By Lukie Pieterse, Potato News Today

Baseline monitoring and decision-making for better storage outcomes

Potato storage is rarely, if ever, “set it and forget it.” In the northern hemisphere, the heart of the storage season is when small, repeated decisions – often made under time pressure – quietly determine whether a crop ships smoothly in late winter and spring, or unravels into shrink, rot, bruising, and costly surprises.

This article forms part of PNT’s Storage Season Essentials series, built for the people who carry the responsibility of the pile – one practical baseline at a time.

A recurring problem across the industry is not a lack of effort or experience – it’s signal-to-noise. Many facilities track too little, track inconsistently, or track data that never gets translated into clear operating decisions. When that happens, a storage becomes reactive by default: managers respond to symptoms rather than steering the system based on early warnings.

This article is designed to reduce that guesswork. Below are ten measurements that – taken together – operate like a practical early-warning system. They work whether you’re running a sophisticated automated system or a more basic storage with handheld tools and hard-earned intuition. The common thread is discipline: consistent measurement locations, consistent timing, and consistent interpretation.

What “predictive measurements” really means

These ten measurements don’t predict the future like a crystal ball. They predict outcomes because they reveal the three forces that ultimately decide a storage season:

• Biology in the pile (respiration, moisture migration, wound healing, breakdown risk, dormancy behaviour)
• Physics in the building (airflow distribution, heat transfer, condensation risk, building envelope performance)
• Human decision-making (fan run logic, temperature transitions, documentation, early intervention)

If you can observe those three forces clearly, you can manage them – and usually prevent small problems from becoming expensive ones.

Pile temperature – not just “a temperature”

A single temperature reading is comforting, but it can be dangerously misleading. Pile temperature is not a point – it’s a profile. What matters is how temperature behaves across the pile: top vs mid vs bottom, centre vs walls, near doors vs deeper zones, and – if you have multiple bays – bay-to-bay differences.

When temperature distribution is stable and predictable, it usually means your storage is functioning as a system. When it becomes patchy or inconsistent, it is often the first visible sign that airflow distribution, moisture movement, or respiration is changing inside the pile.

Why it matters:

• Temperature drives respiration. Higher temperature generally increases respiration – and with it CO₂ production, heat generation, and moisture release.
• Temperature gradients often reveal airflow problems before rot becomes visible.
• Temperature patterns help interpret dehydration risk, condensation risk, bruise sensitivity, and – for processing lots – sugar behaviour and fry colour risk.

What to measure in real terms:

• Use consistent locations. A “random walk and poke” approach makes trend detection nearly impossible.
• If you’re low-tech, choose a simple map: three points per storage zone (front / middle / back) and three depths where possible (upper / mid / lower).
• If you’re higher-tech with probes, treat them like a network. The value is not any single probe – it’s the pattern.

Early warnings that matter:

• A zone that stays warmer than the rest even after comparable fan cycles
• A warm zone that gradually expands week over week
• A top layer that cools quickly while mid-pile lags (often uneven airflow or moisture movement)
• Increasing wall-to-centre differences (often building envelope or distribution issues)
• Sudden temperature “noise” that wasn’t present earlier (often tied to outside swings, condensation events, or changed fan logic)

A practical response mindset:

• Confirm with a second method if possible (handheld check to validate a probe, or vice versa).
• Ask one diagnostic question: is this airflow, moisture, or biology? That decision tells you where to look next.

Supply air and plenum temperature – know what you’re feeding the pile

If you do not know the temperature of the air you’re pushing into the pile, you’re operating blind. Supply air temperature and plenum temperature explain why the pile is drifting – and whether your ventilation strategy is steering you toward stability or toward condensation and stress.

Between intake location, air mixing, ducting, fan heat, and building conditions, the air delivered to the pile can differ from what operators assume. That gap is where “we did everything right” storage seasons often start going wrong.

Why it matters:

• Supply air temperature is the most direct lever for pile temperature transitions.
• Plenum stability is a strong indicator of system consistency and air distribution.
• Supply air that is too cold relative to tuber temperature can drive condensation on cold surfaces.
• Supply air that is “right” while the pile doesn’t respond points to distribution issues, short-circuiting, or sensor placement problems.

