Soda: Fermentation dynamics and off-flavours

I came here not only to solve my off-flavour issue, but also to learn more about early stage of fermentation. I am making sodas (mostly Ginger Beer) which I am fermenting for carbonation. Everything went well all winter and I didn't have an issue, but suddenly, two batches in a row, I am smelling and tasting solvent like/nail polish off-flavour. According to the descriptors it seems like it could be ethyl-acetate. The recipe I am using stayed the same, I suppose this could have something to do with the dynamics of the fermentation.

My variables are following: I have a 13 Brix solution made with inverted cane sugar (its taste is part of the drink's signature) and I am pitching it with 2.5g of EC-1118 per 10 litres. What has changed is temperature. In the winter I have put the fermenter in the warmest place in the house (+/- 21 °C), now that the heating is turned off, the temperature has actually dropped to around 17 °C. The fermentation is noticeably slower. The usual 24 hours in the primary produced less froth and the finished soda is less carbonated after similar time in the bottle (i usually pasteurise after 16-20 hours of in-bottle carbonation, staying rather on the safe side)

What seems a little counterintuitive is that most discussions and resources online point to high pitching temperatures as the main culprit. Others say that actually low temperatures actually help the production of esters. One resource hinted me at the concurrence of high metabolism and low growth rate. However my current sugar content should be a piece of pie for the EC-1118, so I wouldn't think this is high SG problem.

Should I just pitch more in lower temps? Or should I avoid lower temps altogether? I have rejected the idea of too much aeration, I doubt the yeast would respire with this much sugar. Am I missing something? Thanks for discussing, I am keen on learning more about the mechanics of the process:-)

Topic pitch soda carbonation off-flavor homebrew

Category Mac

1
answered at

Agree with Evil Zymurgist 100% but wanted to emphasize something. I've never heard that lower fermentation temps will encourage ester production. Also, definitely use a hydrometer for any level of precision. Forty hours is enough time to ferment a significant percentage of your sugars. I'd be willing to bet you've probably been getting a higher alcohol content than you've been assuming.

1
answered at

13 brix / 1.050 SG and 21°C/69°F in a 10liter / 2.6g batch your yeast is going to go nuts leaving almost no residual sugars and make the complex alcohols making the nail polish (solvent-like) off flavor, and a 4-5%ABV "soda" if allowed to complete.

Generally a ginger beer uses a "ginger bug" that ferments just enough to carbonate. Or is stopped by refrigeration or preservative.

Basically that recipe has way to much fermentable sugar and too high of a temperature to keep the growth phase slow.

Rather than using time as a marker for when you stop fermentation, take gravity readings and terminate when you get your 0.5-1%ABV.

Alternatively you can reduce the fermentables then add sugar after pastuerizing.

A "FULL" pitch will skip the growth phase and the need for oxygen. So yes more yeast at lower temp will be much cleaner.

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