Hedley

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Hi all,

I have just started using the hydrometer and think I understand it.

However, in another thread someone mentioned that I should always top up my demijohn after racking so that it is nearly full (to stop oxidisation). That is all well and good, but I am now confused how this will affect the hydrometer reading.

I usually end up with about four and a half bottle's worth of wine at the end of the process. So I lose a bottle and a half through racking.

Is there a bit of maths I could do to adjust the SG reading depending on how much I have to top up with water? For example, say after the first racking I have lost half a bottle's worth. I add same amount of water to top up. Now I take an SG reading. Can I apply some formula to that to get an accurate reading based on the volume of wine I have effectively replaced with water?

Any help most appreciated.

Ross

Yooper

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Why not top up with wine? That's what most people do. Either a homemade wine, or a similar commercial wine.

If you're losing 25% of your wine, maybe you aren't racking efficiently. You want to rack off of the lees, but you don't need to leave so much wine behind.

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Hedley

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I have been using one of those devices you attach to the siphon tube. It leaves an inch of liquid behind, which is always too much. Maybe I can get one that is not so deep, or go back to just using the tube.

I like the idea of my wine being 100 per cent home made. I guess I could keep some homemade wine back to top up my demijohns...

oogaboogachiefwalkingdeer

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When you get close to the bottom tilt the carboy to make a pool on one side. If tilted slowly you won't disturb too much of the lees and can get all but a cup or so transferred to the new carboy. Mike

Hedley

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Thanks people! Good tips.

Does this topping up business mean you can only take an SG reading at the start of the process, and then at first racking? As once you top up that will throw any meaningful future SG reading out won't it?

Thanks for your help and patience with me on getting my head around this.

TedLarsen

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To my way of thinking, at least, the only really meaningful readings of specific gravity are the original gravity; the readings you take to ensure that fermentation is complete (by getting the same reading 3 or so days in a row); and the final gravity.

Oh, and if you backsweeten the wine (after stabilization), some people like to sweeten it to a particular S.G. to make sure it is exactly as sweet as they'd like.

Especially if you top off with the same (or similar) wine, I don't know what you'd learn by taking readings when you rack.

Hedley

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Maybe I'm not explaining well (sorry people!).

Say I have just transfered a gallon's worth of wine from primary fermentation to a demijohn, and I have taken an SG reading and noted it. After about a month I rack, and then top up with water. If I were to take an SG reading now, or at any point in he future, the 'drop' in SG will be bigger than if I had not added water (as I have diluted the original mix). To my understanding, adding water changes the liquid/sugar ratio and stops you from accurately determining the drop (the amount of sugar converted into alcohol). No?

novalou

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You can still estimate the percentage. Lets say you start off with a liter of juice and you measure potential alcohol at 12%. So you final volume will be 12% alcohol. Along the way you add 100mL of water. If you divide 12mL of alcohol(12%) by 1.1L, you get 9% alcohol.

Keep track of your volumes, how much water you add and you can estimate you final alcohol content.

Hedley

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Thanks Novalou,

That is useful. I knew there had to be a simple piece of maths I could apply to work out the volume of alcohol after adding water. However, this could only be used if you knew for certain the volume of alcohol before adding water, and part of the problem I am trying to get across here is how to determine that, using a hydrometer, whilst topping up before the process has finished/all the sugar converted.

My understanding of a hydrometer is that it measures the density of a liquid. In our case it effectively measures the sugar to water ratio. We take an SG reading at the start of the process, and then at the end, and we use the two different figures to calculate the 'drop', that is, how much 'less dense' the liquid has become; how much sugar has been converted. But if we add water at any stage inbetween the two readings, we invalidate the calculation.

If I take a starting SG reading of 1.090. Simply by adding water I could achive an SG reading of 1.000, as adding water will make the liquid less dense, and falsely indicate that sugar had been converted (when in fact the sugar had merely been dispersed in the increased volume of water).

Let us say two identical batches of wine are on the go in laboratory conditions. Both have starting SG of 1.090. One is topped up throughout the process, and one is not. The SG of the one that gets topped up would drop faster, and this drop could be misconstrued as sugar conversion, no?

Does this make sense? Am I massively over looking or over thinking something here?

Sorry to keep pushing but I think others would also benefit from learning about this. I really appreciate all the replies so far. You have all been really helpful this last year and hopefully I will be able to help and contribute advice to this forum one day!

All the best,

Ross

novalou

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As long as you know your initial Gravity reading, the amount of alcohol per will not change for the life of the batch, as long as you ferment dry.

As it is fermenting, gravity readings along the way tell you progress.

Back to my original example, 12% based on original gravity reading will remain constant in relation to your volume. So if you loose some volume, multiply you new volume by 12% to get the new volume of alcohol. It's that simple.

Don't be worried about SG readings during fermentation, it just tells you where the yeast is at!