What to measure:

• Measure supply air where it enters the plenum, not only at the intake.
• If the plenum is long, measure at more than one point – even one additional point can reveal a lot.
• If you blend air (recirculation + outside), measure after mixing – not before.

What to watch for:

• Supply air consistently colder than the tuber mass during periods of moisture risk
• Zones of the pile not responding to comparable fan cycles (dead zones)
• Plenum temperatures varying widely along the length of the storage (leaks, blockages, uneven distribution)

A useful interpretation rule:

• If supply air looks stable but pile temperatures are diverging, suspect distribution first – not the fan schedule.

Relative humidity – useful, but easy to misread

Relative humidity matters, but it’s often misunderstood. RH is not a “good” or “bad” number by itself – it becomes meaningful only when paired with temperature, airflow, and condensation risk.

A storage can show “good RH” and still experience condensation events. Another can run lower RH and avoid condensation, but pay the price in weight loss, quality defects, and higher bruise sensitivity. The right question isn’t “what is the RH?” It’s “what is RH doing in this temperature and ventilation context?”

Why it matters:

• RH influences dehydration (weight loss) and surface condition.
• Very dry air combined with aggressive ventilation can drive shrink and create quality issues that show up later.
• High RH can stabilize moisture conditions – but it can also contribute to condensation when temperatures cross risk thresholds.

What to measure:

• Track RH at a consistent location relevant to delivered air.
• Be cautious about sensor accuracy. A drifting RH sensor can quietly cause months of wrong decisions.
• If you have multiple zones, don’t assume RH is uniform across the building.

What to watch for:

• Long periods of low RH combined with long fan run time (dehydration and shrink risk)
• RH spikes that align with weather events (moisture ingress, mixing issues, or sensor placement effects)
• High RH combined with temperature swings (condensation risk)
• A mismatch between RH readings and what the pile looks or smells like (sensor error or local conditions not being captured)

Dew point – the condensation risk lens that changes everything

If there is one storage concept that separates calm seasons from chaotic ones, it is condensation control. Condensation is not just a nuisance – it’s often the trigger that accelerates breakdown and turns a manageable storage into a constant triage exercise.

Dew point helps you understand when air will deposit water on cooler surfaces – including tubers, duct surfaces, walls, roofs, and the upper pile. It’s the difference between “RH looks fine” and “this is a sweating event waiting to happen.”

Why it matters:

• Condensation supplies free water – and free water is a friend to rot organisms.
• Condensation can be local, brief, and repeatable. Those are the events operators often miss until quality declines.
• Warm spells are classic dew point traps mid-season when the pile mass is already cold.

How to use it without making it complicated:

• If your system calculates dew point, use it as part of your ventilation decision routine.
• If not, adopt dew point thinking: be cautious any time warmer, moist air is being moved across colder tubers or cold building surfaces.
• Rapid transitions – warm to cold, cold to warm, dry to wet – deserve extra caution and extra inspection.

Where condensation often shows up first:

• Underside of roof structures and at insulation breaks
• Walls near corners and intake points
• Louvers and door zones
• The top layer of the pile, especially near walls
• Stagnant zones where air does not move evenly

What to watch for:

• A “wet” smell or a sudden odour change
• Fogging at openings during ventilation shifts
• Wall frost patterns changing after weather swings
• Dampness on surfaces that were dry previously

Operational response when risk rises:

• Shift from a cooling mindset to a stability mindset. The goal becomes avoiding moisture deposition.
• Consider shorter, more controlled fan cycles during risky conditions rather than long runs that import moisture.
• Increase walk-through frequency during warm spells and after precipitation events.

Carbon dioxide (CO₂) – your biological and ventilation barometer

CO₂ is one of the most underused measurements in potato storage, and one of the most valuable when available. It tells you about respiration in the pile and the effectiveness of ventilation.

Even without perfect “target” numbers, CO₂ trends and zone comparisons are highly informative.

Why it matters:

• Rising CO₂ can indicate increasing respiration, poor air exchange, or dead zones.
• CO₂ differences between zones often reveal distribution problems before quality fails.
• CO₂ can shift before visible breakdown becomes obvious.

