Topping up and the hydrometer

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Hedley

Well-Known Member
Joined
Nov 6, 2011
Messages
126
Reaction score
4
Location
Bristol
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
 
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.
 
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...
 
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
 
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.
 
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.
 
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?
 
Hedley said:
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?

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.
 
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
 
Hedley said:
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

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!
 
Thanks. Ah I think I see.

So if I start with a reading of say 1.090, giving me a potential 12 per cent alcohol volume in the gallon, as long as I maintain that volume, by topping up with water to account for loses during racking, it shoud end up at 12 per cent still?

As I have NOT been topping up during my wine making so far, does that mean that my finished wines, being less than a gallon by a bottle or two, have actually been higher in alcohol than my starting potential?
 
Still, though, please don't miss the larger point: regardless of ABV, why would you water down your wine? Topping off with water is going to give you watered down wine, literally.

Most -- if not virtually all -- winemakers here top off their wines, and I daresay virtually of all of them top off with wine. Either top off with a commercial wine that is very similar to the wine you've made, or size the batch so that you have an extra half gallon or so that you ferment in a second carboy/bottle, and use that extra for topping off.
 
What about if I took an SG reading at racking, and then made up a water/sugar mix to match that SG, which I used to top up? Would that keep everything constant, the sugar converting into alcohol?
 
TedLarsen said:
Still, though, please don't miss the larger point: regardless of ABV, why would you water down your wine? Topping off with water is going to give you watered down wine, literally.

Most -- if not virtually all -- winemakers here top off their wines, and I daresay virtually of all of them top off with wine. Either top off with a commercial wine that is very similar to the wine you've made, or size the batch so that you have an extra half gallon or so that you ferment in a second carboy/bottle, and use that extra for topping off.

Yes, I agree. Top off with wine, juice with same SG, or rack into a smaller container.

If you do top up with water, it will lower you ABV.
 
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

So, I had to delve into my chemistry roots to get this formula, but so long as you use the same unit of measure throughout the whole thing, it works like a charm!

To start off, you need to measure 4 things:
1. The Specific Gravity of what you already have in your fermentor, we'll call it G1
2. The Volume of what you already have in your fermentor, V1
3. The Specific Gravity of what you are topping off with, G2
4. The Volume of what you are topping off with, V2

What ever you measure your volume with (gallons, liters, quarts, etc.) needs to be the same for both your V1 and V2 for this to work. You can't say your V1 is 3 gallons and your V2 is 1 quart. You would instead use 3 gallons and 0.25 gallons. Same goes for metric volume.

So here is the magic formula, keeping in mind that * is multiply and / is divide and anything in () you do first before going on to the next portion!

:eek:nestar:Final Gravity= ((G1*V1)+(G2*V2))/(V1+V2) :pipe:

Might be confusing :confused: but let's try an example before you give up! :eek:

Say you have a must that, after you rack, is only 4 gallons. It's in a 5 gallon carboy, so naturally you need to top up with 1 more gallon. The S.G of your 4 gallon must is 1.07, and you're topping up with 1 gallon of 1.02 must from a previous batch.

Your measurements would then be:
G1= 1.07 and V1= 4
G2= 1.02 and V2= 1

Now plug it all in!

FG= ((1.07*4)+(1.02*1))/(4+1)

Then we start simplifying: Multiply 1.07 and 4, then 1.02 and 1

FG= (4.28+1.02)/(4+1)

Do it again: 4.28 plus 1.02, then 4 plus 1

FG= 5.30/5

Finish it off by dividing 5.30 by 5 and....

Your Final Gravity= 1.06! :mug:

I love this formula because even if you don't use water to top up, it still works! I like making cysers (love child of mead and cider) so I always top up with more apple juice, which does not have the same specific gravity as water (which is 1.000).

If anybody needs anymore clarification, or just wants help with their particular batch they are topping up, feel free to drop me a message! ;)
 
One thing you might do that would remove all the issues of dilution or concentration (and so the need to use the Pearson's Square (see PersephonesHell post , above) would be to begin fermenting in a bucket and if you are planning on making 5 L of wine start with 6 or 7 liters all at the starting gravity you are aiming for (say 1.090). When you rack the first time you will rack into your 5 gallon carboy - and that will be full and the liter or liter and a half you have left over after racking you should rack into wine bottles and store these in your fridge. The cold will prevent them from actively fermenting. The next time you rack and lose an inch or two of wine you top up from the bottles you have had stored in your fridge. As that topping up wine reaches the ambient temperature of your fermenting room it will then start to ferment so the length of the fermentation of your wine will increase BUT you are neither diluting your wine nor adding anything "artificial" or anything you have not yourself made.
 
Don't confuse SG with the ability to make alcohol. Every liquid has a Specific Gravity, and it is compared to pure water (which is 1.000). We assume that anything over 1.000 is sugar, just to make it easier to figure.

So, lets say that you have very hard water and its SG is 1.04, now what do you do?

I say don't worry about it. Keep the starting SG around 1.092 to 1.100 and let it ferment and you will end up with wine. Who cares if it is 14.1% or 13.5%, as long as it is over 11% it will be just fine.
 
Back
Top