Fermentation Speed Unit
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Claude Jolicoeur
Jun 8, 2012, 10:36:26 AM6/8/12
to Cider Workshop
On another thread, we discussed fermentation speed in so many
different ways:
- Number of days for a drop of 1 point of density
- Drop of SG per day, or of points of density per day
- Drop per month
And so on... This may become confusing so I thought of a way to
express the speed of fermentation that would be simple and uniform.
I suggest to call this unit FSU (for Fermentation Speed Unit), and 1
FSU would be defined as the speed of fermentation that would cause a
reduction of the density by 1 point in 100 days (or a SG drop of 0.001
in 100 days).
With this unit, we would have:
1 FSU a very slow fermentation, i.e. stable for any practical
purposes.
10 FSU a slow fermentation where the density drops by one point in 10
days
100 FSU a fast fermentation where the density drops by one point per
day.
And the bottling recommendations I have written in a few occasions in
this forum would then become:
Less than 3 FSU, very safe, the cider might develop a slight fizz
after 3-4 months in bottle.
Between 3 and 5 FSU, safe, the cider will most likely become slightly
petillant.
Between 5 and 10 FSU, more risky, the cider is more likely to become
fully sparkling after a while in bottles, and you could be in a
position where you will have to drink all the remaining cider in a
short time span.
In all cases, when bottling a cider at a SG higher than 1.010, a test
bottle strategy should be followed:
The test bottle(s) should be kept at room temperature (assuming that
the bulk is kept in a cold room).
After approximately 2 months, first bottle should be checked and SG
measured. Speed of fermentation should be evaluated since bottling.
Other test bottles may be used after 4 and 6 months depending on the
needs and the evolution of the cider.
Another important point, when bottling cider at a high SG, always use
full weight Champagne bottles even if the FSU is low.
Evaluation of the FSU from 2 SG readings:
Assuming SG1 measured at day 0
After N days another SG reading is taken, that we call SG2
Express the difference SG2 - SG1 in points of density
Divide by N the number of days and multiply by 100
Example, SG1 = 1.016
SG2 = 1.014, taken 33 days later
SG2 - SG1 gives 2 points of density
then 100 * 2 / 33 gives 6 FSU
A note on the accuracy of this. Assuming a precision hydrometer is
used and temperature compensation is done, the SG may be evaluated to
an accuracy of approximately +/-0.0005. This means that if a value of,
say, 1.016 is read, it means that the real SG may be anywhere between
1.0165 and 1.0155. Similarely, with a reading of 1.014, the true SG
may be 1.0145 or 1.0135. Let's put this in our previous example:
The highest speed would be when SG1 is max and SG2 min, we would then
obtain 9 FSU.
And the slowest speed with SG1 at min and SG2 at max gives 3 FSU.
Hence, with our example, even with a good precision hydrometer, we
would be unsure as the true speed may be anywhere between 3 and 9 FSU.
Note that the accuracy improves greatly as the number of days between
the 2 measurements increases - this is why I was telling Erik in the
other thread that I thought 17 days was a short period of time between
the 2 measures of SG: with SG1 = SG2 = 1.017, N = 17 and an accuracy
of +/-0.0005 on SG, we may still have
SG1 = 1.0175, SG2 = 1.0165, which gives 6 FSU.
Any comments would be welcome on this FSU unit to express the speed of
fermentation...
Claude
different ways:
- Number of days for a drop of 1 point of density
- Drop of SG per day, or of points of density per day
- Drop per month
And so on... This may become confusing so I thought of a way to
express the speed of fermentation that would be simple and uniform.
I suggest to call this unit FSU (for Fermentation Speed Unit), and 1
FSU would be defined as the speed of fermentation that would cause a
reduction of the density by 1 point in 100 days (or a SG drop of 0.001
in 100 days).
With this unit, we would have:
1 FSU a very slow fermentation, i.e. stable for any practical
purposes.
10 FSU a slow fermentation where the density drops by one point in 10
days
100 FSU a fast fermentation where the density drops by one point per
day.
And the bottling recommendations I have written in a few occasions in
this forum would then become:
Less than 3 FSU, very safe, the cider might develop a slight fizz
after 3-4 months in bottle.
Between 3 and 5 FSU, safe, the cider will most likely become slightly
petillant.
Between 5 and 10 FSU, more risky, the cider is more likely to become
fully sparkling after a while in bottles, and you could be in a
position where you will have to drink all the remaining cider in a
short time span.
In all cases, when bottling a cider at a SG higher than 1.010, a test
bottle strategy should be followed:
The test bottle(s) should be kept at room temperature (assuming that
the bulk is kept in a cold room).
After approximately 2 months, first bottle should be checked and SG
measured. Speed of fermentation should be evaluated since bottling.
