Adding sugar during aerobic fermetation

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Sep 7, 2009
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Hi - newbie question, be gentle! Here's the history:

Yesterday - picked 14lb plums of the tree, washed in cold water, halved, destoned and put in bucket. Poured on about 2 gallon boiling water (8 kettles full). Left overnight with loose fitting lid.

Today: tested SG 1.2. Added 2kg sugar new SG 1.7. Added cup of cold tea too. Added yeast and put the lid back on.

Tonight: been reading the posts here and think I should have added more sugar to get SG 1.9...

Too late to get more sugar now will get some more tomorrow, another 1kg bag should do it but is there likely to be any problem adding sugar once the fermentation is underway? Or should I add it when moving the must into airlocked demijohns (which again having read the posts here I'm planning to do when the SG returns to about 1.2).

Meanwhile the must seems be be bubbling away quite nicely.

Many thanks
Hello Mike and welcome to the forum.

well if you wanted to up the abv you can check the wine with a hydrometer and adjust the sugar levels by the difference between what has already fermented out and what you actually wanted to begin with.

for example it started at 1.070 .. you wanted 1.090 the differnce is .020

so take the SG now.. for example if it is now 1.052.. you'd need to add enough sugar to bring it up to 1.072 to approximate the same level that you wanted to start with.

I know Luc has a table of how much sugar you add per gallon to achieve the correct abv.. I usually just fiddle and test til I get it where I want it to be.

Definitely raise it up to around 1.085 and welcome. Did you add any yeast nutrient or pectic enzyme? pectic enzyme is what will help break down the fruit and extracct flavor and color for your wine.

Welcome to our great hobby. A couplke of comments on your post.

1. Please quote specific gravity as 3 decimal places. In this case, we can be pretty sure that 1.7 actually means 1.070, but in other situations 1.7 might mean 1.070 or 1.007 (and those readings can give widely different responses to most questions).

2. Assuming a 1.070 start and a .995 finish, you will get a 10% (roughly) wine. That would be great for many fruit wine makers. You do not have to boost the sugar. I am not much of a fruit wine maker, but I would be happy with 1.070.

Measuring sugar levels in these fruit wines has me wondering about something. Even measuring with a hydrometer at the beginning isn't there still a lot of unreleased sugar in the fruit itself ? Just makes me wonder how accurate a gravity reading can be ?
If you did a good job of squeezing the fruit then there shouldnt be that much undissolved sugars left, it wont make much difference. Mike, all I saw was 1.2 and I was guessing that meant 1.020 cause hydrometers dont go as high as 1.2 and didnt even notice you did bring it up to 1.070. 1.070 is a tad low but acceptable, I personally would bring it up that little bit higher especially if you plan on aging this wine beyond 1 1/2 years.
I don't see any acid adjustments.

I make my plum wine from pure plum juice.
My acid levels are at a point that it is not needed to
dillute the juice that much as you did.

That way you also there is no need to add that much sugar.

Thanks for feedback everyone.

Today maybe 20 hours after adding yeast the SG is 1.060, nice gentle frothing, nice crust on the top I just pushed down. I was a bit worried the yeast was past its sell by but seems to be off to a good start.

I didn't add any pectin enzyme is it too late to add now I'll see if I can get some today when i get the additional sugar. I haven't yet learned how to measure acid levels either...

Thanks again
Adding pectic enzyme during an active fermentation
might not work as yeast might inhibit the enzymes.
I tested that in this story:

So you can do it (pectic enzymes do not do any harm).
You could also wait till fermentation is over and add the enzymes when the wine is aging. Maybe it clears on its own and then
you will not need to add them at all.

I have read in more than one book that pectic enzyme is not particularly effective in the presence of active yeast fermentation.. the yeast action inhibits it.

this is why most recipes follow a script of 24 hours between adding pectic enzyme and adding the yeast.

you can add it to the wine when it has finished fermenting and it will remove the pectic haze.


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