Last night I did an experiment on a supermarket. I'll be interested to see the results in a few days' time.

I usually shop at the Coldhams Lane Sainsburys, which is on my direct route home from work. One of the many things I buy there has, for some months now, been cartons and cartons of grape juice, because I tried a great many fruit juices and decided that it's by far the nicest.

Last month Sainsburys went into Christmas mode, which involved turning an entire aisle into Christmassy tat and squashing its previous contents into what was usually the fruit juice aisle. Some products therefore disappeared from each of the two compressed sections, and my beloved grape juice was among them.

I was somewhat put out by this, but kept my temper, and went and politely asked Customer Service if I could persuade them to rethink the precise set of product lines they were discontinuing over the Christmas period. I can't, for example, believe that that many people prefer carrot juice to grape juice. I've tried carrot juice. I suppose it takes all sorts and a few people might acquire a taste for it, but more people than like the obvious sweetness and freshness of grape juice? It just doesn't make sense to me.

The customer service person was sympathetic to my plight but was unable to help, because she couldn't find grape juice in the product database at all. We conjectured that it might have been discontinued across all Sainsburys, which I suppose would be more convenient for them because their manufacturing side (it was own-brand) could actually stop producing it completely for a few months. So I muttered a bit, and went away, and eventually discovered that the Asda down the road still sells grape juice. And there the matter rested.

Or rather, there the matter would have rested, if it hadn't been for the fact that last week I was sitting in a line of traffic queueing for the Coldhams Lane roundabout, and through my passenger-side car window I could see through the window of the Sainsburys petrol station. Specifically, I could see the petrol station's fruit juice shelf. And guess what was on it?

So. Either the customer service person's database was malfunctioning and grape juice is still available from some part of the greater Sainsburys organism, or that was simply left-over grape juice from the month before last when they were still stocking it. I managed to find the same customer service person, who remembered me, and she was as baffled as I was and unable to shed any light on the question. That only left one way to find out; so in a spirit of scientific enquiry, I went into the petrol station last night and bought all the grape juice they had. Next week, if I remember, I'll see if they've managed to get some more, and if so then I'll go back to the customer service desk and say ‘ah-ha!’.