Hydrometer readings with whole fruit

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Nick Z

Well-Known Member
Nov 23, 2019
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I am thinking about making my first batch of wine. I have a bunch of blueberries frozen that I can thaw out and use. I just got a two gallon fermenting bucket. I was figuring I would find a recipe I liked and fill that bucket. I will probably try to put the thawed blueberries into a paint strainer so that I can remove them more easily later when I rack the wine to a gallon glass jug.

And my hydrometer just came. I've never used one before but the instructions seem fairly straightforward. At least they seem straightforward when I am dealing with just liquid.

But if there is whole fruit in the bucket I won't be able to get a pure liquid, right? Yeah, I can mash the blueberries some but I would think the liquid portion I snag for a reading still won't take the whole fruit into account. I may not be explaining this well. But I am concerned I won't get an accurate reading. I figure once I've siphoned off the liquid portion into the secondary it won't be as big an issue. But if the initial reading is inaccurate won't that throw everything off?

Also, when using whole fruit can I still use campden tablets to knock out wild bugs? These are raw blueberries and I'm not willing to heat pasteurize them or cook them. But I don't know if campden only works on pure liquids.

I apologize for such basic questions. I did search through the forums first and couldn't find answers to these questions.

It's tempting to just try juicing the blueberries with cheesecloth but I was told to use the whole berries for more blueberry flavor. But I have never dealt with anything except apple juice up until now. And I would like to learn how to use whole fruit or fruit purees and this seems like as good a way to start as any.
Yeah you need about 1-2oz of liquid to use a hydrometer. Try to get juice as pulp free as possible.

  • Make sure the hydrometer is free floating in the cylinder.
  • Give it a spin to release any bubbles or particles clinging to it.
  • Make sure the liquid and hydrometer are at the calibration temperature.
  • Read the bottom of the meniscus.
  • Be careful, they are fragile.

The solid portion of the fruit doesn't matter because the sugar is all dissolved.

Sulfite does adequately work on mashed fruit/puree.

You may find yourself wanting a refractometer for situations like this since you need only a few drops of juice to get an original gravity reading. They're about $18-25 on Amazon for low end price range models, which seem to be adequate. However refractometers are a little more finicky and are no longer accurate once alcohol is present.

For most fruit wine people add water and sugar, which accomplishes two things:
It lowers the acidity.
It raises the ABV.

Either way I would mash the blueberries while containing then in a mesh bag. This will make separating the solids from the wine a lot easier later.
Even if I mash the berries, put them in a bag, and stick that bag in the fermenter (with the water and sugar added) won't there still be juice and sugar "locked up" in the berries?

I guess what I'm saying is that if the mixture isn't homogenous how can I get a proper gravity reading?
Imagine you cut an orange in half and juice one half to measure the gravity, could you assume the other half is the same?
^ yes, within reason.

However once you start diluting it with water and adding sugar, things get more complicated.
You need to measure the s.g. of the juice and then attempt to measure the volume of fruit juice being added, which you can base on weight but then subtract the presumed volume of solids.
Then you measure or calculate the gravity and volume of the sugar water.
Finally you use a blending calculation to determine the combined gravity and volume.
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I’ve been letting the mashed berries soak in peptic enzyme for 12-24 hours before adding the water. If your fruit isn’t in a bag, get a fine kitchen strainer, dip that into the must like a basket, and pretty much just juice will fill the strainer for you to draw your test from.
I add as much sugar as I would need for the entire volume of the must including the fruit. If you Squeeze the bag or press your fruit when you pull it, you’ll see you really have almost as much volume as you started with. You’ll lose the volume come racking off the lees though.
Can I use a paint strainer bag from Home Depot? When I looked at the strainer bags at the brew shop they looked exactly like nylon paint strainers. I suspect they just cut those up and resold them.

I would assume I need to boil the bag or soak it in sanitizer prior to use?
I’ve read many people use them, then almost as many say don’t because they’re not food grade.
I'm one that does use the paint strainers. I soak them in starsan for a couple minutes before use and use a ziptie to keep closed. It does make it easy to remove the fruit after a week or so. After dumping the used fruit in my compost pile, I rinse out the used bag, then soak it for a couple days in an oxyclean solution.
I'm going to use the paint strainers as well. Less expensive and easier to get. Also, I'm pretty what the brew shop was selling was paint strainers from Home Depot. I've spoken to the owner a couple of times and he clearly knows what he's doing so I trust that these are fine.

I'm not even totally convinced there is a different between "food grade" plastic and any other plastic. I suspect they all come off the assembly line with the same chemistry and some get labeled food grade and sold at a higher price.

It may be like "food safe" wood finishes. All wood film forming wood finishes are food safe once cured. They all cure into some version of plastic (with the exception of shellac, which is actually edible) and they all use similar chemistries and the same metallic salts as driers. And even if for some reason you sanded off the finish and ate it the actual amount of material is so infinitesimal it wouldn't do you any harm.
I'm not even totally convinced there is a different between "food grade" plastic and any other plastic.
Food grade shouldn't have BPA or DEHP, unlike many/most other plastics. There's also typically less dye.
Food grade shouldn't have BPA or DEHP, unlike many/most other plastics. There's also typically less dye.

I was under the impression that BPA was being phased out of most plastics? I'm not an authority on the subject, just to be clear.
I believe that’s only in bottles and food containers, so if it’s not good grade...
So, I just pitched the yeast for two gallons of blueberry wine. I basically followed a recipe I saw online and scaled it down. I just took an initial gravity reading and the potential alcohol is about 9%. Is that too low? I was under the impression wine was supposed to be above 12%? I can probably toss in another cup of sugar without overflowing the fermenter. Maybe two.