Grain procurement for distilleries

Distilleries buy starch, not grain

Yeast cannot ferment starch directly. Enzymes break the starch into sugars, yeast turns the sugars into alcohol and the still separates the alcohol out. So what a distillery is really paying for is fermentable starch. The rest of the grain, the husk, protein, fibre and water, goes out as spent grain or effluent.

That is why grain buyers talk about starch content and moisture as much as price. Two lorries of maize at the same price per tonne can give very different amounts of alcohol if one is wetter or lower in starch. Our guide to the grains used in whisky explains how each cereal behaves.

The theoretical yield sets the ceiling

Chemistry puts a hard limit on how much alcohol a tonne of starch can give. When starch breaks down to glucose it picks up water, so one tonne of starch gives about 1.11 tonnes of glucose. Fermentation turns glucose into ethanol and carbon dioxide. By mass, about 51% of the glucose ends up as ethanol.

Put together: 1 tonne of starch x 1.11 x 0.511 is about 568 kg of ethanol. Ethanol weighs about 0.789 kg per litre, so that is roughly 720 litres of pure alcohol per tonne of starch. No distillery reaches that figure, because some sugar feeds yeast growth and some starch is never converted. But it is the number every real yield is measured against.

For a grain that is roughly two thirds starch, the ceiling is therefore somewhere under 500 litres of pure alcohol per tonne, before real-world losses.

The specification sheet, line by line

• Moisture. Water is weight you pay for and cannot ferment. Wet grain also heats up and moulds in storage. Grain is usually bought at around 12 to 14% moisture or less, with price deductions above the agreed limit.
• Starch. The higher the better for yield, measured by a laboratory test on samples.
• Foreign matter and broken grain. Stones, dust and chaff add weight without starch. Some damaged grain is acceptable for distilling, which is why broken rice is widely used.
• Mycotoxins. Toxins from moulds, such as aflatoxin in maize, are a quality and safety concern because they concentrate in the spent grain sold for cattle feed.
• Insect damage. Infested grain loses starch and spreads pests through the store.

Indian distilleries use a wide range of feedstocks

Much of India's spirit has historically been made from molasses, the syrup left over from sugar making. Grain distilleries use broken rice, maize, sorghum, millets and wheat, depending on price and availability in the region. Malt whisky distilleries buy malted barley from maltsters instead, often made from Indian six-row barley.

Grain buying in India has become more competitive. The national programme to blend ethanol into petrol uses the same molasses and grain that potable alcohol distilleries need. When fuel ethanol demand rises, feedstock prices and availability for drinks producers move with it. Government policy on grain sales for ethanol has also changed several times, so buyers watch it closely. Our guide to molasses and grain spirit compares the two routes.

Storage is part of procurement

Buying good grain is only half the job. It has to stay good until it reaches the cooker. Grain is alive in a sense: it respires, gives off heat and moisture and attracts insects. In a silo or godown, a warm, damp patch can spread and spoil a large part of the stock.

Indian conditions make this harder. Monsoon humidity raises the moisture of stored grain. Summer heat speeds insect growth. Distilleries manage this by checking temperature and moisture in storage, turning or aerating grain, fumigating under controlled conditions and using stock first in, first out. Buying large volumes at a low harvest price only saves money if the storage can hold it without losses. A procurement plan that ignores storage capacity and condition is really a plan to buy spoilage.

How grain is bought and checked

Distilleries buy grain through a mix of routes: traders, local markets, tenders, government sales of surplus stocks and forward contracts with suppliers. Larger producers spread purchases across sources and seasons to manage price and supply risk.

The floor detail that matters most happens at the gate. Every lorry is weighed in and out on a weighbridge, sampled with a probe from several points in the load and tested for moisture before it is unloaded. A load that fails the moisture or foreign matter limit is rejected or priced down on the spot. A buyer who has never watched that process will struggle to understand why invoiced tonnes and usable tonnes differ.

Yield per tonne is the number that links the desk to the plant

The key measure is litres of alcohol per tonne of grain. It brings together grain quality, how well the plant cooks, converts and ferments the grain plus how much alcohol the stills recover. A fall in that number can come from cheaper grain, a fermentation problem or a measurement error. Our guide to litres of alcohol per tonne as a KPI explains how to read it.

This is where procurement and production meet. The cheapest grain per tonne is not always the cheapest grain per litre of alcohol. A first step is simple: put price per tonne, moisture, starch and the plant's yield for each supplier side by side for the last six months, then calculate cost per litre of pure alcohol by supplier. The ranking often changes.

Common questions

How much alcohol does a tonne of grain give?

In theory about 720 litres of pure alcohol per tonne of starch. Real yields are lower and depend on the grain's starch content and how well the plant converts and ferments it.

Why does grain moisture matter so much?

Water adds weight without adding alcohol. Wet grain also moulds and heats in storage. Contracts usually set a moisture limit with deductions above it.

What grains do Indian distilleries use?

Broken rice, maize, sorghum, millets and wheat for grain spirit, malted barley for malt whisky and molasses for much of the neutral spirit.