Know Your Ingredients: Blueberries

With a nice flavor and spicy aroma, blueberries make a good dry red wine.

First some basics: There are about 109 blueberries in one cup (240 ml), and they weigh about 5.2 oz (148 grams).1 Fresh blueberries keep best when stored cold, just above 32F (0C).2 They keep well frozen, too, and the freeze/thaw cycle helps in extraction.

Citric is the dominant acid, and all titratable acidity (TA) numbers in this post will be as citric. Almost all the sugar is glucose and fructose.

Composition of blueberries


Table 1: Blueberry and grape composition1
Component Blueberries Grapes
Water 84.21 80.54
Protein 0.74 0.72
Fat 0.33 0.16
Ash 0.24 0.48
Fiber 2.4 0.9
Total Sugar 9.96 15.48
Starch 0.03 0


The amounts are g/100 g, and do not add up to 100 because the test for each component is subject to experimental error3. About 5%, by weight, will be refuse – things like stems or unsuitable berries – so either use the data on sorted, stemmed fruit or scale your answer by 95%. To find the amount of sugar in 100 lb of fresh blueberries, for example, multiply by 0.096 (9.96% sugar) and by 0.95 (95% usable fruit). That would be 100 lb * 0.096 * 0.95 = 9.12 lb.

Measuring sugar content

Hydrometer and refractometer readings don’t work well to estimate sugar in raspberries, like they do for grapes. Ever since I found this out, I’ve been wondering about other fruit. What about blueberries? They look more like grapes than raspberries in table 1. Oh, they have more fiber than grapes, and this can make sugar a smaller proportion of soluble solids, but they have only a third the fiber of raspberries. Also, blueberry sugar content is double that of raspberries. Both of those things should mean that your hydrometer or refractometer will get you much closer to actual sugar content of blueberries than they will for raspberries.

Some data to quantify “should” and “closer” in the table below. This is from a study on how peat, sawdust, and cocoa husks affect blueberries, but I was more interested in the brix and sugar numbers they reported:

Table 2: Brix vs Sugar Content in Blueberries4
Substrate Brix Total Sugar Sugar Brix Ratio
Average 14.15 12.11 85.6
Peat 14.45 12.04 83.3
Sawdust 13.95 12.30 88.2
Cocoa Husk 14.05 11.98 85.3

Total Sugar is percentage of fresh weight, and if all soluble solids were sugar, then Brix would equal Total Sugar. The Sugar Brix Ratio expresses sugar as a percentage of soluble solids. What a difference! Sugar is over 85% of soluble solids in blueberries, compared to not quite 30% for raspberries.

How much pectic enzyme for your blueberry wine?

I have seen blueberries listed with “low pectin fruit” in some places. Others have said that blueberries have a “medium” pectin content, and at least one described blueberry pectin content as “high.” I wasn’t able to find reliable numbers, so I fall back on indirect methods. Pectin is a form of soluble fiber, and according to table 1 blueberries have about 2.5x the fiber as the same amount of grapes. Does that mean blueberries have 2.5x the pectin as grapes? I really don’t know, but sometimes you’ve just got to work with what you have. There’s no downside to adding more pectic enzyme than you need, so I recommend using 2.5x the recommended dosage for grapes on your blueberries. Remember to use weight of the fruit and not volume of the must – your blueberry must is likely to contain added water.

Average Stats
Brix: 13.234,6
Sugar (g/100 g): 11.471,4,5
TA (% citric): 0.9374,5,6
pH: No Data
Yield (%): 87.944

Making blueberry wine

Blueberries have more acid and less sugar than grapes, but they are similar enough to make dry red wine. Use the weight of your fruit and the juice yield in the average stats to estimate the volume of juice in your fruit. Don’t worry if you don’t get that yield. Most home winemakers wont, but with time the free run juice and the juice trapped in the pulp will become more similar. At pressing, after several days of fermentation, the juice you leave behind will be very close in composition to the juice you press out.

A hydrometer or refractometer can be a pretty good guide to sugar content of blueberries, so the place to start is with a good clear juice sample – filter with a paper towel, then a coffee filter. Test the specific gravity and titratable acidity, then use the Wine Recipe Wizard for recommendations on how much water and sugar syrup to add.

Say you have 100 lb of blueberries and they test out to the values in my average stats box. That would be about 45 kg, and a 87.94% yield indicates 39.6 liters of juice. A brix of 11.47 is equivalent to a specific gravity of 1.046, and we’ll use the average titratable acidity of 0.937% as citric. I don’t know how you like your red wine, but lets pick a target gravity of 1.090, for this example, and a target acidity of 0.6%. The Wine Recipe Wizard suggests 10.3 liters of water and 12.1 liters of sugar syrup. It says you’ll have 62 liters of must after that, but remember these calculations are juice only – you’ll be fermenting on the pulp so your must will be larger.

Freeze and thaw the blueberries to break the cell walls, release the juice, and allow the yeast to do their work. Ferment your must for 3-5 days, then press. Continue fermenting the pressed wine under an airlock.

Is blueberry wine prone to stuck fermentation?

I’ve read a lot about stuck fermentation in blueberry wine, but I’ve never been able to get anything more definitive than, “lots of people say so.” For the record, I’ve had a stuck fermentation on a country wine style (3-5 lb fruit/gallon must) blueberry wine. It turned out to be a nutrient deficiency. I say that because I got it going again after adding more nutrient and a new starter. Another blueberry wine, made more like a red wine from grapes, fermented out normally and quickly.

