Using a hydrometer to work out how much sugar to add to your wine. (Or not.)

We're often asked at this time of year for advice on making wine from garden grapes. And using a hydrometer.

Assuming your grapes are ripe and sweet, there should be a lot of sugar in your grape juice already. But English garden grapes (as opposed to, say, pinot noir grapes grown specifically because they make great wine) tend to be a bit acidic for winemaking. Even if they taste nice when you eat one.

There are two ways to work out how much sugar you need to add to your grape juice once extracted to ensure a good fermentation. Either using a hydrometer, or not. Whichever method you use, it is likely you'll need to add quite a lot of sugar to garden grape juice. So be prepared for that.

Using a hydrometer

You use a hydrometer to measure how much sugar is occurring naturally in your juice. Then simply add the appropriate amount of sugar to get the alcohol content you want. You'll find many tables online to help you decide how much sugar to add, and the likely resultant alcohol content of your final wine. Or you can use the one below.
Specific Gravity Sugar (grams per Sugar (oz per Potential alcohol %
At 20 degrees C Litre) Gallon) By volume
1.000 0 0 0
1.005 13 2 0.6
1.010 26 4 1.3
1.015 39 6 1.9
1.020 52 8 2.6
1.025 64 10 3.2
1.030 78 12 3.9
1.035 91 15 4.5
1.040 104 17 5.2
1.045 117 19 5.8
1.050 130 21 6.4
1.055 143 23 7.1
1.060 157 25 7.7
1.065 169 27 8.4
1.070 183 29 9.0
1.075 195 31 9.7
1.080 209 34 10.3
1.085 222 36 11.0
1.090 235 38 11.6
1.095 248 40 12.3
1.100 261 42 12.9
1.105 275 44 13.5
1.110 288 46 14.2
1.115 301 48 14.8
1.120 314 50 15.5
1.125 328 53 16.8
1.130 341 55 16.8
1.135 355 57 17.4
1.140 368 59 18.1
1.145 381 61 18.7
1.150 394 63 19.3

Do I have to use a hydrometer?

I read somewhere that making wine without a hydrometer is like driving at night without headlamps. You are wine making blindfolded, in a way. You could be adding too much sugar when the juice doesn't need it, or not enough when it does.

So the advice is: buy a hydrometer.

They're inexpensive (considerably less than £10, especially if the trial jar is plastic). And they're positively cheap when you consider that the alternative is risking all the juice you've lovingly extracted, and it all ending up down the sink. So we think a hydrometer is an investment worth making. And if you've bought a starter kit for making beer, wine or cider, the chances are it includes one anyway.

No hydrometer? You can still do this

But we would say that, wouldn't we. And meanwhile, I dare say, there are people all over the world happily making wine without one. So if you don't have a hydrometer and really want to get on with things right now, you can.

The general advice is: assume you will need to add UP TO 1 kilo of sugar for each 4.5 litres (ie per demijohn of grapejuice). So make sure you have that much sugar available in the house (household granulated sugar is fine), but please don't add it all at once.

Too much sugar can be just as problematic in winemaking as not adding enough. Instead, you will add it in parts. So add 250g per 4.5 litres of liquid at first, and check the next day to see if that creates a strong fermentation. If fermentation doesn't seem strong enough, add 100g more.

Keep adding a little every day until the fermentation is going well. If it won't get going at all, check that the space you have the vessel in is warm enough. Making wine from garden grapes often coincides with a sudden dip in temperatures, and cold weather slows down fermentation.

How to use a hydrometer

If you've recently bought one, it probably includes instructions on how to use a hydrometer. A hydrometer is one of those things that is really simple to use, but sounds terribly complicated when you attempt to explain it in a blog post. Then when you use one for the first time you think 'is that it?' So please bear that in mind as you read this explanation. It is more straightforward than I'm probably about to make it sound.

To use a hydrometer you need the hydrometer itself plus a trial jar. Most hydrometers come with a trial jar included. It's a long tube that is wider and longer than the hydrometer, you fill it with the liquid you wish to test and away you go.

Step one - clean the hydrometer and the trial jar

Clean and sterilise your hydrometer. As with all things home brew, if there are unwanted bugs in/on your equipment they can spoil your wine. So this bit is non-negotiable.

Don't be tempted to use boiling water as the hydrometer may not withstand the heat. Simply rinse the hydrometer and trial jar in warm water, then sterilise using a suitable sterilising solution. Rinse thoroughly.

This of course assumes that you wish to put the test liquid back into the must when you've finished. If you've got lots and intend to discard the test juice, then you won't need to sterilise.

Step two - draw off the juice

Put some juice from your must into the sterilised trial jar.

How to use a hydrometer

If you can't pour it, make sure whatever you do use is sterilised. A pipette, syphon tube, spoon, funnel...or in the case of this photograph, we were using a meat injector designed for marinades.

I know. Who has one of those? We do.

Put enough in so that, when you add the hydrometer to the liquid, it will float without overflowing. Put the hydrometer trial jar on the kitchen counter with the juice in it, gently lower the hydrometer into the liquid.

Step three - read the Specific Gravity (SG)

Spin the hydrometer stem (the thin end) between your thumb and forefinger before taking the reading so air bubbles don't interfere with it. When the hydrometer stops moving, take your reading at the point where the underside of the surface of the liquid meets the scale. Then put the juice back in the vessel, or discard it if you didn't sterilise the hydrometer and trial jar.

Step four - compare your reading with the chart

So now you know the SG of your juice/must, you know how much sugar you need to add.

Incidentally, hydrometers are also useful things when you come to the end of your fermentation. You'll want to be sure that fermentation has stopped before you start bottling, to avoid exploding bottles later on. If your wine is completely clear and you think fermentation has stopped but want to be certain, take a hydrometer reading of your wine 3 days in a row. If it stays the same, fermentation has stopped and you are safe to bottle.

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Other Off Grid Favourites:

Making Wine from Garden Grapes

Testing Yeast to see if it has Expired

Beginner's Guide to Making Cider from Apples

Image of how to use a Hydrometer


  • thank you, this was verry handy i was going to start my dry red wine with putting 4.5kilo of suger to 30 leters of juice and added water all at once, i didnt know that it had to go in in stages, plus know i know that your situated in great bar im going to pop in on the 7th to get some extra kit, to do the job properly, thanks for the advice and will see you shortly, karl.p

  • Hi Robin, I did indeed mean that, and I have corrected it. Thank you!

  • Hi, I found this very useful and interesting.
    However I think the old ‘cut, paste, edit’ bug has got in the brew.
    You have put, “Stand the hydrometer on the kitchen counter with the juice in it,” when I think what you mean is ‘put the trial jar on the kitchen counter’.
    If only there was an equivalent of Camden tablets to get rid of typing bugs! And ‘spoil chockers’ would be of no use, as all the words are correctly spelled.


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