Pasteurization of apple juice

My smallish orchard (20 trees) is now in its tenth year, and cropping quite well.  This autumn I had more apples than I have space to store them, so I've been juicing.  With my electric juicer (domestic but quite heavy-duty) I've been getting about 450 ml juice per kg apples.  The juice freezes well, but I soon ran out of freezer space and also wanted a storage method that didn't rely on a continuing electricity supply.  Pasteurization, although it requires an initial energy input in the form of oven heat, seemed like my best option.  Once done, the juice should store for at least several months, kept in a cool dark place (the back of my garage).  Friends who'd done it before got me started, and I researched the method on-line to confirm and expand on the information they'd supplied.


Temperature requirements

The consensus seems to be that the juice needs to be held at a minimum temperature of 70 deg C for at least 30 minutes.   This was what my friends said, and was corroborated by all the on-line references I found.


Jars / bottles

My friends use screw-topped wine bottles, but as I didn't have very many of these I used some tall screw-topped glass jars which had contained passata in a previous incarnation.  Whatever you use, the important thing is that the tops should be undamaged and capable of achieving a good seal.  My metal lids were of the type with a thin rubber / plastic?  sealing strip around the inside of the lip. They also have a raised area in the centre that pings down as the jar contents cool and a vacuum is formed.  That's quite handy as it demonstrates that you've got a good seal, although even flat lids will get a slightly convex look if correctly sealed under vacuum. 

Sterilizing bottles/jars and lids

My jars had previously been sterilized and prior to use, were washed thoroughly in hot, soapy water, then rinsed in hot water. You could also sterilize them by putting them in a hot oven for 10 or 15 minutes, but you'd then need to
let the jars cool before putting cold juice into them.  While the juice was in the oven I left the clean lids soaking in Milton's Solution, the stuff used for sterlizing baby's bottles.  People sometimes use boiling water, but I find cool lids easier to manage. 


Oven Method

I filled the jars with fresh juice and stood them on a roasting tray in the bottom of my oven, without the lids.  I put them in the oven from cold, as I thought the more gradually they were heated the less liklihood of accidents. I then switched the oven on with the temperature set to 80 deg C with the fan.  The jars/bottles need a bit of space around them for air to circulate.   I ended up with 13 and could have fitted 15, but no more.  Although the oven thermostat indicated that the temperature had been reached after about 15 minutes, I felt the jars by hand and was not convinced.  I had over 6 litres of juice that I needed to bring to the correct temperature, and whilst the air in the oven was probably hot enough, the liquid definitely wasn't.  I kept checking by hand, at ten minute intervals, and in my oven it took 70 minutes for the jars to stop getting any hotter.  At this point I left them in the oven for a further 30 minutes (100 minutes in total).

Sealing

I think it's necessary to get the jars/bottles sealed pretty quickly after they come out of the oven.  I lifted the tray out onto a large wooden board, shook the lids dry and screwed them on to the jars pronto.  You have to make sure the jar/bottle rim is spotless, as any bits of fruit fibre could prevent the formation of an air-tight seal. 


Long term storage

I'm not sure how long the juice should last.  Probably at least until the next apple harvest, possibly longer.  I'll do a bit more research and post that information later, plus I'll conduct my own trial here.