The recipes on the pectin packages are formulated to result in a reliable set with their brand. If lemon juice is necessary, the recipe will indicate it. I'm assuming it will be called for, because blueberries are low-pectin and low-acid.

Nothing's foolproof, though. There's been a lot of discussion in the past about recipe failures with commercial pectins. There's always that element of chance.

If you want a really firm set without risking over-cooking, you might try substituting some apple for a % of the blueberries. Apples are great for pectin, especially green ones, and their flavor tends to be pretty neutral, so the end result should still be definitely blueberry.

Carol

Acidity doesn't seem to affect the setting of a jelly or jam as much as the concentration of sugar vs. pectin. The blueberries I grow here, are very acidic and quite sour. The soil blueberries is also very acidic, like about a pH of 4.0 or so. Even though they are cultivated types, my dad planted varieties that were sour to begin with. His hope was to reduce birds that feed off them. If you want a definate set when using an added pectin, I suggest the Pomona brand. It sets up with no concern about sugar. One fruit that is super high in pectin are quince. Because I like making quince jelly, I still have to resort to using a no sugar pectin, as I cannot enjoy all that sugar needed for it to set properly.

Carol,

Blueberries are definitely not low acid, the pH runs a little over 3. I can't speak to the relative pectin content, but the blueberry jam I have made is definitely not a soft set, like peach for example. Blueberry jam sets up really fast.

Petro

I was citing the chart "Acid and Pectin in Fruits and Jam Vegetables" from "The Jamlady Cookbook." However, as she notes, there are so many varieties and differences in growing conditions, pH levels can be quite variable. Also, of course, the ripeness of the fruit is a factor in the pH.

You're fortunate that the blueberries you've been working with have been higher-acidity, just as here in the PNW strawberries are higher in acidity and can set just fine without commercial pectin or over-cooking, though many sources say strawberries can only be set with added pectin.

Cornell's Northwest Center for Food Entrepreneurship says "A pH range of 2.8 to 3.3 is needed to set the gel depending on the nature of the pectin. The most common cause of gel failure is insufficient acid."

Carol

Carol,

I was referring to the numbers provided by the USFDA Center for Food Safety and Applied Nutrition (see link below).

I don't think fortune has much to do with our blueberry jam because the berry sources range all over the map in the last 20 years from semi-local Illinois berries to Wisconsin, Indiana, Michigan and New Jersey berries. While produce characteristics certainly varies depending on growing conditions and varieties, I suspect that blueberries are simply less sensitive than other fruit. As you say, instructions provided with the pectin will let you know if you need added lemon. I can't speak to all the varieties of pectin available. We use Sure-Jell and it does not require any added lemon for blueberries.

Petro

Here is a link that might be useful: pH values for various foods

Gelling using natural pectin in the fruits seems to set better with the more sugar you add. I do know expect that a high acid fruit like a citrus based one, would take a longer time to set properly. Here, I add HollyTone fertilizer to my blueberry bushes as well as adding some elemental sulfur every other year to help keep the acidity very high and pH very low. Without that low pH, the bushes will not grow blossoms or berries.

Right now, my honey berries are ripe and loaded. They look a little like a bright colored blueberry, but with an elongated shape. Mild taste however. The honeyberries don't need the soil to be so acidic.

I made the jam tonight using Sure Jell Low Sugar pectin and it set up beautifully. It didn't have any foam in the pan as I was ladeling into jars but now a few hours later the jars seem to have foam around the edge of the jam. I want to enter this in our Fairs here this year and I think they take points off for foam? Arrgghh! Oh well, it sure set up nice and tastes yummy.

Susan in NC

Try giving the jelly jar a few brisk shakes. It may move the surface a little to help break up some of the bubbles. Its inevitable to have bubbles. One way to reduce that issue is to flip the jars over slowly once or twice while they are cooling.