of warm, sunny weather in the Rhine Valley, Weather Eye feels obliged to view the mysteries of meteorology through the amber luminescence of a cool Teutonic brew.
In a corner of a German garden, inspiration sits at my right elbow in the form of a cold, frothy glass of German beer. Soon, Tennyson's The Brook comes to mind. This vocal stream, you may recall, had autobiographical pretensions and began by announcing:
I come from haunts of coot and hern,
I make a sudden sally;
And sparkle out among the fern
To bicker down a valley.
A more interesting verse, however, comes a little later:
I wind about, and in and out,
With here a blossom sailing;
And here and there a lusty trout,
And here and there a grayling.
Now, the reason why trout and salmon find brooks like Tennyson's attractive is that they are cool and rich in oxygen. The amount of oxygen that can be dissolved in a given volume of water is related to its temperature; the colder the stream, the greater the amount of oxygen the water holds, and therefore the more appealing it is to lusty trout and grayling.
Which brings us back to beer. The substance which gives a beer its distinctive, tasty fizz and pleasant froth is carbon dioxide. In real ales of the kind the English are so fond of, CO 2 is generated by the action of yeasts on residual sugars in the drink; in the case of the more common beers and lagers, however, the gas is added artificially either at the brewery or when the glass is being filled. Either way, the beer resembles Tennyson's brook; the colder the beer, the more CO 2 can be accommodated in it.
And therein lies the explanation why my beer has gone flat and lost its fizz. In cool surroundings, dissolved CO 2 is gradually released over a long period in the form of bubbles rising to the surface. But on a hot, sunny afternoon outdoors, the beer warms quickly; it can hold much less CO 2 than it could if it were cooler, and the whole process of expelling the carbon dioxide is accelerated.
The end result, quite quickly, is a flat, sickly, lukewarm liquid with not a trace of froth on top.
There are two cures for this unpleasant and potentially recurrent ailment: drink faster - or drink your beer in a much cooler place.