Benefits or downsides of cooler fermentation for ales

[fullclaret]

Morning,

I know high fermentation temp can produce some unwanted fusol alcohols, but apart from a stalled fermentation what harm can a low temp fermentation cause? I'm using Wyeast strains that recommend pitching at 23 then cooling once fermentation starts. They list a range of around 15-23oC depending on the strain. Some of my darker ales end up a bit twangy (not very descriptive I know), so I thought I'd try some lower temps a degree or 2 below the recommended minimum is this wise?

Cheers,
Steve

[AnthonyUK]

I fermented a Wherry recently at 18°c and whilst perfectly acceptable I think it is a bit bland. I'll definitely be looking at a bit higher temps. for the next ale.

[gregorach]

They do slow down quite a bit at the bottom of their ranges, and if you go too low, it'll drop early leaving you with less attenuation than you might expect. I'd be reluctant to go much below the specified ranges.

I prefer to pitch a little cool and let it rise to target as fermentation gets going, but I do pitch fairly hefty amounts from fresh propagations and I do use bottled O2... Pitching warm is safer if you're not 100% certain you have sufficient viable cells or you might not have quite enough O2.

Might just be that you're not happy with the specific strain characteristics for a given beer... I'm not really sure what you mean by "twangy".

[TheMumbler]

I think that early fermentation produces more flavour compounds than late, so you might want to try pitching at the bottom end of the range and then bring it up later on to keep the yeast active to get good attenuation, as gregorach suggests.

You would need to ensure that you had enough a big enough starter though, otherwise stressing the yeast by underpitching might cause off flavours.

[Wolfy]

Ferment below the recommended temperature range is likely cause more problems than you are trying to solve, the the yeast might throw other flavours, they may drop out early and not finish fermenting etc.

However, many/most yeast-type-flavours and aromas are generated at the start of fermentation when the yeast reproduce. Rather than pitch warm like you have been, try pitching cooler (say 1 or 2deg below fermentation temp) and then it gradually warm up to your 'normal' fermentation temp over the next day or two. You might well find that this changes the yeast-flavour profile, but it will also allow the yeast to actively ferment your beer without problems.

This is a procedure that I often follow, sometimes even removing the 'heating' side of the temp controller, and letting the heat generated by the yeast slowly warm the fermentor the couple of degrees up to fermentation temp.

[fullclaret]

Thanks for the replies. I'll try and define twangy a bit...

Lacking crisp, clean taste you get from commercial beers.
Can be agressively malty, especially with traditional english ale styles.

I've 2 brews fermented at lower than recommended temps that are conditioning now. I Pitched them warm then wacked in the fridge for a few hours once ferm started, then kept around 17oC. Primary took a full week as opposed to the 4-5 days from previous brews, and S.G. dropped to 1012 on both. Waiting to see how this has affected them as one is a repeat recipe.

I've just started a london pride clone that in the past I've struggled to get close to good as it's been too heavy on the malt and the crisp sweetness was overpowered. I've got that at 17oC and Wyeast say 18-22 for 1968 London ESB so from what you've said I'm not risking the brew too much.

[spook100]

Diacetyl is a by-product of fermentation that is generally considered a flaw. Diacetyl is produced early in the fermentation process and then most of it is reabsorbed by the yeast and reduced to flavourless compounds later on. Keeping the fermentation temperatures on the low side early, and then increasing the temperature later on should result in a decrease in the amount of diacetyl produced while the yeast activity is slightly inhibited by the lower temperature, and then a better reabsorption as the yeast becomes more active as the temperature increases. The down side is that you need a good population of yeast for fermentation to complete properly, and the low temperatures inhibit yeast reproduction. The trick is to pitch a decent, healthy quantity of yeast at the start. I usually make up a 2l starter about 2 days beforehand and pitch at around 16-17c and keep it there until I have reached about 50% attenuation, then I increase the temperature to around 20c for the remainder. I use this method on every batch I make and have never had a stalled fermentation.

[gregorach]

Thanks for the replies. I'll try and define twangy a bit...

Lacking crisp, clean taste you get from commercial beers.
Can be agressively malty, especially with traditional english ale styles.

Ah... Are you perhaps meaning "flavoursome"?

Yeah, try pitching a bit cooler. Also re-examine your hygiene and handling procedures to see if there's anything you could be doing better - a lot of subtle flaws can come from levels of contamination below the point where you'd immediately think of it as a likely problem.

[lupulin]

It sounds to me that you might be lacking full attenuation if your beer is tasting overly sweet or muddy. If that's the case, I would probably pitch and ferment on the warm side (not too warm or you'll get fusel alcohols). If the yeast is dropping out early because of cool temps, that could lead to what you're talking about. What temps are you currently fermenting at?

[fullclaret]

My Pride clones do tend to have lots of diactyl and I've countered that by leaving in secondary at 20oC for 2 weeks before bottling. I find that conditioning out the diactyl created after bottling takes another 2-4 weeks, so it's a 6-8 week process and I'm not that patient. I'd rathre keep the levels low to being with.

Strange thing with the twang is it only happens with darker ales using up to 10% crystal and my usual Marris otter. I brew a summer ale with 10% wheat and 90% MO, using whitbread 1098 yeast and it's always been great (by my own standards ). Same process is followed throughout, except water is slightly more acidic.

All regular beers finish at 1011-1013 depending on style so attenuation's fine.

I'll keep an eye on the hygiene, good call Dunc. I may tend to 'fuss' (stir, check temp etc) over the ales more than the summer brew so another lesson in patience required. One day I'll get an airlock and switch away from plastic bins so I don't have to keep lifting the lid...

Cheers,
Steve

[gregorach]

I'll keep an eye on the hygiene, good call Dunc. I may tend to 'fuss' (stir, check temp etc) over the ales more than the summer brew so another lesson in patience required. One day I'll get an airlock and switch away from plastic bins so I don't have to keep lifting the lid...

I've fitted the lid of my fermenting bin with an airlock, a thermowell and a 1" tank connector (with cap) so I can take samples without actually popping the lid. I line the sampling port with a fresh bit of flamed tinfoil for each use, and I pull my samples with single-use sterile pipettes... Plastic bins are fine (IMHO) as long you avoid scratching them - so no metal spoons and no green scouring pads. They have the advantage of being easy to clean properly... Oh, and cheap.

Only times I've had significant and unexpected diacetyl problems turned out (I think) to be down to picking up excess oxygen when racking to a secondary... Hasn't happened again since I started flushing with CO2 before transfer.

[fullclaret]

Hmm, I feel some quality time required in the garage to fit some bits to the bin lids, I wonder if I could fit a rubber grommet through which the glass tube thermometer would sit and allow readings without moving anything

Airlock sounds good too, I rely on a krausen to know when fermentation has started.

Have you got any pics of your creation, would be good to plagiarise, er, I mean inspire me. )

[gregorach]

Not in it's current state I'm afraid...