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Wildfire Smoke Taint: Managing the Risk in a Vineyard Purchase

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

Smoke taint is the smoky, burnt, ashy or medicinal character that can appear in wine made from grapes exposed to wildfire smoke. It comes mainly from volatile phenols released when wood burns: grapes absorb them, and some bind to grape sugars as glycosides that have no smoky aroma in the fruit but can contribute to taint in the finished wine. For a vineyard owner or buyer, the risk sits less in the land than in the crop, the grape contracts and the insurance.

Napa and Sonoma growers know the issue well. CAL FIRE records that the Glass Fire burned about 67,484 acres in Napa and Sonoma counties between September 27 and October 20, 2020, during harvest. In its preliminary 2020 Grape Crush Report summary, CDFA said prices reflected adjustments for smoke damage as reported by purchasers. This page explains the science in plain terms, how testing works, how contracts and crop insurance allocate the risk, and what to ask when buying or selling a vineyard.

What causes smoke taint

The Australian Wine Research Institute (AWRI), one of the main research bodies on the subject, identifies free volatile phenols in smoke as the main cause. Guaiacol and methylguaiacol are among the compounds labs measure. Once absorbed, some of these phenols bind to sugars in the grape, forming glycosides that aren’t detectable by smell in the fruit.

AWRI says grapes are at risk from exposure at any stage after cap-fall is complete (growth stage E-L 26). It names four main factors in how much a crop is affected:

the growth stage of the vines when smoke arrives;
the grape variety;
the composition of the smoke; and
how long the exposure lasts.

Those factors vary from block to block and from one fire to the next, so the distance to a fire doesn’t settle the question on its own. AWRI points growers to laboratory analysis rather than visual inspection.

What UC Davis research has looked at

At UC Davis, Cooperative Extension Specialist Anita Oberholster’s lab took up smoke research after the 2017 wildfires affected grapes at the university’s Oakville Experimental Station. A January 2018 UC Davis update described 48 individual ferments made from smoke-affected grapes from Napa, Sonoma and Humboldt counties, used to compare winemaking approaches such as oak products, enzymes, skin contact time, fermentation temperature and yeast.

An August 2019 UC Davis update reported a sobering result for red wines: extraction of volatile phenols from the grapes happened so quickly that no protocol tested significantly changed the wine in the long term, though the outcome depended partly on the level present. The lab’s later work focused on remediation techniques and on relating phenol profiles to how the wines taste.

For a property owner the lesson is practical. Winemaking can’t reliably fix heavily affected red fruit, so the economic risk falls on whoever owns the crop when smoke arrives, unless a contract or policy shifts it.

How grapes and wine are tested

Testing serves two purposes: deciding whether to pick and deliver, and documenting the fruit’s condition for a buyer, a winery or an insurer.

Test	What it measures	Limits
Free volatile phenols in berries	Smoke markers such as guaiacol and 4-methylguaiacol already present in the fruit	Misses bound forms; some varieties, notably Syrah, contain guaiacol naturally
Bound (glycosylated) phenols	Phenols tied to sugars that can contribute to taint later	ETS Laboratories did not offer it in 2020; check current availability and turnaround
Small-lot or micro-ferment	A small wine made from the fruit, analyzed and tasted	Takes longer; still a prediction of production wine
Finished wine analysis	Smoke markers in wine after fermentation or aging	Comes too late for picking decisions

AWRI recommends analyzing grapes for both volatile phenols and the glycosides, and suggests sampling about three weeks before harvest so results arrive in time. It also describes small-scale ferments as a way to judge the likely sensory effect.

ETS Laboratories, a wine analysis lab in St. Helena, published a smoke bulletin during the 2020 harvest; the copy we reviewed is hosted by El Dorado Winegrape Growers. It asked for about 250 undamaged berries per sample, warned against mixing varieties in one sample because uptake differs by cultivar, and said a sample about 7 to 10 days before harvest was typical, adding that an early negative result could be misleading because exposure is cumulative. The bulletin noted that Petit Verdot is often more affected than other varieties. Test menus have changed since 2020, so check each lab’s current panel, sampling instructions and turnaround before harvest.

Smoke clauses in grape contracts

When a vineyard sells fruit, the grape purchase agreement usually decides who carries smoke risk. A published Duckhorn Wine Company grower agreement, discussed in our guide to grape purchase agreements, requires fruit free of smoke taint and other contaminants as the winery determines. Language like that puts the fire-year risk largely on the grower.

Points worth negotiating, or checking in a contract you would take over:

Who decides. A named lab, an agreed test and agreed thresholds are more predictable than a winery’s sole judgment.
When. Deadlines for testing, for the winery’s decision and for notice to the grower, so fruit isn’t left hanging.
How much. Rejection by block or load rather than the whole crop, and whether the grower may sell rejected fruit elsewhere.
Payment. Whether any price is paid for fruit that tests above threshold, and who pays for testing.
Force majeure. Whether a fire lets either side cancel the year’s undelivered fruit.