Other test bottles may be used after 4 and 6 months depending on the
needs and the evolution of the cider.
Another important point, when bottling cider at a high SG, always use
full weight Champagne bottles even if the FSU is low.
Evaluation of the FSU from 2 SG readings:
Assuming SG1 measured at day 0
After N days another SG reading is taken, that we call SG2
Express the difference SG2 - SG1 in points of density
Divide by N the number of days and multiply by 100
Example, SG1 = 1.016
SG2 = 1.014, taken 33 days later
SG2 - SG1 gives 2 points of density
then 100 * 2 / 33 gives 6 FSU
A note on the accuracy of this. Assuming a precision hydrometer is
used and temperature compensation is done, the SG may be evaluated to
an accuracy of approximately +/-0.0005. This means that if a value of,
say, 1.016 is read, it means that the real SG may be anywhere between
1.0165 and 1.0155. Similarely, with a reading of 1.014, the true SG
may be 1.0145 or 1.0135. Let's put this in our previous example:
The highest speed would be when SG1 is max and SG2 min, we would then
obtain 9 FSU.
And the slowest speed with SG1 at min and SG2 at max gives 3 FSU.
Hence, with our example, even with a good precision hydrometer, we
would be unsure as the true speed may be anywhere between 3 and 9 FSU.
Note that the accuracy improves greatly as the number of days between
the 2 measurements increases - this is why I was telling Erik in the
other thread that I thought 17 days was a short period of time between
the 2 measures of SG: with SG1 = SG2 = 1.017, N = 17 and an accuracy
of +/-0.0005 on SG, we may still have
SG1 = 1.0175, SG2 = 1.0165, which gives 6 FSU.
Any comments would be welcome on this FSU unit to express the speed of
fermentation...
Claude
Dries Muylaert
Jun 8, 2012, 1:14:37 PM6/8/12
to cider-w...@googlegroups.com
Dear Claude,
- should be expressed in function of fermentation temperature at the moment of taking the sample, I think. Fermenting liquid temperature will to a great extend influence fermentation speed.
- I am not a great believer in a hydrometer for measuring density of a fermenting sample. I use a refractometer. Boil down the fermenting sample to 50%. Add distilled water to 100%. Measure sample with refractometer. It will give you a more accurate picture on how the sugar density is evolving.
2012/6/8 Claude Jolicoeur <cjol...@gmail.com>
Claude
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Claude Jolicoeur
Jun 8, 2012, 2:23:34 PM6/8/12
to Cider Workshop
Dries Muylaert wrote:
> - should be expressed in function of fermentation temperature at the moment
> of taking the sample, I think. Fermenting liquid temperature will to a
> great extend influence fermentation speed.
Dries, you are totally right about the temperature - I completely
> - should be expressed in function of fermentation temperature at the moment
> of taking the sample, I think. Fermenting liquid temperature will to a
> great extend influence fermentation speed.
forgot to mention this! For my part, I will usually start to look at
fermentation speed as spring arrives and T gets over 10C. Colder than
that, fermentation is too slow for the speed to be really
significative.
It may be worth mentioning here that Bauduin in "Guide pratique de la
fabrication du cidre" proposes the following correction in function of
the temperature:
speed at 10C = speed at T * (10C)/(TC)
i.e. if you measure a speed 4 FSU at T=5C, it would be equivalent to 8
FSU at 10C. I don't know however on what scientific grounds this
correction is based on.
> - I am not a great believer in a hydrometer for measuring density of a
> fermenting sample. I use a refractometer. Boil down the fermenting sample
> to 50%. Add distilled water to 100%. Measure sample with refractometer. It
> will give you a more accurate picture on how the sugar density is evolving.
thus making the refractometer reading more accurate. I have a few
questions...
What size of sample do you use?
How long does it take you to make a measurement?
Can you discriminate a difference of 0.1 Brix with your refractometer?
You would then express the speed as loss of sugar (in g per 100g or in
grams per liter) per unit of time.
Claude
Dries Muylaert
Jun 8, 2012, 2:53:59 PM6/8/12
to cider-w...@googlegroups.com
By boiling you do not only eliminate the alcohol, but also the carbon dioxide and the yeast in suspension. The latter if you set the sample to rest for a day in the fridge. Will form a sediment. For the refracto you need only a droplet. For boiling down I use 200 cc, reducing it to 100, adding 100 cc of distilled water. It does not give an exact measurement, for that you need lab conditions, but it gives you a pretty good idea of the density. That density is of course not only caused by sugars, as you know. Main issue is that the alcohol, carbon dioxide and the yeast in suspension can no longer interfere in the results.
Oe: 0-170, point by point indicated on the refracto scale.
have a nice weekend
2012/6/8 Claude Jolicoeur <cjol...@gmail.com>
Claude
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