Before I start this post, let me make it clear that it is made purely from my personal observations and on the knowledge acquired through my chemistry O level 40 years ago, and is no way a criticism of any individual brewers or pubs.
These last few months I have come across more than the usual amount of cask beers that have been served in a less than perfect condition. That is not to say that they are warm but that their taste is not quite what I expected, and in some cases verging on the unpleasant. I started to wonder why ?
Discounting beers from newish breweries, many of which I had never sampled before and could not give a really fair opinion of, there are several from established breweries which have disappointed me. Nothing has changed fundamentally. The beer will have been produced in the same way at the brewery in am sure, and the same stringent considerations given to their production; the barrels will have been cleaned in the same way; and the pubs will have the same cellars and dispense the beer in the same way. So what has changed ? It has been sunny and hot for most of the summer months.
Would this change the character of the beer ? One would hope not. It should leave the brewery in the same tip top condition as always. But beer is still a living organism. Yeast is in the beer giving rise to the secondary fermentation that the product requires. Has the hot summer led to changes in secondary fermentation that the brewer cannot foresee ?
Consider a beer leaving the brewery in its cask, from the brewery cool room. It is then transported to the pub for sale. This is where I think the summer begins to play its part. Some brewers are lucky to brew on the site of the pub, and nothing will affect the beer since it has nowhere to be transported. Others have short distances to travel and hopefully the beer will not have time to be adversely affected by the heat. But what about deliveries a long way away.
Again the beer leaves the cool room but is either transported by van to the point of sale, or a wholesaler. The back of a van, on a warm day gets hot, and the beer will obviously get warm too. The yeast will start to work quicker, or harder and fermentation will speed up. The beer is then unloaded and placed in a cool pub cellar, or hopefully a cool room at the wholesaler. Fermentation will slow down again, but the yeast will be 'confused' and maybe its effects are affected (if you forgive the pun!). If it is then transported again on a warm day from the wholesaler, the process repeats itself. Surely this cannot be a good thing for the final condition or taste of the beer.
So, the beer leaves the brewery as the brewer intends, and is served in the pub as the landlord intends, but the middle bit may affect the product, leading to a deterioration in quality of the beer, to alterations in flavour, and to a shorter shelf life. If this is the case roll on autumn, an a return to normal.