Leased vineyards raise the same question in a different form. Under a vineyard lease, the tenant usually owns the crop, so smoke risk sits with the tenant unless the lease says otherwise; check how rent is set in a fire year.

Crop insurance: the FIP-SI endorsement

USDA’s Risk Management Agency (RMA) announced the Fire Insurance Protection – Smoke Index (FIP-SI) endorsement on August 12, 2024, for California grapes starting with the 2025 crop year. As of October 2026, RMA’s program page says it is available for grapes in California, Idaho, Oregon and Washington, in counties listed in the grape actuarial documents, for the 2026 crop year and beyond.

How it works, according to RMA:

It covers a portion of the deductible under the Grape Crop Provisions when a county has enough Smoke Events. The 2024 announcement defined a Smoke Event as a day with heavy smoke density as determined by NOAA’s Hazard Mapping System Smoke Product.
It is area-based. It protects against widespread loss in a county and doesn’t look at an individual vineyard’s yield or revenue, so a grower can have a loss and receive no FIP-SI payment, or the reverse.
No notice of loss is required, and payments are made after the insurance period ends.
It has its own premium and administrative fee in addition to the underlying policy, and for 2026 and later its sales closing date matches the underlying grape policy.

FIP-SI is a supplement, not a full smoke policy. Ask a licensed crop insurance agent how the underlying grape policy treats smoke-related quality loss on your blocks and what records it requires. Insurance for buildings, equipment and winery operations is a separate market; see our guide to vineyard and winery insurance, and for residences on the property, the California FAIR Plan.

Due diligence for vineyard buyers

A buyer can’t remove smoke risk, but can price it and allocate it. Add these items to the standard vineyard due diligence list:

Fire and hazard history. Check the property’s fire hazard severity zone and nearby fire history; our guide to fire hazard severity zones in the North Bay explains the official maps.
Vintage-by-vintage crop records. Tons, prices, rejection notices and any smoke test results for each recent year, especially fire years.
Contracts. Smoke language, testing protocols, notice dates and whether contracts pass to a new owner.
Insurance history. Crop policies in place, whether FIP-SI was elected, claims filed and payments received.
Wine inventory. For a winery, analysis of any vintages that went through a fire season, before inventory is valued; our winery due diligence checklist covers the rest.
The crop at closing. If escrow closes during the growing season, state in the purchase agreement who owns the hanging crop and who bears a loss if smoke arrives before harvest.

Fire years also affect value. An appraiser using an income approach will look at whether a year’s low revenue reflects the property or a one-time event; our vineyard valuation guide explains how income is normalized. Buyers looking at hillside and upvalley properties, for example around Angwin and Calistoga, should also budget for wildfire mitigation on the homes and buildings; see our post on home hardening.

For growers selling a vineyard

Good records reduce the discount a buyer applies for uncertainty. Before listing, gather test results, winery correspondence and insurance documents for each fire year, and be ready to explain what happened to the fruit. A clear file showing contracts that held through a fire season can be a selling point. Our guide to selling a vineyard covers the rest of the preparation.

Questions people ask

What causes smoke taint in wine?

Mainly volatile phenols from burning wood that grapes absorb from smoke. Some bind to grape sugars as glycosides with no smoky aroma, which is why fruit can taste normal and still produce a tainted wine.

Can you see or taste smoke taint on the grapes?

Not reliably. AWRI points growers to laboratory analysis of both free volatile phenols and their bound forms, and to small-lot ferments, rather than visual checks.

When should grapes be tested for smoke?

AWRI suggests sampling about three weeks before harvest so results come back in time. ETS Laboratories’ 2020 bulletin described a sample about 7 to 10 days before harvest as typical and warned that early negatives can mislead, so testing again closer to harvest can make sense.

Can a winery reject grapes for smoke taint?

If the grape contract allows it. Many contracts require fruit free of smoke taint, sometimes as the winery determines. Read who tests, what thresholds apply and the deadline for a decision.

Does crop insurance cover smoke taint?

USDA’s FIP-SI endorsement covers part of the grape policy deductible when a county records enough heavy-smoke days, without looking at an individual vineyard’s loss. Ask a crop insurance agent how the underlying grape policy handles smoke damage.

Does a past fire lower a vineyard’s value?

Not by itself. What matters is the effect on income, contracts, insurance and the property’s condition. An appraiser using an income approach will ask whether a weak year reflects the property or a one-time event, so complete records help.

This is general information, not legal or insurance advice; have a California agricultural attorney review the smoke terms in any grape contract or vineyard purchase, and a licensed crop insurance agent explain your coverage.

Looking at a vineyard that has been through a fire season, or preparing to sell one? We can help you assemble the records and frame the questions; see our vineyard and winery services or contact us.

Sources & notes

Last reviewed October 2026 by Matthew Martinez.