Thermometers

I've just finished making marmalade, batch number 3, and noted that yet again, it was ready before reaching the 'jam' setting on the thermometer.

A couple of years ago I bought a potting shed. I thought it might be good for overwintering some salad crops, as my greenhouse is rather draughty. Over my gardening career, I've accumulated four max/min thermometers, so thought I could compare the greenhouse with the shed to see which was the warmer. I noticed that none of the four thermometers was reading the same temperature, so took them indoors to test them, at ambient house heat and in the fridge. Not only did they all read differently, but there wasn't a set difference between any of them - so one that I thought to be fairly accurate in the fridge would not be so at a warmer temperature. A couple of thermometers that were 2 degrees apart in the cold, might be 5 degrees apart in the warm. Overall they differed by up to 7 degrees from each other. Not helpful if you want to know if the temperature has been below freezing.

All this leads me to think that it can probably be applied to domestic jam making thermometers too. I guess that manufacturers don't rate accurate calibration too highly for home-use implements. So if you are relatively new to making marmalade or jam, or have problems with setting, use a thermometer if you wish, but don't assume that it is perfectly accurate. As I suggested in the New Years Resolutions post, use other methods too.

Hmm. I found this too. I checked my thermometer against boiling water - so 100C, and it was a bit out. Explains why my first batch of apricot jam was rather solid ! My excuse anyway   

I had a standard 'jam' thermometer but I left it in a pan to keep a check on the temperature when cooking a ham & found that a lot of the numbers marked on the metal back disappeared - a thermometer without numbers is less than useless. I've got a digital probe thermometer now that I used when I made my marmalade. I doubt that domestic ones are any more accurate than non digital but I did my marmalade to 104.5 & got a good set. I have also used it for fudge with good results so it seems to be within a gnat's crotchet of what it should be.