Sunday, March 11, 2007

Keeping the Wort Cool in Hot Climates

Son of a Fermenter Chiller - (SoaF)
In the last post I was looking at ways to keep the wort cool during fermentation and conditioning phases of brewing. Some homebrewers I chatted with told me about the "Son of a Fermenter Chiller" which is an insulated extruded polystyrene box which can be easily made from a 4x8' sheet of 2 inch polystyrene.

I found the plans online, in PDF format, by Googling "son of a fermenter chiller". After reviewing the design, I have come up with something similar, but my idea uses two cardboard boxes and that junky white polystrene that is found in electronics and appliance packaging.

By placing a cardboard box inside of another larger cardboard box we create a gap that can be filled with broken bits of beadboard (white styrofoam). The R value we want can be determined by the difference in the box sizes. The SoaF design uses dense 2 inch extruded polystyrene which has an R value of 5 per inch. [R Value Table] The table at the web site suggests that beadboard has an R value of 4 per inch. An effective and efficient R value would be above R10, so I will try for a gap to fill of better than 3 inches. Four inches of beadboard would give an R value of 16 which would be super for the warm temperatures here.

The chiller is "powered" by ice. More accurately, old PET bottles filled with water, capped, then frozen in the freezer. The SoaF designer recommends "gallon" bottles, which are very big for our Philippines sized freezer, so I will try for 1.5 to 2 litre sizes. These can hold about 70% of the water capacity to allow for the ice to expand.

With the cooled wort in the chiller, bottles of ice are added to keep the temperature cool for fermentation in the yeast's recommended temperature range.

A thermostat and small fan from a computer surplus shop, connected to a DC adaptor can be used to circulate the cool air inside the chiller. It's low voltage, safe and cheap to run.

This fat walled, two box design (at R16) should prove to be very efficient and will need less ice than the standard SoaF design, therefore saving on the electric bill too. I also like the idea of re-using that ugly white garbage that floats around the country and takes 300 years to breakdown in the landfill. We can all do a little bit more to keep the country beautiful di ba?

Working the Temperature Differential
The SoaF can be routinely used to create temperature differentials (from inside the chiller compared to the outside the chiller air temps.) of 17°C. This means on a warm day of 35ºC here, a relatively cool temperature of 18ºC can be maintained. This would be most effective for ale yeasts and should produce good results.

By selecting yeasts with higher maximum fermenting temperatures, we can take advantage of the energy savings too. A good ale yeast (saccharomyces cerivisae), from lets say Wyeast, DCL, or White Labs will typically have fermenting temperature ranges of 16 to 24ºC. The higher the temperature during fermentation the more fruity esthers and undesirable by-products are produced, so keeping to the low end of the temperature range will produce the results we want.

Lager yeasts (saccharomyces uvarum) operate a much lower temperature and will require much more energy going into making ice bottles. Perhaps, we can maintain temperatures (8 to 12ºC) for a week or two, but is it really worth the extra energy? In my experience, lagers don't usually ferment as quickly as ales in their respective temperature ranges.

When I get the basic design done on the chiller, I will do some temperature experiments and post the results.

Tomorrow I'll be working on locating equipment and reseaching some sources of ale yeasts online.

Cheers and happy brewing.

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