Why does anyone use a hydrometer?

[ScottM]

Attenuation is only really valid when there is a mix of sugars, ie complex through to simple, as the attenuation is based on how far down the road to complex the yeast will go. When a brew is 100% simple sugar, the yeast will convert all the sugar.

That's why I was asking. I want to know whether that is really true.

Very simple to know that's true, look at wine. Final gravity goes lower the more sugar you put in it, if that wasn't the case the final gravity would increase with more sugar.

 

[rpt]

I'll explain why I'm asking this. Wort contains a number of different types of sugar, all of which add to the original gravity but not all of which are fermentable. You can do a forced ferment test which will convert all fermentable sugars. But in a normal beer fermentation not all sugars get converted for various reasons:

Home Brew Talk[/url]]Though yeast strains are able to ferment all the sugars in the beer, they usually don't get to. In contrast to a forced ferment test, beer is generally fermented at lower temperatures, with smaller pitching rates and without constant rousing. Because of that the yeast will not get a chance to ferment all fermentable sugars in the wort. Flocculation will cause it to drop to the bottom or collect on the surface where it doesn't have as much contact with the sugars anymore. Because of nutrient depletion and or high alcohol levels cells die before they get a chance to ferment every last bit of sugar in the wort. The result is left over fermentable sugars that play an important role in the character of the finished beer. The closer a beer's attenuation is to its limit the drier and less sweet it will taste. When looking at the attenuation ranges given for commercial yeast you will notice that the less flocculating a yeast is, the more attenuative it will be. This makes sense as the poorly flocculating yeasts will remain in contact with the wort for a longer time.

So I'm wondering whether when you add dextrose or sucrose to wort you can be sure that 100% will be fermented or whether that is going to be subject to the same restrictions as the other sugars.

 

[ScottM]

I doubt it will be 100% for the reasons stated but it'll definitely be thereabouts, and higher than what the attenuation would be in a beer.

It would be an interesting experiment to try an ale yeast in water/nutrient/sugar against a turbo yeast in water/nutrient/sugar. Regardless of the results, the apparent attenuation would be over 100% as they would both finish way below 1.000.


Here's what I would make of it...

1L water
100g sugar

Attenuation 75%
OG 1.036
Predicted FG 0.997
Predicted Apparent attenuation 108%

Attenuation 80%
OG 1.036
Predicted FG 0.994
Predicted Apparent attenuation 117%

My calculations always make assumptions though, and one of those assumptions is that not all of the brew is fermentable. With that in mind I believe these 2 yeasts would be closer than my calculations predict. Would be an interesting experiment to try out though.


Edit:

Just been thinking about this a little further. If all sugar was converted to alcohol and none was converted to esters etc then I believe the theoretical maximum alcohol for 100g of sugar is 61ml. 61ml in 1L is 6.1% which would require an FG of 0.990. I doubt this would ever be atainable due to the esters etc, so just above that would probably be the theoretical maximum... maybe 0.991/0.992?

 

[scheelings]

Just been thinking about this a little further. If all sugar was converted to alcohol and none was converted to esters etc then I believe the theoretical maximum alcohol for 100g of sugar is 61ml. 61ml in 1L is 6.1% which would require an FG of 0.990. I doubt this would ever be atainable due to the esters etc, so just above that would probably be the theoretical maximum... maybe 0.991/0.992?

Hi Scott, can you please explain your calculation of 61ml? I ended up with a different result:

Every 100g of sugar, yields 53.8g of ethanol

The density of ethanol is 0.789 g/cm³
1L ethanol = 0.789*1 => 0.789KG

Therefore 53.8g of ethanol = 68.23 millilitres of ethanol

 

[ScottM]

Just been thinking about this a little further. If all sugar was converted to alcohol and none was converted to esters etc then I believe the theoretical maximum alcohol for 100g of sugar is 61ml. 61ml in 1L is 6.1% which would require an FG of 0.990. I doubt this would ever be atainable due to the esters etc, so just above that would probably be the theoretical maximum... maybe 0.991/0.992?

Hi Scott, can you please explain your calculation of 61ml? I ended up with a different result:

Every 100g of sugar, yields 53.8g of ethanol

The density of ethanol is 0.789 g/cm³
1L ethanol = 0.789*1 => 0.789KG

Therefore 53.8g of ethanol = 68.23 millilitres of ethanol

I'm quoting, but I don't want to link as it may be breaking forum rules. Here is the paraphrase of where I got 61ml from...

The theoretical yield is 51.1%, but you will get less than this, around 48% because you lose some of the sugars to forming the small amounts of other alcohols, esters, etc (eg 480 g (610 mL) of ethanol for every 1 kg sugar).

 

[jarenault]

You should be able to work out the attenuation based on your OG and FG.

Did you keep a hold of the recordings?

Can't find them. Tell you what though, I'll repeat the experiment starting tomorrow because it's shaping up to be a slow day.

 

[ScottM]

Excellent.

If you can, would you weigh the water and sugar as well :)

 

[jarenault]

Excellent.

If you can, would you weigh the water and sugar as well :)

No probs. We have scales accurate to a milligram at work. The kind that you have to operate within an enclosed glass case.
To be accurate you have to blast the subject with air before weighing and reweighing because even dust can corrupt your results.
The only yeast we have is generic "fermentative yeast", though.

We have to assume no mass lost from the vessel, bung or airlock (itself) over the fermentation period though.

 

[ScottM]

Ideal, I wouldn't worry too much with the yeast. It would be nice to compare a few though but even just one run at it should provide good info :)

 

[jarenault]

Ideal, I wouldn't worry too much with the yeast. It would be nice to compare a few though but even just one run at it should provide good info :)

I've often wondered if I could "evolve" a super tolerant yeast over a couple of years, just starting with the generic crap we have in the lab.
The good thing about my job is that if I'm producing the results in my "real" work, nobody bothers too much if I'm messing about in my downtime. In fact, it's sort of passively encouraged (as long as the messing about involves some kind of science).

 

[ScottM]

Any jobs going? Your work would LOVE me :ugeek:

Mine..... not so much lol

 

[jarenault]

Any jobs going? Your work would LOVE me :ugeek:

Mine..... not so much lol

It's an academic research lab so free-thought and "playing" is encouraged to an extent. The caveat is that if you actually stumble on anything interesting the uni owns the intellectual property.