Here's the thing. How many times have I told my students not to buy supermarket strawberries to make jam? It must be hundreds if not thousands. Strawberries that are grown large and glossy for lovely pavlovas - other desserts are available - generally have a high percentage of water content which isn't a great attribute for making jam. Too much water makes the jam very difficult to set so I usually recommend Pick Your Own fruit to be a better bet. Pick smaller fruit, a small proportion of which should be slightly under ripe. All fruit has the most pectin just before it is ready to be picked - it then diminishes the longer it is kept. Strawberries don't have much of this elusive benefit - it's a form of starch - so if you PYO and then make your jam as soon as arriving home, so much the better.
Anyway, back to me. I saw some lovely strawberries in the week running up to Easter - aha! my customers would love some Strawberry Jam for Easter I thought, and before I knew it I was back at The Old Smithy wondering what on earth I was thinking of. Two attempts at making the jam and getting it to set later, I gave up.
Easter tree house building came and went, back to work, 20 jars of unset Strawberry Jam mocking me from the table. Right, I thought, today is the day. I have some frozen gooseberries so I put 2 kgs in a pan, put them on a low heat to soften and cook. I added just a teacupful of water to prevent sticking. Gooseberries have a lot more pectin than strawberries and would help to make the jam set - hopefully!
Once the gooseberries were soft I emptied the jars of 'jam' into the pan and gave them a good stir to mix. I salvaged all of the jars and washed them in hot soapy water, gave them a rinse and then put them in a warm oven 50-100 deg C to dry and sterilise. I intended to use new lids so that I didn't have any sealing issues.
I realised that I would need more sugar but I didn't know how much. So, using my trusty refractometer - which you all have if producing for sale right? - I took a reading which was 50. As it would need to be 60+ I added 1 kg of sugar, stirred to dissolve, and then took another reading. It was now 55 so I knew that I would need a further 1kg, which kind of makes sense as I had added 2kgs gooseberries. Better to be sure though, as I didn't want a third failed attempt! As all the sugar was dissolved I increased the heat and boiled rapidly for approximately 5 minutes before testing for a set by the cold saucer method. I have an irrational mix of technology (refractometer) and old fashioned customs (cold saucer test) in my kitchen. I have never liked using a thermometer and don't actually own one, I don't think.
All jarred up and, at last, tasty - SET - Strawberry & Goosberry Jam!