Ask Peter: Frozen fruit for jam and baking
I have been given loads of frozen, ripe, whole plums. I have made all sorts of things but would now like to make some jam. Could you please tell me just how I go about weighing the plums so I can add the correct amount of sugar? I think, if I weighed them frozen, I would probably get too much liquid. But how can I weigh them thawed without losing too much liquid? Should I thaw over a bowl and save some of it? I would appreciate your advice as I made jam with the same plums when they were fresh and it was delicious.
Scientifically speaking, the amount of liquid in a kilogram of fresh fruit or vegetables, versus frozen, is identical. The difference is that if you were to use frozen fruit in something like a muffin or cake, the liquid that will ooze from the fruit can affect the finished baked goods, making them soggy. As the fruit defrosts the cell walls, both internally and externally, break down so liquid which otherwise is held within the cells, leaks out. I've successfully made muffins using snap-frozen individual raspberries (I add them to the mixture still frozen). But less successfully, when I once tried to roast some previously frozen pumpkin for a chunky risotto, the pumpkin flesh had become watery and fibrous at the same time.
The planned chunky risotto was instead presented as a slightly smooth pureed pumpkin and al dente rice affair. Still tasty (flavour wasn't lost) but not what I'd intended. Likewise an upside down plum cake I made ended up with a soggy bottom (then top) when made from frozen fruit. So the next time I made it, I defrosted and drained the plums before putting them in the cake tin. I simmered and reduced the defrosted juices with a little honey and orange juice which I used to glaze the finished cake.
When making your jam you can drain the fruit in a sieve or muslin if you like, and use this weight to decide on the ratio of sugar to use. By draining the fruit before weighing it you will likely increase the flavour profile of the jam as you've simply removed "water" from the fruit (in the same way that dehydrating fruit also increases the intensity of the fruit). You may find you need to add a little extra lemon juice or similar to counteract the increased sweetness. Or you may find that the end result is so good you'll never use fresh fruit again.
Unlike the plums you have, likely to have been grown by a friend, some commercial frozen fruits are lacking in flavour because they are usually harvested before optimum ripeness as picking, grading and snap-freezing is easier to handle if the fruit is less ripe and therefore more firm. Bear this in mind when making jams, as you may find adding spices (fresh or candied ginger, lightly toasted cloves, star anise or cinnamon etc) is a good way to add character to finished jam if the fruitiness is lacking.
On the other hand most commercial fruit purees seem to be made from perfectly ripe fruit, because squashed fruit in a factory situation isn't such a problem when making a puree. If my fruit jams, sauces or compotes don't taste as fruity as I'd like (especially in winter) then I'll add some frozen puree. If using commercial purees check the ingredients as some do contain a lot more than just the fruit.
Talking of dehydrated fruit, currently on the menu at dine by Peter Gordon I have a dessert which features meringue fingers flavoured with strawberries. I was keen to have an intense and slightly pink meringue and it was obvious that the only way to do this was to mix crushed, sieved dehydrated strawberries into the meringue mixture before piping. I sprinkled the bits that didn't go through the sieve on top of the meringues and baked them as usual. What I ended up with were slightly fruity aromatic fingers that really added the wow factor to a dessert that also features strawberry ripple ice cream and raspberry puree. Fabulous!
I use dehydrated strawberries from Fresh-As' terrific product range - I wish they were available in Britain (see fresh-as.com for local stockists).
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