4.3 Wineries / Breweries - Fermentation

Categories 31 and 1904

4.3.1 Introduction

Categories 31 and 1904 account for ethanol (which are considered part of TOG and ROG) emissions at wineries located in the San Francisco Bay Area (SFBA), resulting from the process of fermentation of grape juice to produce wine.

During the fermentation process, sugar in the grape juice reacts with yeast to form ethanol (alcohol) and carbon dioxide (CO2) gas. Ethanol escapes into the air through evaporation. The amount of ethanol formation is dependent on tank design, length of fermentation period, fermentation temperature, and volume and sugar content of fermenting juice.

Emissions from permitted sources within some wineries/breweries are covered under the point source category 31, while ethanol emissions from Bay Area wineries are estimated as an area source in category 1904. Emissions continue to be apportioned to these two source categories in a similar manner as that in the previous Emissions Inventory (EI) with a base year of 2011. The methodology for deriving emissions in Category 1904 is consistent with California Air Resources Board (ARB) Emissions Inventory Code (EIC) for Wine Fermentation [# 420-408-6090-0000 (47068)]34.

4.3.2 Methodology

Point Sources

Point Sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, for which the Air District has issued a permit to operate, e.g. refinery cooling towers. These could also be a collection of similar equipment / sources located across multiple facilities, e.g. reciprocating engines.

During the permit to operate (PTO) issuance process, the BAAQMD collects information from the operating facility and/or determines from published literature, e.g. EPA’s AP-42, characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. These characteristics are then stored for future use in the BAAQMD’s internal database. Facilities that hold a permit to operate are required to renew this permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the last 12 months. This throughput, in combination with the emission factors and controls factors stored in the internal database, are used to estimate annual emissions at the source level. These source level emissions are then sorted and aggregated into categories.

Further speciation and quality assurance of emissions are performed as a part of the inventory process. The BAAQMD staff also perform a systematic crosswalk between CEPAM’s source category classification (Emission Inventory Code - EICs) and the District’s source category classification (category identification number - cat_ids), which ensures consistency in the annual emissions reporting process (CEIDARS) to California Air Resources Board. The last part of the inventory development process includes forecasting and back casting, and aggregation into sub-sectors and sectors for documentation purposes. For those years where no data is available, emissions data are backcasted to year-1990, as well as forecasted to year-2040 using either interpolation or another mathematical approach (see Trends section). Finally, emissions trends spanning from year 1990-2040 for each category and pollutant are evaluated for anomalies that are then investigated and addressed.

Category 31 is considered a point source category and follows the above methodology for emissions estimates. Category 31 is nearly obsolete now with very few permitted sources from only a handful of wineries and green waste facilities being reported under this category. All TOG emissions from the fermentation process are entirely covered under category 1904, while combustion emissions and off-road ag equipment emissions from wineries in Bay Area are covered under other point sources and CARB source categories in the current base year EI, respectively.

Area Sources

Category 1904 is considered an area source category since it covers facilities / emission sources that are not directly permitted by the District, and hence not systematically cataloged. Emissions for area source categories are determined using the formula:

Current Year Emissions = Base Year Emission X Growth Profile, and,

Base Year Emission = Throughput X Control Factor X Emission Factor

where,

  • throughput or activity data for applicable base year(s) is determined using a top-down approach (e.g. state-, national-level data);
  • emission factor is derived from general literature, specific literature and reports, and/or source testing results provided by Air District staff;
  • control factor (if applicable) is determined by District and state rules and regulations in effect;
  • and, historical backcasting and forecasting of emissions is based on growth profiles as outlined in the Trends section of this chapter

The total emissions for category 1904 are determined by multiplying a composite wine fermentation emission factor and the regional wine production. The methodology is presently based on ARB’s methodology laid out in Section 5.1 (Food and Agriculture)1.

Certain assumptions are made in order to use available data to estimate ethanol emissions from wine fermentation at Bay Area wineries. These include –

  1. The quantity of grapes crushed in the State for each type of wine is proportional to the amount of that type of wine fermented.
  2. The relative ratios of red and white wines produced in California are representative of the split observed in Bay Area.
  3. The county fractions developed from county-apportioned wine fermentation process rates for year 2002, provided to ARB by the US. Alcohol and Tobacco Tax and Trade Bureau (TTB), can be held relatively constant up until base year 2015, in spite of significant increase in Bay Area wine production totals in 2015 as compared to 2002.

More details on throughput, county distribution, emission factors and controls is provided in the following subsections.

(a) Activity Data / Throughput

The throughput for this category is wine production which is derived from Wine Institute’s charts35 based on TTB data. The 2015 California wine production data (683,173,762 gallons) is scaled to 2002 data (491,352,590 gallons) to derive the Bay Area (BAAQMD jurisdiction) 2015 wine production data, since county-wise apportioned wine production data is available for year 2002 from TTB (via ARB1 in Table II).