If you’re worried about a stuck fermentation in blueberry wine choose a hardy yeast like Red Star’s Premeir Cuvee or Lavlin’s EC-1118. Stay well within the yeast’s temperature range. Blueberry wine lends itself to a red style anyway, and red wines are normally fermented at warmer temperatures than whites. Use yeast nutrient and follow the directions. Keep an eye on pH, especially if you’re making it like a country wine.

Bookmark this page, and help keep it up to date!

The Know Your Ingredients series is a way of collecting useful information on various wine bases. Its the sort of thing I’ve googled for, but couldn’t find, when starting a new style of wine. I hope I’ve saved you some trouble. Nobody’s perfect, though, so if you notice a mistake or something worth adding please leave a comment and let me know. I’d especially like well-sourced data on blueberry pH and pectin content.

Sources

1) USDA National Nutrient Database Great information on the composition of many foods. I used the keyword “blueberries” and the food group “fruit & fruit juices,” and selected raw blueberries to find information for this post.

2) On Food and Cooking – Haraold McGee
This is a book on cooking that every winemaker should have. It’s packed with information on all sorts of ingredients, like blueberries and other fruit. It puts blueberries at 11% sugar and 0.3% acid (a little low compared to my other sources), by weight.

3) Documentation for USDA National Nutrient Database When you really want to know how the USDA determined the amount of fat in raspberries – or how and why they did anything in the nutrient database – look here.

4) INFLUENCE OF SUBSTRATE ON YIELD AND CHEMICAL COMPOSITION OF HIGHBUSH BLUEBERRY FRUIT CV. ‘SIERRA’ – Ireneusz Ochmian, Józef Grajkowski, Katarzyna Skupien
Evaluates the influence of three types of substrates (peat, sawdust and cocoa husk) on yield, quality and chemical composition of highbush blueberries. Good data on sugar content, soluble solids, acidity, and juice yield of blueberries.

5) EVALUATION OF CHEMICAL COMPOSITION OF FRESH AND FROZEN BLUEBERRY FRUIT – Katarzyna Skupien
Studied the nutritional properties of highbush blueberries and how they changed during storage, but I was interested in the total sugar (10.87, 11.83, 11.22, 11.53 % fresh weight) and titratable acidity (0.54, 0.80, 0.81, 0.87 % fresh weight) at time zero.

6) Chemical composition of selected cultivars of highbush blueberry fruit – Katarzyna Skupien.
Compared the basic chemical composition of four varieties of highbush blueberries. These four are tested over three years giving twelve observations of brix and titratable acidity.

Notes and Further Reading

The Average Stats table is just me with a calculator averaging the values in my sources. Real world agricultural commodities vary, but I’ve tried to make this a good starting point.

There are many Brix/Specific Gravity tables on the web. Here is one.

Hopefully your yeast will always ferment out, but if not, here is how I deal with a stuck fermentation.



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6 thoughts on “Know Your Ingredients: Blueberries

  1. Ben

    Thanks for this resource. Particularly the portion on measuring sugar content is really useful. Will bookmark as suggested!

  2. John Hance

    Kudos on the great info, Erroll. Once again, your efforts are appreciated!

    Just adding my own two cents worth here, but Amy and I just last night finished the last bottle of my latest blueberry wine. That marks the third or fourth batch I’ve made, and I haven’t ever had a stuck fermentation. I also don’t use pectic enzyme. I did on the first batch, but used all my supply up since and just chose not to get any new for the next few batches. I didn’t notice any difference in quality or taste – or any other measurable criteria – with the ingredient missing. I therefor concluded that it simply isn’t necessary for my recipe and have dropped it altogether. I do ferment on the fruit like a red, and I only freeze-thaw if I have berries already frozen; this last batch were slightly-over-ripe, “fresh” berries which the grocery store was about to toss. The others were all bought frozen. I did, however, notice a difference in the body of this last batch. It seemed slightly “thinner” in the mouth. I don’t know how much of that to attribute to the fruit itself and how much to attribute to the fact that I deliberately lowered the alcohol to 12%. As you may recall, I’m striving to make my wines with a much more “normal” alcohol content range. Previous batches were in the 15-17% range; this was the first one at 12%. All in all, a very respectable wine!

    Thanks again, Erroll. Keep doing what you’ve been doing. I read every word over and over again, as always!

  3. Erroll Post author

    It’s good to hear from you John,

    Winemakers use pectic enzyme to increase juice yield and to clarify their wine. As a clarifier, it’s more important in white wines – how different would a red wine with a pectin haze look from a red wine without a pectin haze? I don’t think I would notice. Then there’s juice yield. I usually don’t measure this, and I doubt many home wine makers do either. So it’s possible to get a benefit without noticing it. As with clarifying, this effect is probably more important in white wines than red because fermenting on the fruit will do a lot to free up juice.

    All things equal, lower alcohol wines will have less body than higher alcohol wines, so I think you’re right about that. One thing about alcohol levels in red wine: do everything you can to get a clear sample because suspended solids from crushed fruit can make your hydrometer read high. You can do things like let it settle in the refrigerator overnight, filtering with paper towels then coffee filters (this is tedious and requires changing the “filter” but it does work).

    Congratulations on your blueberry wine!

    Erroll

  4. rajendra

    sir can u please tell me the name of the compound which is responsible for the colour in blueberries?

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