How to measure usefully:

• Focus on consistency: same times, same zones, same approach.
• Zone comparisons matter. A stable “good zone” next to a drifting “trouble zone” is a powerful clue.
• If CO₂ is automated, confirm sensors are placed in meaningful air pathways, not just convenient locations.

What to watch for:

• CO₂ creeping upward over weeks
• One zone rising while others remain stable
• High CO₂ paired with warm spots and odour changes
• CO₂ staying high even with long fan runs (often a distribution or short-circuiting issue)

How to interpret without overcomplicating:

• CO₂ is not usually a single-number trigger. It’s a pattern tool: stable or drifting, uniform or uneven, improving or worsening.

Fan run time – and the reason behind it

Fan run time is a measurement and a management philosophy. Two storages can run fans the same number of hours and get very different outcomes depending on air conditions, distribution, and pile resistance.

A key maturity shift in storage management is moving from “fans as habit” to “fans as decision.”

Why it matters:

• Over-ventilation can drive shrink, dehydration, and stress – especially during dry air events.
• Under-ventilation can allow CO₂ creep and hotspots to establish.
• Fan run time without rationale makes troubleshooting and learning almost impossible later.

What to record (minimum viable discipline):

• Fan run hours daily
• The intent behind the run (cooling, equalizing, moisture management, CO₂ control, response to hotspots)
• Outside conditions at the time (even brief notes)

What to watch for:

• Fans running because it’s routine rather than because conditions support the goal
• Long runs during very dry periods (weight loss risk)
• Long runs during warm, moist periods (condensation risk)
• Fan runs producing little pile response (distribution, leaks, blockages)

A small habit that pays off:

• One sentence beside fan run time in the log is often the difference between management and guessing.

Static pressure – the airflow health check

Static pressure is one of the clearest indicators of whether air is moving through the pile as intended. Where it is available, it should be treated as a core measurement, not a technical extra.

Static pressure is valuable because it can show airflow problems before they become quality failures.

Why it matters:

• Rising resistance can indicate blockages, compaction, frost / ice issues, or changed pile permeability.
• Uneven pressure between ducts or zones can indicate distribution problems or leaks.
• Fans can sound normal while effective airflow is compromised.

What to watch for:

• Pressure creeping upward through the season
• Large differences between zones
• Pressure behaviour changing after weather events (ice, moisture shifts)
• Pressure not matching expected fan performance

If you don’t have pressure measurement:

• Treat it as a worthwhile future upgrade in many storages.
• In the meantime, rely on proxies: uneven temperature response, CO₂ differences, recurring trouble zones, and airflow observations at known exits or pathways.

Outside air conditions – not “free cooling,” but a decision input

Outside air can be a gift or a trap. Winter air swings between ideal and risky, especially during warm spells, precipitation events, fog, and rapid temperature shifts.

Outside air should be treated as a decision input – not a default solution.

Why it matters:

• Warm spells increase condensation risk when a cold pile meets moist air.
• Wet air events can import moisture and trigger sweating.
• Cold snaps can shock the pile if transitions are too aggressive.

What to log (simple but effective):

• Outside temperature
• Outside moisture conditions (rain, fog, snow, “damp air”)
• Unusual wind conditions if your building is sensitive to them
• The rationale behind ventilation decisions during unusual weather

What to watch for:

• Problems that line up with warm spells (often condensation-driven)
• Weight loss that lines up with very dry cold air plus long fan runs
• Building behaviour that changes with wind direction (leaks, pressure differentials, short-circuiting paths)

Visual and sensory checks – the human sensor network

Instrumentation is powerful, but disciplined walk-throughs catch what sensors miss – especially when sensors are sparse, drifting, or poorly placed.

This is professional practice, not nostalgia. Your eyes and nose detect early change, particularly around condensation and breakdown risk.

