This is my favourite of all the marmalades I make and I use ½ lb jars rather than 1 lb jars so that I can put some aside for gifts. This lessens the pain of giving away something I want to eat all to myself.
When choosing your whisky go for the best quality you can afford. If you can, use a good 10 year single malt Scottish whisky from Islay like Laphroaig, Ardbeg, or Lagavulin as they all have a wonderful smooth, smoky, peaty flavour.
Place all the fruit, whole, in a large saucepan. I use my stock pan for this. Cover with water, approximately 5 pints and put a heat proof dish over the top to ensure the fruit stays under the water. Leave the fruit overnight or for approximately 12 hours.
The following day heat the water and simmer for approximately 2 ½ hours or until the grapefruit is very soft and squishy. If any of the grapefruit have split it means they are ready. Leaving the water in the pan, remove the lemons from the water, place on a lipped dish (I use a glass pie dish for this) and roughly chop up. Place all the chopped lemons, including pips etc, in a muslin square or muslin bag. Retain any juices in the bottom of the pie dish or pour them back into the pan.
Remove the grapefruit and cut into quarters. Gently scrap off the pith and pips and put in the muslin with the chopped lemons. Roughly chop the grapefruit peel. At this stage I pour the water into my maslin (preserving) pan, although you can continue to use the same saucepan if you wish.
Tie up the muslin with the lemons, pith & pips in to the inside of the pan with the water in. Add the chopped peel and any juices to the water. Bring the water to a simmer for about 10 minutes.
Lower the heat, remove the bag and place in a bowl. Add all the sugar and stir constantly until it has all dissolved. If you are not sure if it has dissolved continue stirring for another couple of minutes. Take the muslin with the lemons in and hold over the pan. Squeeze the muslin to get out any juices and pectin. Pectin is a white’ish sticky substance. I wear clean rubber gloves when doing this part. Once fully squeezed you can discard the muslin.
Bring up the heat under the pan until the marmalade has reached a rolling boil. I then gently lower the heat until it is just boiling. Boil for 15 minutes - do not stir. You do have to keep an eye on the pan at this stage as if you have the heat too high the marmalade can boil over.
After 15 minutes, remove from heat and test for setting point on a cold plate. This picture is of a different marmalade, but it shows you what any jam or marmalade looks like once setting point has been reached. If setting point has not been reached return to heat and boil for another 5 minutes.
Once setting point has been reached pour in the whisky and stir well. Pour into sterilised jars, put on the lids firmly, but do not over tighten and leave to cool fully before labelling. See my ‘recipe’ for “Preserving equipment & how to sterilise jars and lids”
NOTE: If you are unable to get hold of dark muscovado sugar, use normal dark soft brown sugar and add a couple of tablespoons of treacle (dark molasses).
If you are unable to obtain jam sugar use normal granulated sugar and add ½ a bottle of liquid pectin about 5 minutes before you test for setting in step 6.