Thermal Conductivity Of Corn Mash

This section describes how to distill the 20L of strained corn mash from the chapter on Fermentation to produce about 2L of pure corn whiskey at 45% alc/vol and about 920 ml of feints at 91% alc/vol. The distillations will be carried out using the still or stills described in the chapter on Equipment.

Transferring the Mash to the Still: After the mash has been strained it can be transferred to the still. However, it's useful to cover the strained mash and allow it to settle for two or three hours. This will allow the suspended yeast and very fine mash solids to settle out, leaving a clear yellow liquid, with the suspended solids packing down to a sediment about 8 cm (3") deep. The clear liquid can be siphoned off the sediment into another container, or directly into the still.

If an adjunct of feints is to be included in the distillation run, it should be mixed with the mash or low wines before siphoning into the still.

To transfer the mash to the still place the mash container about half a meter to a meter (1/' to 3') above the top of the boiler. Connect the filler-hose to the top ball valve on the still. Open the top ball valve (make sure the bottom one is closed), and place the siphon starter in the mash. Pump the siphon starter until the siphon starts. Allow the mash to run into the still. When it's finished, close the ball valve and remove the filler-hose.

Transferring Low Wines to the Still: Low wines are typically about 40 to 50% ethanol. This concentration of ethanol will dissolve acrylic. Unfortunately, a lot of home winemaking equipment, such as siphon starters, are made of acrylic and cannot be used in contact with low wines.

In the event that you can't find a siphon starter made of alcohol-resistant material, the low wines can be transferred to the still by placing the filler-hose with the siphon-starter removed in the low wines, opening the top ball valve (ensuring the bottom one is closed), and sucking on the end of the filler-hose with the garden-hose fitting. When the filler-hose is nearly full of low wines, pinch the tube, and quickly screw the fitting to the upper ball valve. After the fitting is secure, release the pinch on the tube and the low wines will flow into the still. When it's finished, close the ball valve and remove the filler-hose.

This will likely require more than one try, and may result in a small spill of low wines.

Before long, you should be able to locate an alcohol-resistant siphon starter.

Measuring Alcohol Content: Measuring alcohol content is done by using an instrument called a "proof hydrometer". A proof hydrometer is essentially measuring the Specific Gravity (SG) of the liquid but presents the reading on two scales: alcohol percentage; and, alcohol proof. They're calibrated based on the assumption that the liquid being measured is a mixture of ethanol and water and nothing else. And, for distilled spirits this is a very safe assumption. It's important to note that a proof hydrometer cannot be used to measure the alcohol content of mash, wine, beer, or any undistilled form of beverage alcohol. Such beverages contain residual sugars and acids and many other compounds that radically alter the SG, and hence a proof-hydrometer measurement.

In this text the term "proof" as a unit of alcohol content has been avoided in favour of "percent alcohol". There are at least three different proof scales, and each one requires mental arithmetic in order to be meaningful. So, for simplicity all references to alcohol content will be expressed as percent alcohol by volume (i.e. % alc/vol).

To use a proof hydrometer, collect a 250-ml sample of the spirit to be measured in a 250-ml graduated cylinder (a 250-ml graduated cylinder holds 300 ml) and float the proof hydrometer in the sample. Next, read the alcohol content off the percent alcohol scale.

Alcohol volume is very sensitive to thermal expansion and contraction. Proof hydrometers are calibrated at 15.56oC (60oF) and a variation of only a few degrees from this temperature will skew the measurement dramatically. So, to obtain an accurate measurement, the temperature of the sample must be adjusted to 15.56oC (60oF).


Beer Stripping (optional): The first step is to do a crude primary distillation on the corn mash. This can be done using a beer stripper as described in the chapter on Equipment. However, many home distillers do not bother building a beer stripper and simply use the spirit still with the needle valve set to almost maximum flow rate to effect a primary distillation.

The purpose of the beer stripping is mostly to facilitate the operational efficiency of the process. It enables a large volume of mash to be reduced to a more manageable volume of higher percent alc/vol to be processed in the spirit still. A distiller could even save the low wines from several beer-stripping runs, then do one big spirit-run on the accumulated low wines, this way contending with only one set of transition points between phases of a single larger run.