What to look for:

• Roof drip, wall frost changes, damp corners, wet patches near openings
• Unusual airflow behaviour around doors and louvers
• Surface condition changes: excessive drying near air paths, crusting, uneven firmness

What to smell for:

• Sweet, musty, sour, or “off” odours that weren’t there earlier
• Odour localized to one area rather than building-wide

What to do when you detect changes:

• Document immediately (location, time, outside conditions, fan status).
• Cross-check temperature and CO₂ in that zone if available.
• Increase monitoring frequency in the area – issues rarely self-correct.

A storage log – documentation that turns effort into management

If measurements are not written down, they don’t exist in a way you can learn from. A storage log does not need to be fancy – it needs to be consistent.

Logs are not bureaucracy. They are how you:

• detect trends early
• justify decisions
• coordinate staff
• learn season over season
• protect your operation in disputes

Minimum viable logging:

• Date and time
• Pile temperatures in consistent locations
• Supply / plenum temperature
• RH and dew point if available
• CO₂ if available
• Fan run time and the reason
• Notes on odours, condensation evidence, and unusual events
• Notes on known-risk loads (wet, bruised, soil-heavy, late harvest)

What to watch for:

• “We think it started around…” instead of “It started on…”
• No record of weather events and how the storage was run during them
• No record of fan rationale

The long-term payoff:

• A good log turns storage from experience-only to repeatable learning. Over a few seasons, that can improve outcomes as much as many hardware upgrades – because decisions become clearer.

Baseline Checklist: The Daily – Weekly Storage Routine

Daily (or every shift in high-risk periods):

• Record pile temperatures in consistent locations (upper / mid / lower where possible)
• Record supply air and/or plenum temperature
• Record RH (and dew point if available)
• Record CO₂ if available
• Record fan run time and the reason for operation
• Walk-through: check for odours, condensation signs, roof drip, wall frost changes, unusual wet zones

Weekly:

• Review pile temperature patterns and identify persistent gradients
• Compare zones – a single trouble zone often reveals distribution or building issues
• Inspect building trouble points: doors, louvers, corners, roof structures, insulation breaks
• Review fan run patterns and confirm decisions align with outside conditions and crop intent
• Summarize “what changed” this week in one short paragraph in the log

Low-tech vs high-tech – the baseline still works

If you’re low-tech:

• Consistency beats complexity. A handful of reliable measurements taken the same way every time will outperform scattered checks taken only when someone remembers.
• Walk-through discipline becomes more important, not less.

If you’re high-tech:

• Avoid drowning in data. The goal is not dashboards – it’s decisions.
• Validate sensor accuracy and placement. A sophisticated system with weak sensor placement can mislead more confidently than a simple thermometer.

Common scenarios – and how the 10 measurements guide your response

The following scenarios show up in almost every storage season somewhere. The difference between a manageable event and a costly spiral usually comes down to two things: how fast you recognize the pattern and whether your measurements are consistent enough to trust.

Warm spell in mid-winter (the classic “sweating” trap)
What’s happening: outside air warms up and often carries more moisture. Your pile mass is still cold. That temperature mismatch creates a high condensation risk – sometimes inside the pile, sometimes on building surfaces, sometimes both.

What you’ll often notice first:

• A change in smell near doors or vents
• Fogging at openings during ventilation changes
• New wall frost patterns or roof drip behaviour

Which measurements matter most:

• Dew point thinking (condensation risk lens)
• Supply / plenum temperature (what you’re actually pushing into the pile)
• Pile temperature profile (how cold the pile mass really is)
• RH trends (context, not an absolute)
• Walk-through findings (your first “sensor”)

What a sensible response looks like:

• Shift from cooling to stability – avoid long fan runs that import moist air under risky conditions.
• Use shorter, controlled cycles if you must ventilate.
• Increase inspection frequency during and immediately after warm spells.
• Document decisions and observations – warm spells are often where later disputes begin.

Wet loads or muddy harvest conditions that show up later
What’s happening: water and soil increase microbial pressure, reduce airflow through parts of the pile, and complicate wound healing. The result may not appear immediately – it can show up weeks later as hotspots, odour zones, and localized breakdown.

