Measuring sugar consumption

[Spaceman]

Has anyone had any luck with measuring the amount of sugar digested by the scoby during fermentation? I've tried hygrometer readings but that has proven to be inaccurate.

Thanks!

 

[snarf]

Yes, I agree that hyDrometer readings are no good for kombucha. I'm not aware of any simple method to measure the sugar content of finished kombucha. My guess would be that about 50% of the original sugar is still in there. Of course this depends on how long you let your brew ferment...

 

[Spaceman]

I'm typically doing 14 days minimum and assuming 65% attenuation by the yeast. I do this to guarantee I'm not going over 0.5% alcohol.

I would love to know of a method that validates my recipe and assumptions.

 

[EPBREWER]

I was told by a commercial brewer that they use a BRIX meter to more or less tell how much sugar has been consumed by the culture. I found one on Amazon for about $25 and it has worked out great.

 

[ericbw]

I was told by a commercial brewer that they use a BRIX meter to more or less tell how much sugar has been consumed by the culture. I found one on Amazon for about $25 and it has worked out great.

What was your consumption?

 

[Spaceman]

I've found brix measurements to be unreliable due to all the other 'stuff' that is in kombucha. Is yours a light refractometer by chance?

 

[ericbw]

Why are hydrometer readings not good for kombucha?

Just this morning, I started a batch of sweet tea. I added the sugar and dissolved it, then took a gravity reading. It was 1.022-1.023. BY my calculations, it should have been more like 1.016-1.018. That's pretty close, but it did make me wonder if the tea without sugar would have given me a reading higher than 1.000.

I also wonder why trub and hop debris don't seem to have an effect on using a hydrometer to check OG with beer. Maybe because it's not truly dissolved? But that's a separate topic!

 

[Spaceman]

I also wonder why trub and hop debris don't seem to have an effect on using a hydrometer to check OG with beer. Maybe because it's not truly dissolved? But that's a separate topic!

I think the problem is all the extra stuff made as a result of the kombucha fermentation. I tried a few brix measurements during secondary fermentation and the readings did not change, yet the CO2 content was clearly increasing, so the sugar should have gone down. Any ideas whats going on here?

 

[mano]

... I tried a few brix measurements during secondary fermentation and the readings did not change, yet the CO2 content was clearly increasing, so the sugar should have gone down. Any ideas whats going on here?

Assuming your brix reading were correct, it could still make sense that sugar content remained constant while CO2 content increased. A case like that could be explained by the bacteria (and not the yeast) being responsible for creating more CO2 by consuming alcohol.

 

[mano]

Hi guys I am new to the forum and joined mainly because my deep interest in Kombucha making. Has anybody collected more data to share?
I'll make my next kombucha batch in a week time (approximately) here is the data I am planning to collect:

1- SG of the water I am using (there could be salts and minerals affecting the reading)
2- SG of the tea Without sugar.
3- SG of the tea With the sugar.
4- SG after mixing with starter solution.
5- SG after one week of fermentation (depending on time I might read more often)
6- SG when ready to bottle.

I just have a hydrometer but I believe this should help us in understanding better, right? Any other thing I should measure?

Cheers

 

[ericbw]

I think it might be helpful to measure ph along with gravity, as I am sure there is a connection between the two as booch ferments.

 

[mano]

That is a good point. I have a pH-meter as well. By the way it is known what to expect in pH changes during a healthy fermentation, check this out: https://www.kombuchakamp.com/ph-kombucha-alkaline-acid-balance

 

[ericbw]

Interesting. I think there is a way to pinpoint brix and ph for the ideal (or consistent) flavor.

 

[Spaceman]

Assuming your brix reading were correct, it could still make sense that sugar content remained constant while CO2 content increased. A case like that could be explained by the bacteria (and not the yeast) being responsible for creating more CO2 by consuming alcohol.

I had not heard of the bacteria creating CO2 during ethanol consumption, is this correct?

 

[ericbw]

I had not heard of the bacteria creating CO2 during ethanol consumption, is this correct?

I think you are correct that bacteria do not create gas when they eat ethanol. That's why you add sugar to carbonate, not alcohol.

 

[Spaceman]

I think you are correct that bacteria do not create gas when they eat ethanol. That's why you add sugar to carbonate, not alcohol.

Thanks for clarifying, I was having a moment of panic since my bottling process is built upon an assumed sugar attenuation % by the yeast.

The bacteria should only be producing acetic and amino acids from my understanding.

 

[ericbw]

But you know how you can get a beer infected, and it definitely eats more sugar than the regular yeast does - makes it sour. But I think we're correct that yeast (wild or unknown as well) make the gas.