However, a primary distillation is not essential to the production of whiskey. One could simply conduct a spirit-run on the fermented corn mash, and bypass the beer-stripping run entirely. In fact, many distillers including the author contend that whiskey made by a single spirit-run produces a more complex and more natural flavoured whiskey than one produced by the customary two distillations. So, the beer-stripping run is optional. Larger scale operations would typically do better with a beer-stripping run, in that it is more operationally manageable. But, if you are doing a small run such as a single batch of corn mash as produced in the chapter on Fermentation, skipping the beer-stripping run and going straight to the spirit-run is most likely the best and easiest way to go.

There are two ways to do a beer-stripping run. One is to use a beer stripper made from a 113L electric hot-water heater as described in the chapter on Equipment. Transfer the corn mash to the beer stripper, close both ball valves, start running cold water through the condenser, and turn on the electric current. Place a suitably sized receiver under the output of the beer stripper. You will be collecting between 3 and 3^L of low wines for every 20L of 8% alc/vol corn mash you place in the beer stripper. With a 3000W heater, 60L of corn mash will come to boil in less than two hours, and then low wines will start flowing from the condenser.

The temperature of the vapour coming over from the boiler at the start will be about 80oC (176oF) and will rise to 98oC (208.4oF) or so as the ethanol in the boiler becomes exhausted. 60L will take about 2^ hours. Although there will be a little ethanol remaining in the boiler at this point, the amount will be too small to warrant the cost of the electricity to drive it over.

The other way to do a beer-stripping run is to use the fractionating spirit still described in the chapter on Equipment. If you are only doing between 20 and 40L batches of corn mash, this is probably the most practical way to go, rather than going to the expense of building a beer stripper.

To use the spirit still, transfer the corn mash to the boiler, close both ball valves, start running cold water through the heat exchanger, and turn on the electric current. Place a suitably sized receiver under the output, and open the needle valve approximately half way. If you are stripping the 20L of corn mash from the fermentation section, a 4L (gallon) jug will make an ample receiver for the low wines. With a 750W heater, 20L of corn mash will come to boil in about 3^ hours, and then the low wines will start dripping from the needle valve. When you observe the low wines dripping into the receiver, open the needle valve all the way and then close it slightly so the distillate is flowing at noticeably less than the maximum rate. This is to prevent loss due to uncondensed vapours escaping out of the needle valve by ensuring that liquid is backing up on the needle valve. 20L will take from 5 to 6 hours to strip.

Spirit-run: The spirit-run is the distillation that produces the finished whiskey, and requires very careful attention to equilibration, flow rate, transition points between phases, and measurements of quantities of the phases collected. Because of this, the description of the procedure will stay closely focused on the distillation of the 20L of fermented corn mash produced in the previous chapters, and on using the spirit still described in the chapter on Equipment.

If a beer-stripping run was performed, load the low wines into the spirit still. There must be at least 5L of liquid in the still to ensure the heating element is immersed at all times. If there are less that 8L of low wines, simply top the volume of low wines up to 8L or so with water. 8L ensures there will still be 5L in the still at the end of the spirit-run. This will make no difference to the flavour or quality of the finished whiskey. If no beer-stripping run was performed, then load the fermented corn mash into the still.

An adjunct of feints should be mixed with the low wines or corn mash before it's loaded in the still. 500-ml makes a good proportion for the 20L of corn mash. However, if this is the first time you have ever done a spirit-run you won't have any feints to add. This is alright, you can go ahead and do the distillation without feints. The flavour of the whiskey will still be good, but will lack body and intensity of flavour and will have a discernable raw alcohol flavour that renders an unbalanced character to the whiskey. Anyway, after this run you'll have feints for all future runs.

The output from the spirit-run should be carefully recorded in a table such as the one in Figure 1. A blank copy of this table is provided as "Appendix C" and can be photocopied for this purpose.

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  • antero
    How transfer corn mash to the still?
    8 years ago

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