What you’ll often notice first:

• A localized sweet or musty odour
• A temperature zone that stays warm relative to its neighbours
• CO₂ drifting higher in one part of the building (if measured)

Which measurements matter most:

• Pile temperature mapping (warm zones)
• CO₂ trends and zone comparisons
• Fan run time and rationale (are you actually exchanging air in that zone?)
• Static pressure (if available – resistance can increase with soil and compaction)
• The logbook (you need to know which loads were wet and where they went)

What a sensible response looks like:

• Tighten monitoring in the suspected zone.
• Confirm distribution – wet, soil-heavy zones often become airflow problem zones.
• Avoid “panic cooling” that creates condensation risk.
• Document clearly – where the wet loads were placed and what you saw, when.

A persistent warm spot that does not respond to fan cycles
What’s happening: this is often either a distribution issue (air not moving through that zone) or a biological hotspot (respiration and breakdown generating heat). Sometimes it is both.

What you’ll often notice first:

• Temperature gradient that grows rather than shrinks
• Odour localized to that area
• CO₂ higher in that zone

Which measurements matter most:

• Pile temperature profile (confirm it’s persistent, not noise)
• Supply / plenum temperature (confirm the system is delivering what you think)
• CO₂ (trend direction and zone comparison)
• Static pressure (if available)
• Walk-through and documentation

What a sensible response looks like:

• Validate the measurement first (sensor error is common).
• If real, focus on distribution checks – air pathways, leaks, blockages, short-circuiting.
• Increase observation cadence and document everything.
• If odours and CO₂ suggest biological activity, prepare for targeted triage rather than hoping it disappears.

CO₂ creep – slow rise over weeks (often the quiet warning)
What’s happening: ventilation is not keeping pace with respiration – or dead zones are forming. CO₂ creep is often the “early chapter” of a later problem.

What you’ll often notice first:

• CO₂ rising gradually rather than spiking
• Fans running, but trend still rising
• Certain zones rising while others remain stable

Which measurements matter most:

• CO₂ trend (direction matters)
• Fan run time and rationale (are you ventilating effectively or just running fans?)
• Static pressure and distribution indicators
• Pile temperature trends (respiration and heat are linked)

What a sensible response looks like:

• Look for distribution issues first – rising CO₂ with fan run time is a common dead-zone signature.
• Validate sensor placement and accuracy if automated.
• Avoid overcorrecting with long fan runs during dew point risk periods.

Unexpected shrink and weight loss
What’s happening: overly dry air plus aggressive airflow can quietly remove more moisture than intended. Weight loss may not be obvious until you start handling or shipping.

What you’ll often notice first:

• Surface dryness near known airflow paths
• Increasing bruise sensitivity in handling
• A pattern of long fan runs during very dry weather

Which measurements matter most:

• RH trends (in context)
• Fan run time and rationale
• Outside air conditions (especially dry cold air events)
• Walk-through evidence near openings and air pathways
• Temperature stability (big swings can compound stress)

What a sensible response looks like:

• Review fan run patterns against outside conditions.
• Rebalance the system toward stability rather than continuous drying.
• Use walk-through checks to identify where dehydration is concentrated.

Sudden odour change (the “something shifted” moment)
What’s happening: odour often indicates biological change, moisture change, or both. It is one of the most valuable early warnings because it can appear before a problem is visible.

What you’ll often notice first:

• Odour localized to one area
• A subtle shift in wall frost, dampness, or surface conditions nearby
• Temperature or CO₂ beginning to diverge in that zone

Which measurements matter most:

• Walk-through observations (location matters)
• Pile temperature mapping
• CO₂ if available
• Dew point risk assessment (condensation often sits underneath odour changes)

What a sensible response looks like:

• Document the location and timing immediately.
• Cross-check temperature and CO₂ patterns in that zone.
• Increase monitoring frequency and avoid destabilizing fan decisions that introduce condensation risk.

What this baseline does – and does not – do

This baseline will not replace good agronomy, careful harvest handling, or appropriate sprout control programs. But it will reduce guesswork. It turns storage from reactive troubleshooting into measured management. In most storages, that shift alone protects both quality and profitability by spring.

Next in this series, PNT will take the same practical approach and focus on the first 30 days in storage – because that is where many later-season problems are quietly created.

Author: Lukie Pieterse, Potato News Today