 

[mano]

Hey guys you are right, the yeast is responsible for the CO2 production. During the aerobic fermentation happening in Kombucha, the ethanol is oxidised to acetic acid by the acetic acid bacteria. As you can see in this equation (C2H5OH + O2 --> CH3COOH + H2O), there is no CO2 formed besides the acid, just water . Sorry about this confusion.

 

[ericbw]

Hey guys you are right, the yeast is responsible for the CO2 production. During the aerobic fermentation happening in Kombucha, the ethanol is oxidised to acetic acid by the acetic acid bacteria. As you can see in this equation (C2H5OH + O2 --> CH3COOH + H2O), there is no CO2 formed besides the acid, just water . Sorry about this confusion.

Oh, the equation helps (not!)

 

[mano]

Hi I have already collected some data:

1- SG = 1.002, pH=7.3, T=20.0 oC (just tap water)
2- SG = 1.003, pH=6.3, T=23.9 oC (tea Without sugar)
3- SG = 1.036, pH=6.0, T=26.1 oC (tea With the sugar)
4- SG = 1.034, pH=3.8, T=25.0 oC (after mixing with starter solution)
5- SG = 1.034, pH=3.6, T=23.0 (5 days of fermentation)

The SG readings are already corrected by temperature. I might take a few more readings before bottling.

 

[Spaceman]

Hi I have already collected some data:

1- SG = 1.002, pH=7.3, T=20.0 oC (just tap water)
2- SG = 1.003, pH=6.3, T=23.9 oC (tea Without sugar)
3- SG = 1.036, pH=6.0, T=26.1 oC (tea With the sugar)
4- SG = 1.034, pH=3.8, T=25.0 oC (after mixing with starter solution)
5- SG = 1.034, pH=3.6, T=23.0 (5 days of fermentation)

The SG readings are already corrected by temperature. I might take a few more readings before bottling.

How exactly are the last 3 gravity readings useful? After a 5 day fermentation your gravity dropped by 0.002. What does this tell you?

Your pH after adding starter tea is 3.8? How much starter tea is that?

Very interesting data here!

 

[mano]

The first reading shows that the water I use has slightly higher density than pure water (it makes sense to me, and it is good to keep in mind for potential alcohol level correction). By looking at the second one it seems that the tea solution increases a bit more the density of the liquid (but this could also not be the case because the error in my hydrometer is actually +/- 0.001 ). The third reading shows the increase in density due to sugar addition. But since the starter solution has very low sugar content the resultant blend (sweet tea + starter) has an overall density smaller than just the sweet tea, so far it still makes sense, right?
The fourth reading will determine your alcohol content (assuming that not acetic acid is produced). What is interesting to me is that 5 days after fermentation started, the sugar levels seems to be same as in day 1, which is hard for me to believe because I observed some CO2 already. I look forward to collect more data and hopefully at the end all makes sense, or perhaps not

Cheers

 

[mano]

How exactly are the last 3 gravity readings useful? After a 5 day fermentation your gravity dropped by 0.002. What does this tell you?

Your pH after adding starter tea is 3.8? How much starter tea is that?

Very interesting data here!

Sweet tea --> 9 Litres
Starter solution --> 1 Litre

 

[Spaceman]

The first reading shows that the water I use has slightly higher density than pure water (it makes sense to me, and it is good to keep in mind for potential alcohol level correction). By looking at the second one it seems that the tea solution increases a bit more the density of the liquid (but this could also not be the case because the error in my hydrometer is actually +/- 0.001 ). The third reading shows the increase in density due to sugar addition. But since the starter solution has very low sugar content the resultant blend (sweet tea + starter) has an overall density smaller than just the sweet tea, so far it still makes sense, right?
The fourth reading will determine your alcohol content (assuming that not acetic acid is produced). What is interesting to me is that 5 days after fermentation started, the sugar levels seems to be same as in day 1, which is hard for me to believe because I observed some CO2 already. I look forward to collect more data and hopefully at the end all makes sense, or perhaps not

Cheers

Acetic acid is produced by the bacteria during the fermentation. To me it seems the hydrometer isn't accurate because it is suggesting that the sugar isn't being consumed by the yeast either with how little your numbers changed, but you saw CO2 bubbles so the yeast were likely active.

Your numbers all make sense to me. It's really just that 5th reading that seems off. Perhaps you only add a very small amount of sugar and that accounts for the 0.002 change?

You must have some very strong starter to get a pH of 3.8 after adding only 10%! My starting pH is usually between 6.1 and 6.5, but I only add about 6% starter tea.

 

[mano]

Hi,

The fermentation was active, which means sugar is being consumed. However the SG did not decrease from the fourth to the fifth reading because the produced acetic acid has larger density than water

Once more density (or specific gravity) measurement using our lovely hydrometer is not the right approach to track sugar consumption in Kombucha. It all makes sense to me now.

It is better explained here::
https://www.homebrewtalk.com/showthread.php?t=576365