First of all, my apologies to Beetroot queen and others for hijacking this thread.
Some background. I have been making apple chutney for about 15 years, using my mother’s very old recipe. I love its taste and also the smell in the kitchen when it’s being made - this very evocative. My first season’s pots were very poorly sealed and lost over a quarter of their weight and darkened a lot. After that, I learned to seal the pots with metal caps, and now I only see some darkening after over a year. This darkening occurs from the top down, and there has been no visible “shrinkage” due to evaporation.
I agree that taste is the most important factor, and this darkening doesn’t bother us at home. I do not intend to sell it, but occasionally I give some away. In these circumstances, I want to offer pots that have a uniform colour. That is one reason for my interest.
The other is that I was a food scientist in a previous life. Fruit and vegetable processing was not my area of expertise, but I am very curious about what is going on here, and why. I do know that browning reactions are very important for appearance, taste and odour in many foods, and these reactions are varied, very complex and not fully understood. I have wondered if the darkening was a result of evaporation, reactions with air (oxygen), some other factors, or a combination of factors. However, this is starting to sound like a science project rather than making chutney.
Thus, I am very grateful to Mrs Bee for sharing vast practical experience, and for the offer of a list of recipe books, which I may take up in the future.
However, this year the scientist in me wins out. Thus, I propose to get better scales and calibrate them. Then I will weigh newly sealed pots and monitor their weights over the coming years to see if weight (water) is lost by evaporation as darkening increases.
[On reflection, I find it hard to believe that this question has not been studied by the likes of Campden Research, and the answer is lying in some library].