Dry Chilli and Spice Cold Storage: Colour, Aflatoxin and Humidity Control

Reference tables (ASHRAE, USDA Handbook 66) list dried chilli at 0–10 °C and 60–70% RH for about six months, and Indian commercial stores work in the same band, often holding stock longer until prices or the next season justify release. The same logic of cool, dry and dark applies to other dried spices:

Do not confuse dry chilli with green chilli: the HyperCold temperature chart lists green chilli as fresh produce at 90–95% RH, conditions that would push dried pods into the mould range. Values vary by variety, drying method and buyer specification, so treat these as working ranges.

Buyers grade dry chilli mainly on colour, measured as extractable colour in ASTA units, and on pungency. The red colour comes from carotenoid pigments such as capsanthin, which break down with heat, light, oxygen and moisture; colour is the quality lost first in warm storage. Pungency comes from capsaicinoids, which are more stable but also decline slowly over long, warm holding.

Cold, dark storage slows pigment breakdown, and that is the main commercial reason chilli goes into cold storage rather than an ambient godown. Moisture has to be balanced as well: over-dried pods turn brittle and break during stacking and handling, and broken pods fetch a lower grade, while under-dried pods risk mould. Keep the chamber dark, switch lights off when nobody is inside, and avoid temperature swings, which also drive moisture movement inside the bags.

Dried chilli is hygroscopic: over time its moisture balances with the surrounding air, and its water activity settles close to the room RH divided by 100. A pod held at 65% RH ends up near a water activity of 0.65, below the range where the moulds that matter grow. Aspergillus flavus, the main aflatoxin-producing fungus, generally needs a water activity of roughly 0.8 or more and grows and produces toxin best at warm temperatures. Ambient godowns in humid monsoon weeks, at around 30 °C and 80% RH or more, supply both conditions; a chamber at 0–10 °C and 60–70% RH removes both.

Cold storage prevents; it does not cure. Aflatoxin already formed during slow drying, drying on bare soil or rain-wetting stays in the pods, so quality starts in the field: dry quickly on clean tarpaulins or drying yards, and bring chilli into storage only once it is properly dry. FSSAI and importing countries set maximum aflatoxin levels for chilli, and some export markets apply stricter limits than others; check the current limits for each market before storage and sale.

Insects are the other storage threat in dry chilli. Most stored-product insects slow down sharply below about 15 °C, so a cold chamber also protects against infestation, provided lots come in clean. Any fumigation must be done by a licensed pest-control operator under current rules.

Guntur in Andhra Pradesh is a major dry-chilli growing and trading centre, and the district has a large cluster of cold storages that hold chilli for farmers and traders between harvest and sale. Chilli is harvested and sun-dried in the dry months early in the year, and holding it until later in the year, when prices are often better, means carrying it through a hot summer and a humid monsoon: exactly the conditions that fade colour and invite mould. Neighbouring chilli belts in Telangana and Karnataka follow the same pattern.

Many of these stores work on rent, holding lots from many farmers and traders in one chamber, so lot identification and lot-wise access matter as much as temperature. For local project support, see HyperCold's Guntur page.

A chilli chamber is a dry room: the target is 60–70% RH, and nothing in it should add moisture. At a 4 °C setpoint and 65% RH the room dew point is about −2 °C, so the evaporator coil, running colder than that, removes moisture whenever the compressor runs. Control problems come from the gaps: off-cycles, defrost, door openings and warm, humid air entering during loading and dispatch in the monsoon. The design response:

• Control on RH as well as temperature, with a logged humidity sensor and a high-RH alarm.
• Select the evaporator for dry-room duty, drain defrost water out of the chamber, and add a desiccant dehumidifier at humid or coastal sites.
• Never fit a humidifier, and never wet-clean the floor during the season.
• Use an ante room so doors do not open straight to humid ambient air.
• Warm dispatch lots gradually: cold bags taken into air at 30 °C and 80% RH, which has a dew point of about 26 °C, condense water on their surface at once, and damp bags in a warm truck are an easy start for mould.

The principles are the same as in a seed cold storage, where separate humidity and temperature control is standard. Dehumidifiers are priced after the site survey; they are not on HyperCold's standard rate card.

Dry chilli should not share a chamber with fresh produce or with other spices, for five reasons:

1. 1Humidity — fresh produce rooms run at 85–95% RH, which would push dry chilli into the mould range.
2. 2Odour — chilli pungency taints other goods, and spices such as cardamom and cumin pick up foreign odours.
3. 3Dust — capsaicin dust irritates eyes and airways, so chilli chambers need their own air circuit, and staff need masks and eye protection when handling stock.
4. 4Insects — one infested lot can spread to clean stock; separate chambers contain it.
5. 5Fire load — dried chilli in jute bags is combustible, so aisles, detection and firefighting access have to be planned for it, and the building must meet fire NOC requirements (see cold storage compliance).

Each dedicated chamber gets its own evaporators, so no return air passes between commodities, along with its own setpoint and RH control.

Chilli is stored in bags stacked lot by lot. Practical rules:

• Stack on pallets or wooden dunnage, never directly on the floor.
• Leave 100–150 mm from walls and a 300–450 mm gap below the ceiling, as HyperCold's capacity model assumes.
• Keep a main aisle for pallet trucks or trolleys, plus inspection aisles between lot blocks, so every lot can be sampled, checked for insects and removed without shifting others.
• Limit stack height so the bottom bags do not crush pods into broken grade, and keep stacks stable.
• Tag each lot with owner, date in and moisture at intake, and dispatch first-in, first-out unless the owner decides otherwise.

Capacity uses the configurator's formula, gross volume (m³) × usable fraction × as-stacked bulk density (kg/m³) ÷ 1,000, but dried chilli is not one of the configurator's listed commodities. It is light and bulky, well below the 500 kg/m³ default the configurator uses for general produce, so use your own measured density: weigh a stacked bag and divide by the space it occupies. At the palletised-room usable fraction of 0.62, each 100 kg/m³ of as-stacked density gives about 12.6 MT in a 30 × 20 × 12 ft chamber (204 m³).

Also ask for the RH target, dehumidification method, defrost drainage, fire detection and aisle plan in writing. Final pricing depends on the site survey; build a chamber-wise BOQ in the quotation configurator.