Scientifically Sweet: Classic Fresh Strawberry Jam

Friday, May 21, 2010

Classic Fresh Strawberry Jam

This jam has three ingredients:

Lemon juice
    What? No pectin? Well....ya! No added pectin. There's plenty of pectin in the cell walls of the berries themselves, so why not just extract it and do things the old fashioned way?

    Jam is a type of spreadable fruit gel. It acts as a preservation method due to the added sugar which tightly binds water released from the fruit during cooking and thus decreases the water activity (i.e. the amount of water available for microbial growth). Although some may be tempted to skimp on the large quantity of sugar used in a jam recipe in an attempt to save calories, I strongly advise against it! The added sugar not only serves to increase the product's shelf life, but it is vital in the development of a gel structure. It must be present at a very specific concentration in order to produce the right consistency. So, don't fool around. Jam is serious business. Really serious. Haha...

    The crystal clarity and firm structure of fruit gels is due to a compound called pectin which is naturally present in the cell walls of most fruits. A "gel" refers to a network of cross-linked molecules that entrap an aqueous solution, such as water and its solutes. Pectin, a long-chain molecule composed of sugar subunits, will only form this network in the presence of acidity and a high concentration of sugar. But it’s not that easy. The pH, or acidity level, must be around 3.0 (or 0.5% acid by weight), while the final sugar concentration must be between 55 and 65%.

    To make jam, pectin must first be extracted from the fruit’s cell walls. This is accomplished by cutting the fruit into small pieces and heating it slowly in a saucepot. Pectin molecules gradually dissolve into water that is released from the fruit during heating. To re-build the pectin structure, a large proportion of sugar is added (45 to 50% by weight) to bind water between pectin molecules, thus bringing them closer to one another for optimal interaction (sugar is hygroscopic, and if you’re a regular reader of my blog, then you definitely know that by now). The mixture is then brought to a boil to evaporate some of the moisture and concentrate pectin.

    An acid solution is then added, such as lemon juice, to neutralize or remove the negative electrical charges of pectin molecules so that they can finally unite at specific zones and create a gel. When pectin molecules are initially extracted from fruit cell walls, they adopt a negative charge which causes them to repel one another, making it impossible for them to come close enough to form a gel.

    Boiling the mixture to about 220°F indicates that the sugar concentration has reached 65%. This is the same concept that applies to making fudge. The boiling point of a sugar solution increases proportionally to its sugar concentration.....I'll go deeper into this science next time a make a batch of fudge. If you don't have an instant-read thermometer, or a candy thermometer, well then go get one. Haha, kidding. You can still make jam by monitoring the rate of drip of a dab of jam down a tilted plate. It is ready when it drips very slowly and appears quite thick.

    This recipe makes just enough jam to serve with your fresh Strawberry Ginger Honey Scones. If you would like to make a larger batch, you can double, triple or quadruple the recipe, but be sure to do it very precisely.

    Homemade Jam:
    4.5 oz hulled, chopped strawberries
    4 tbsp (2 oz) sugar
    1 ½ tsp lemon juice

    Place chopped strawberries in a small saucepot over medium heat. Cook until they begin to release some liquid, about 3 minutes. Stir in sugar and bring mixture to the boil. Cook the mixture for about 3 minutes and then add the lemon juice. Continue to boil, stirring often, until the mixture registers 220 degrees F on a candy thermometer, about 15 minutes. The mixture will be very thick yet spreadable. Let cool completely to room temperature. Store in an airtight container in the refrigerator for about 2 weeks.

    For an extra special treat, drizzle fresh scones with some cream cheese know you want to.

    Cream Cheese Icing:
    2 oz (¼ package) cream cheese
    1-2 tsp 35% whipping cream
    ¾ cup icing sugar
    1/8 tsp salt

    In a medium bowl, beat cream cheese with 1 teaspoon of whipping cream until smooth. Beat in icing sugar and salt. Add another teaspoon of cream as necessary so that the mixture is still thick but of drizzling consistency.

    COOK'S NOTE: To make a firmer jam, supplement with some citrus peel, such as orange or lemon. Citrus fruits and apples are especially rich in pectin and can be used to fortify jams made from berries.
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    1. Can I make this with stevia?

    2. Can I make this with Stevia?

    3. You cannot make jam with stevia unless you use additional pectin since jam gets its gel structure largely from the water-binding properties of sugar. If you do wish to make a low calorie jam using stevia, you will have to add pure pectin or carageenan which you may be able to find in specialty food stores. These substances are natural and have very good water-binding properties. Let me know how it works out!

    4. Hi Christina, your blog is fantastic! Can you tell me why you don't add the lemon juice earlier? Thank you.

    5. If the lemon juice is added too early in the process, its acidity could potentially bread down the pectin molecules, resulting in a weaker structure. It would still work, but the texture of the jam would not be as firm and cohesive.

      Thanks for your question and curiosity!

      Christina :)

    6. Thank you Christina!

    7. I'm going to use this recipe to make jam for a woman who recently visited us here in Southern California and couldn't get enough of our fresh, locally-grown organic strawberries. She is 86 and has grown/canned all of her life, but has never made strawberry jam. I'm going to experiment with Stevia if I feel brave.
      Also, I teach high school Biology and I'm thinking about having my students make this recipe in lab and then learn about the molecules, chemical reactions and cells...that's fun and relevant, particularly if we can use something besides tons of thank you!

    8. Saraburns2000 - that's wonderful! I'm so glad you've found this post helpful. I think that is a fantastic lesson for your students. Kids need to learn that there is a Science related to food production. We need more teachers like you out there.


    9. So as a general rule, the fruit:sugar ratio is 1:0.5 i.e. 2:1? I'm looking to make jams without a recipe.

      Just stumbled upon your blog and absolutely love it; will be "visiting" more often.

    10. The long term health benefits from a regular juicing regime are phenomenal. Virtually every health authority recommends that we get 8 servings of vegetables and fruits per day and very few of us actually get that. Juicing is an easy way to guarantee that you will reach your daily target. cold press juicers to buy online


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