What are cuts and why do we do them?

[woodduck]

What are cuts?

Cuts are a process by which you remove or cut out a portion of the distilled alcohol in order to eliminate unwanted components and improve the quality of the end product.
Cuts need to be done on every recipe and every still type when performing the spirit run for a final, drinkable output. Cuts do not need to be performed on stripping runs (but you can still cut the foreshots).

How to cut(link)

Why do I need to cut?

Home brewers and distillers use yeast in fermenting sugars to produce alcohol.
Just like any other living organism, yeast eats and produces waste as it grows. Humans get rid of our waste down the toilet(preferably!), but yeast output their wastes right into the fermenter. Luckily for us, alcohol, specifically ethanol is one of those waste products when yeast don’t have oxygen. But yeast also produces a bunch of other wastes, some good, some bad.

Beer is consumed at low levels of alcohol, and if not fermented well, these waste products will be noticed in the taste of the product. Distilling concentrates both the good and bad elements, making them much more noticeable and having a greater effect on the human body.

Controlling your fermentation, in PH, quantity of sugar, levels and types of nutrients, can reduce (but never eliminate!) the quantity of bad waste products. There is no recipe or yeast that does not produce waste. Extra stressed yeast can make more or worse wastes.

Slow distilling via a well controlled spirit run can separate a reasonably good portion of these bad waste products. The process of removing the bad from the good in your product is taking cuts, and it needs to be done regardless of the type of still being used. The very first cut to take is the foreshots, which contains mostly acetone and methanol.

Managing your ferment (link)
Fixing a stuck ferment(link):

How much do I need to cut as foreshots?

As described above, foreshots at most volatile (earliest boiling) compounds in the wash, including acetone, methanol and a number of other esters and aldehydes. Quantities of these volatiles as foreshots will vary based on the type of wash, with fruit based washes having potential to be much higher than cereal grain based washes due to enzymes from fruit digesting pectin to produce methanol. Stressors (temp, high sugar, high ABV,etc) during the ferment can cause greater quantities of volatiles.

As every wash fermented is different, estimating the exact quantity of foreshots is impossible. However, Information on quantities produced are hard to come by. From some sources below, I have approximated acetone and methanol up to about 142ml in 25L wash made with Apple or high pectin content (Agrave, plums,etc), and there are other nasties in there as well as those. In a pot still, the foreshots will be smeared with early heads, and I would recommend disposing of an extra 50% of this quantity for fruit washes.

Grain based washes will be lower, but regardless of the actual quantity produced, the worst of the heads are immediately after the foreshots, and the general rule of thumb is to dispose of a minimum of 150ml per 25 litre ferment. You're cutting for quality, not quantity, so any slight loss of headsy product should be regarded as guarantee of safety and improvement in quality.

TLDR; 150ml/25L for cereal washes and 225ml/25L for fruit based washes.

Tell me more!

Yeast produces a lot of products through digestion of sugars, and interactions between chemicals occur in the wash. These include:
• CO2
• Acetone
• Higher alcohols/fusel oils, including methanol (Toxic alcohols. note: fusel means bad liquor in german)
• Ethanol (drinkable alcohol)
• Acids (organic/fatty)
• Esters (flavour – these are reactions of acids and alcohols)
• Aldehydes (oxidised alcohols) & ketones
• Sulfur containing compounds (sulphur dioxide, hydrogen sulphide, dimethyl & diethyl sulphides

How much of each of these gets produced depends on level of sugar, health and state of the yeast during ferment, temperature, pressure, aeration, nutrient levels and a host of other factors. See the ferment management link above for more information.

Cuts are possible because different chemical compounds boil at different temperatures, and therefore come at different times in your stilling run. Here are some of the boiling points for products produced in wash:

• Acetone 56.5C
• Methanol 64C
• Ethyl acetate 77.1C
• Ethanol 78C
• 2-Propanol (rubbing alcohol) 82C
• 1-Propanol 97C
• Water 100C

In a wash, these products are not pure though, they are all mixed together, which changes the boiling point. Some of these mixes are called azeotropes, where the boiling points of two products combined are different to each individual boiling point. This can be pretty complicated, as azeotropes will form between alcohols and water, esters and water, alcohol and esters and so on.

azeo.gif

This shows an azeotrope boiling point for water/ethanol mix based on percentage of ethanol in the mix. One of these charts would be possible to plot for each azeotrope. This is just to show nothing is a straightforward boiling point when you start dealing in complex systems.

What this means in practice is that when you take cuts, there will be smearing(less separation) of these compounds over time rather than evaporating exactly when the boiler hits that temperature. The faster the run, the more smearing there will be.
Acetone and methanol form an azeotrope that boils at 56.5 C, methanol and water at 64.7, and these form the big part of the foreshots, along with methyl acetate (50.5C). Ethyl acetate/water azeotrope boils at approx. 70.4C, at this will form a big part of the early heads.
The esters that are produced are responsible for a lot of both the good and bad flavours in a wash. If you’re producing a neutral, you’ll want to cut as much of these as you can, but in brown spirits some level of late heads/early tails can be beneficial to the finished product.

Some distillers add microbes to their wash, which can result in yeast producing more acids to fend off the microbes. These acids react with alcohols to form more esters, which means more flavour. Finding the right strain and balance for good flavours must be tricky.
Because of the magnitude of chemical reactions in the wash, it is almost impossible to determine by temperature or mathematically when the cuts should occur or exact volumes of heads or tails. You can however, get a good feel from previous runs of the same recipe if fermented in a similar way. From what I can gather, most commercial distilleries still operate by taste and smell of the product around where they expect the cuts to happen. Based on the taste of some products, some commercial producers don’t cut at all :puke-huge:

The bottom line is cuts are an essential part of making your product safe, headache free and of a higher quality than you would otherwise produce. Be safe and enjoy! :happy-partydance:

There are some azeotrope tables here:
Azeo details
Azeo data tables

I based my approximations on worst case foreshots figures from the following sources:
Methanol contamination article
Brewing from a chemist's standpoint