SFDE during fermentation

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terryc...@gmail.com

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Oct 13, 2023, 3:33:20 AM10/13/23
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I make cider from apples in my small orchard. It is mostly naturally carbonated and semi-dry for home consumption etc. and I have been doing this happily for years.

However, I have a nagging question about the 2% - 3% non-fermentables in apple juice. The stuff that Claude Jolicoeur’s book calls SFDE (i.e. non-fermentable components like acids, tannin, etc).

If the SFDE remains untouched at the end of fermentation, it doesn’t appear to influence the final gravity at low SG. So, the question is…Is this because it does remain but has little effect on SG, does it have an effect that is conveniently offset by the alcohol which is at SG lower than 1.000, or is there some other reason?

My “engineering brain” would expect the SDFE to be left unchanged at the end of fermenting and so provide all the flavour characteristics. A juice with SG1.050 juice should have something like 20g/L of SFDE (although this may not have the same effect on SG as sugar). Without getting too hung up on the “sanctity of numbers” when trying to understand this, if I plot SFDE vs SG over a range of data that I have been able to gather, I find that there is a slope of around 0.47 g/L per gravity point, i.e. SFDE g/L isn’t the same over a range of SG as fermentation progresses, but I can’t think of a reason why.

Extrapolating the data back, I end up with something like zero SFDE at SG 1.000 rather than the 20g/L that was present at 1.050, suggesting that its influence on low SG is negligible. I am conscious that there will be variations between different tables because of different data sources.

The reason for asking the question is that when pasteurising for sweetness and carbonation, I use SG as a proxy for when to bottle for sweetness and carbonation. This might be a bit “clunky”, but it works for me. If I bottle at 1.010 then heat pasteurise at 2 volumes of C02 (monitored by a test bottle fitted with a pressure gauge) I expect the resulting SG to be around 1.006. Different tables tell me that at 1.006 the sugar could be anything from 11 to 16 grams per litre, which is about a 50% difference (the same applies at other levels of SG).

This isn’t a big deal, but it would be useful if anyone can enlighten me about whether some tables are based on sugar only or sugar plus SFDE, and also what happens to the SFDE as fermentation progresses.

Andrew Lea

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Oct 13, 2023, 8:53:42 AM10/13/23
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You might like to look over this paper from a Long Ashton report in 1960, which I posted here last year.  It should answer your questions about SFDE (sugar free dry extract).


As for SG tables, you are right that most are based (erroneously) on pure sugar solutions and a very few (mostly originating in France) are based on real-life data which allows for alcohol and SFDE.

Andrew

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Claude Jolicoeur

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Oct 13, 2023, 1:53:22 PM10/13/23
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See below some comments...

Le vendredi 13 octobre 2023 à 03:33:20 UTC-4, terryc...@gmail.com a écrit :

If the SFDE remains untouched at the end of fermentation, it doesn’t appear to influence the final gravity at low SG. So, the question is…Is this because it does remain but has little effect on SG, does it have an effect that is conveniently offset by the alcohol which is at SG lower than 1.000, or is there some other reason?

If you didn't have SDFE, dry finished cider would be at a SG around 1.090 (more or less depending on the alcohol) - hence if you read 1.000, this means the SDFE has rised the SG by about 10 points.
 

My “engineering brain” would expect the SDFE to be left unchanged at the end of fermenting and so provide all the flavour characteristics.

yes

A juice with SG1.050 juice should have something like 20g/L of SFDE (although this may not have the same effect on SG as sugar). Without getting too hung up on the “sanctity of numbers” when trying to understand this, if I plot SFDE vs SG over a range of data that I have been able to gather, I find that there is a slope of around 0.47 g/L per gravity point, i.e. SFDE g/L isn’t the same over a range of SG as fermentation progresses, but I can’t think of a reason why.

Actually, SFDE would remain fairly constant as fermentation progresses. It varies with the INITIAL SG - hence I presume the slope  you find relates the initial SG with the SDFE

Extrapolating the data back, I end up with something like zero SFDE at SG 1.000 rather than the 20g/L that was present at 1.050, suggesting that its influence on low SG is negligible. I am conscious that there will be variations between different tables because of different data sources.

This doesn't work... as SDFE won't decrease as fermentation progresses. It would be OK for a juice that has initial SG of 1.000, but this doesn't exist!

terryc...@gmail.com

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Oct 15, 2023, 6:00:04 PM10/15/23
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Thanks for the replies Andrew and Claude. I am certainly no biochemist however the Long Ashton paper opened my eyes to wht goes on in the final stages of fermentation. Having digested Claude's reply i worked my way through the arithmetic in his Table14.4.  That little exercise "revealed all". 
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