I searched the Internet for candidate recipes for red raspberry syrup and I found only one recipe that made any sense to me. I made the syrup using my kitchen equipment to separate the juice and pulp from the seeds, and otherwise followed the Internet recipe as a first attempt at making a great seedless red raspberry syrup. I concluded that the recipe was pretty good though rather in error about the degree of thickening provided by the given procedure.
I've decided to provide the simple recipe I found and also discuss ways to improve it. Specifically, I am embarking on the use of thickeners that are used commercially, especially in high end restaurants, to create syrups, sauces and pastes of varying thickness. I have created a Food Nirvana entry for using thickeners and located it in the Technology section following the Dabbling in Science topic. You can refer to the thickeners entry for more information.
Now let's proceed with this very simple recipe. Simple? Well, at least there aren't many ingredients. Processing, however, is easy or hard depending on whether or not you have a Kitchen-Aid® stand mixer with a Food Mill attachment. If you don't, then you have to process the raw or frozen fruit with the alternative methods I describe.
Okay, let's proceed ...
Ingredients: (makes three or four cups of syrup)
6 cups of fresh or frozen red raspberries
2 cups of water
1 cup of sugar
Optional Ingredients: (Use your high sensitivity electronic kitchen scale)
4.0 grams of Agar Agar
2.4 grams of Kold-Kiss® concentrated sodium benzoate solution
Fruit Processing Directions:
If you have fresh berries then freeze them first and then thaw them. Freezing helps to break up the cell structure to make the later extraction of the pulp and juice relatively easy. They can best be thawed in the microwave oven to a slightly warm temperature. Note also that if the dish is covered with plastic wrap the fruit can be brought to a boiling temperature in the microwave oven, and that really makes later separation of the juice from the seeds easy, with or without the Food Mill attachment described next.
If you have the Food Mill attachment described earlier, use it to separate the pulp and juice from the seeds, and then discard the seeds.
If you do not have the Food Mill attachment described earlier, you can process the berries on slow to medium speed in a bowl using a stand electric mixer for about three minutes. That helps to separate the seeds from the pulp and juice. Then put all of that mixture into a large fine mesh sieve over a large bowl and stir until nothing is left in the sieve except seeds and pulp. Then press on the pulp and seeds with a small spatula or the back of a spoon to get the pulp to go through the sieve, rubbing across the pulp and seeds fairly firmly, multiple times, until only the seeds and a tiny bit of pulp remain in the sieve. Discard the seeds and residual pulp.
Now follow the directions below for making the syrup.
Syrup Directions "without" the optional thickener:
Put two cups of water, the sugar and the processed fruit juice and pulp into a two quart saucepan.
If you are using sodium benzoate then measure out the correct amount and add it to the saucepan and stir to mix the ingredients.
Heat the mixture on high until it boils, then reduce to heat to low to result in a very low boil.
Boil the mixture for up to 30 minutes to reduce the liquid volume to three cups and in the process somewhat thicken the syrup.
Pour the syrup into three, eight ounce canning jars and seal them with the canning jar inserts and rings tightly. I use a wide mouth funnel inserted sequentially into each jar to assure the top of the jar does not get messy with the syrup during the pouring process.
You now have a light to medium thickness syrup that is fine for later use on pancakes, waffles or ice cream.
At this point you want to process the canning jars in a boiling water bath for five to ten minutes, then remove the jars and retighten the lids. You can store the jars in your food pantry, but once opened refrigerate any unused syrup.
Alternatively, you can tighten the lids on the jars and let the contents cool to room temperature. Typically the jars will develop a vacuum and seal during cooling. If not, then use your commercial vacuum sealer by slightly loosening the jar rings, vacuum sealing the product at a vacuum level of 25 inches of mercury, and then retightening the rings.
Note that vacuum sealing the syrup when it is very hot is a bad idea as it will boil out of the jars and make a mess. Note also that refrigerator storage is recommended rather than pantry storage, though with the sodium benzoate preservative in the syrup pantry storage of the vacuum sealed product should be okay.
Syrup Directions "with" using the optional thickener:
Follow the syrup ingredients and directions shown above with two major exceptions. Reserve one half cup of the water to use with the thickening agent. Bring the syrup to a low boil and immediately process and use the thickening agent.
Mix the thickening agent with the reserved one half cup of water in a one cup glass Pyrex® measuring cup, stir well and let it hydrate for five minutes, stirring twice during that period.
Heat the mixture in the measuring cup in the microwave oven for approximately one minute to barely bring it to a boil. Stir the mixture to get the thickening agent to disperse evenly. Then add the mixture immediately to the boiling syrup while stirring. Mix thoroughly.
Proceed with the above syrup directions for pouring the syrup into canning jars. You will have four, eight ounce canning jars of nicely thickened syrup instead of three.
Enjoy!