Coling after primary fermentation
I'd like to hear the forums experience (in ale fermentation) about the + or - about a fast coling down with heat exchanger or a slower coling odwn in the maturation tank.
Bit of a lengthy answer, but there is a lot to consider -
The main considerations are to get (a) the correct yeast portion cropped in sufficient quantities to repitch, (b) to get the flavour right before cooling (c) the final gravity as desired.
Assuming you have not put the cooling on before the final gravity is as desired (and achievable), then we only need concern ourselves with cropping and final flavours. If the yeast is bottom cropping, (and you are using conical bottomed fermenters) then it will probably drop out of suspension once the fermentable sugars are in limited quantities, that is you are near to the final gravity (again assuming the mash pH is correct and your final desired gravity consists almost wholly of unfermentable sugars). Under these circumstances, you should crop the yeast as soon as it forms a consistent slurry, and not leave on for a few days to settle just that little bit further.
Having got the final gravity right and the yeast cropped, then the main concern is flavour, particularly the removal or otherwise of VDKs (vicinyl diketones), principally diacetyl, which gives the beer a butterscotch flavour in high concentrations, and at low but detectable levels may provide a certain richness and fullness to the flavour. Cooling to a diacetyl rest temperature, typically 16 to 19 deg C (according to top heat and yeast characteristics) as soon as down to gravity is OK, but if you cool immediately to filtration temperature, you may leave large quantities of diacetyl in the beer. If this is the flavour you desire – fine, but if not, then you need to either leave at top heat or at a diacetyl rest temperature until these products have been converted to less flavoursome compounds, and the beer flavour is as desired.
Once the PG is down to spec, the yeast has been cropped, and you have got the flavour you want, then the beer should be cooled rapidly to prevent further changes, and to start the sedimentation of suspended yeast, proteins etc. The best way of achieving consistent cooling is to cool through a heat exchanger. Assuming you are going to filter this, aim for a temperature of not more than minus 1 deg C. If you cool in vessel, you tend to get uneven cooling, those layers of beer next to the cooling jackets possibly freezing onto the cooling jacket surfaces, reducing heat transfer further, and increasing losses. Also, like water, beer suffers from lower density below approx 3 deg C, so cold beer rises to the top of the vessel. If your temperature probe is part way up the vessel, then the top can be a block of ice, and the lower part still only 3 deg C. Use of a heat exchanger system can mix everything thoroughly, reducing this risk.
Finally, removal of residual yeast and proteins etc. is much faster and more effective at low temperatures. If you cool the beer rapidly, you can have your beer at the desired temperature for longer and improve the stability, or you can reduce the overall vessel residence time by the time it would otherwise have taken to cool down slowly in the vessel, using the vessels own cooling systems, potentially a large cost saving.
You need to ensure that the heat exchanger, pumping systems etc are thoroughly hygienic, properly cleaned and sterilised before and preferably immediately after use.
The transfer system must not allow any oxygen pickup at all – so all joints must seal properly, pumps must not suck in air, all mains should be purged before transfer with water or inert gas (CO2 or nitrogen) and the beer pushed out after transfer with ideally, deaerated water to prevent air pickup. Once oxygen gets in cold beer it is a flavour disaster in the making if allowed to remain in it and must be removed immediately, probably by gas washing with CO2, though of course this doesn’t do the beer much good either. In other words make sure it doesn’t get into the beer.
Hope this helps
A lot depends on your cooling characteristics, but basically
in ALE fermentation, the following schedule is used:
pitching: lets assume 65*F
primary fermentation 65*F for ~ 4 days
your brew reaches end-fermentation
cool to 50*F (24 hours)
hold at 50*F for 48 hours, than take the ales for your casks
and pull trub and yeast
than cool to 32 *F and hold at 32*F for a minimum of 5 days.
Hope this helps,
Fred M. Scheer
A couple more thoughts that were not obviously clear the first time round -
We, in common with many ale brewers using conicals, cool down to a few dgrees C in fermenter at the end of fermentation, after yeast off etc., but pretty rapidly, at at least one deg C / hr. This is without a recirculation loop. Basically this is because with large numbers of vessels, we cannot guarantee being able to transfer to maturation vessel immediately the beer is available and it reduces the size of the chiller required. However it does rely on reliable properly positioned temperature probes. Target temperature is typically 2 to 4 deg C according to brewer. The beer is then transferred to MV via chillers, down to minus 1 or 2 deg C.
Some brewers using the unitanking system do have a recirculation loop through a chiller - so can cool rapidly in the same vessel, just using the cooling jackets to maintain temperature once down.
If you transfer beer from a comparatively warm FV without chilling on transfer into a maturation vessel in a cold store room with room blast cooling, rather than individually cooled vessels, (as I have seen done at a few places) then there is a risk of the existing beer being warmed up as the cooling system attempts to do its stuff. This rather negates the point of cold conditioning prior to filtration, but is perhaps not so critical if you are going to send out beer as naturally conditioned product.