sealing jars for jam making

I'm not sure whether this has been covered elsewhere - I saw a thread (possibly on the allotment group I belong to on facebook) about sealing jam jars. I was initiated by my mother in the mysteries of little waxed discs and cellophane covers, and thought this was The Way to seal jars of homemade jam properly. In the thread I recently saw, everyone who contributed scorned the aforementioned waxed discs and cellophane covers, and said that they sterilized the old lids from the (reused) jars, and screwed them on nice and tight. No-one had ever had problems with mould. Is this what everyone else is doing? Am I alone in using the arcane cellophane circle method? What does everyone think?

I've made jam for 40 years and never used the cellophane! It's because it's a pain when you use the jam and can't find a lid to fit. I do use waxed discs and a plastic screw on lid. I've never sterilized a lid but they have always been through the dishwasher. I do sometimes get a small amount of mould with plums and gooseberries but just lose the top half inch of the jam and the rest is fine.

I am a bit of a beginner with jam, so I did what my dad used to do with the disk of waxed paper, but re-used the original jar lids after pouring boiling water over them. No mould so far.

But - I think that it stands to reason that if hot jam goes into a sterile jar, with a sterile lid, the waxed paper can do nothing much more than be a potential source of contamination. I should be brave enough to try without on the next batch !

CH wrote:the waxed paper can do nothing much more than be a potential source of contamination.

Ooh, I've never thought about that. The mould is always around the edges of the waxed paper. I might have a go without as well.

This is how I have always understood it (but might be completely wrong of course):

I thought that traditionally, jars of preserves were sealed from the air using melted wax. Presumably covered with a cloth as well to stop insects getting in to the wax. I've always assumed that the waxed paper circles are a rather poor extension of that practise, and are just to prevent the surface of the preserve from drying out, which it can do even with an airtight cover.

I used to use the paper circles and cellophane, to make an airtight seal. But since the advent of jar lids that contain a rubberised seal, I've abandoned them. Providing you put the lid on the jar when contents are hot, the air in the jar cools and therefore shrinks, creating something of a vacuum and keeping the lid completely sealed. As it's completely airtight, I don't bother with the paper circles. I've never had mouldy preserves using this method, although have had some develop on an opened jar.

Thanks - I'm going to try that next time. It would be interesting to seal two identical jars of jam using both methods, keep them for a year and see what happens. Two questions - Ploshkin: the plastic screw-on lid; is that something you've bought? And Freebird: do you sterilize the lids with rubber seals in any way? I usually wash the jam jars in hot soapy water, drain, then heat up in a low oven to sterilize. Would this be OK for a lid, or would it ruin the rubber seal?

I just wash the lids, Dandelion. I've never tried sterilising them. I tend to take the view that if the produce is quite acidic (and for most jams, marmalade and chutney it will be), nasties are going to struggle to take a hold.

I made a batch of rhubarb and vanilla jam yesterday, and sealed the jars using both methods, so that I can compare the keeping qualities. I see what you mean about the hot jam cooling Freebird - by this morning, the lids I had screwed on yesterday had contracted. (It was an odd recipe - the rhubarb, vanilla pod and jam sugar had to be stirred around until the sugar had dissolved, but there was nothing to actually dissolve it in. I lost my nerve, and added a tablespoon of water, after which it was much easier!)

Just to add to the waxed paper disc discussion - I have just read a claim that the purpose of the waxed paper is that the wax should melt and float on the jam, forming a close and airtight seal. Whether it does or not, or if it is needed of not, I am still not sure !

I don't think there is sufficient wax on them for that - not the ones I have anyway. When I get to use a jar of something that I have used a wax disc on, there is usually just a soggy bit of paper on the surface