(b) County Distribution / Fractions

The regional wine production data is apportioned to each Bay Area county on the basis of year 2002 county-specific wine fermentation process rates (Table II, ARB1). 68% of the wine fermented in the Bay Area originates in Napa county, while Sonoma county accounts for the next highest at 23%.

(c) Emission Factors

Ethanol emission factors from the two types of wine (White and Red) are derived from a computer model developed by Williams and Boulton36 as presented in ARB methodology documents. The ethanol emission factors produced for white wine, rose wine, and red wine are listed below:

\[ \text{TOG_e.f.}_{redrosewine} = \dfrac{6.2 \text{ lb}}{1000\text{ gallons}} \]

\[ \text{TOG_e.f.}_{whitewine} = \dfrac{2.5 \text{ lb}}{1000\text{ gallons}} \]

The relative proportion of the two types of wine fermented in California is based on the US Department of Agriculture’s National Agricultural Statistics Service (USDA NASS) Grape Crush Reports37 from base year 2015.

The amount of wine grapes crushed for red wine (55.1%) and white wine (44.9%) was used to estimate the ratio of these wines fermented in the State. A composite emission factor of 4.54 lb/1000 gal of wine fermented was derived by using this ratio of wine grape types crushed (see Sample Calculations).

The carbon dioxide (CO2) emission factor was derived from the chemical equation.

\[ C_{6}H_{12}O_{6} + \text{yeast} → 2\ C_{2}H_{5}OH + 2\ CO_{2} \]

Assume that fifty percent of CO2 emissions escaped to atmosphere during fermentation process, the CO2 emission factor of 157.41 lbs. per thousands of gallons of wine was estimated.
District’s Regulations 3, adopted on May 21, 2008, defined the carbon dioxide (CO2) emissions from wine fermentation processes was biogenic carbon dioxide emissions.

Category Total Organics (lb/1000 gal) Biogenic CO2 (lb/1000 gal)
1904 4.54 157.41

(d) Control Factors

Presently, no known District regulations or controls have been instituted on fermentation vessels to prevent ethanol emissions into the atmosphere.

(e) Speciation

This source category reports Total Organics Gas (TOG) emissions. Ethanol is a reactive Volatile Organic Compound (VOC) and all ethanol emissions are considered under Reactive Organic Gases (ROG). Hence the ROG / TOG ratio is equal to 1.

(f) Sample Calculations

A. Calculate statewide ratios of white and red wine production.

Determine the tons of grapes crushed for each type of wine compared to the total tons of grapes crushed for both types in 2015.

\[ \text{CA red wine fermentation ratio} = \dfrac{2,041,396.1 \text{ tons red wine grapes crushed}} {3,705,319.7 \text{ tons of both wine grapes crushed}} = 0.551 \text{ (55.1%)} \]

\[\text{CA white wine fermentation ratio} = \dfrac{1,663,923.6 \text{tons white wine grapes crushed}}{ 3,705,319.7 \text{tons of both wine grapes crushed}} = \text{ 0.449 (44.9%)}\]

B. Calculate composite emission factor.

\[ \text{TOG_e.f.}_{red wine} * 0.551 + \text{TOG_e.f.}_{white wine} * 0.449 = 4.54 \text{ lb/1000 gallons} \]

4.3.3 Changes in Methodology

No major changes in methodology were made in this version of the base year emissions inventory as compared to the previous EI. The only noticeable changes from the previous version include –

  1. ABAG’s latest employment projection data from Plan Bay Area 2040 is used to update the emissions forecast.

  2. The current composite emissions factor is based on base year 2015 data as compared to 2002 data that was used for the base year 2011 EI.

4.3.4 Emissions

A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication. TOG emissions from this category represent <1% of total TOG emissions from point and area source categories in the Bay Area.

4.3.6 Uncertainties

Some Bay Area wineries may have instituted emission controls that are not reflected here. Additionally, there are emission control regulations that have been applied to wineries in the Santa Barbara County by the local air quality regulatory agency in light of significant TOG emissions that have been observed from fermentation vessels. The emissions data derived here is strictly based on laboratory-derived emission factors from decades ago (1980s) and have not been validated through source tests. Hence actual emissions of ethanol released to the air can be significantly different.

4.3.7 Contact

Author: Abhinav Guha

Reviewers: Tan M. Dinh and Yuan Du

Last Update: November 06, 2023

4.3.8 References & Footnotes

  1. California Air Resources Board (CARB). 2005. Areawide Sources, Section 5.1 Food and Agriculture, Wine Fermentation. http://www.arb.ca.gov/ei/areasrc/fullpdf/full5-1.pdf.↩︎

  2. Wine Institute. 2020. California and US Wine Production. https://wineinstitute.org/our-industry/statistics/california-us-wine-production/↩︎

  3. L.A. Williams & R. Boulton. 1983. Modeling and Prediction of Evaporative Ethanol Loss during Wine Fermentation. American Journal of Enology and Viticulture, 32:234-242, (1983).↩︎

  4. California Agricultural Statistics Services. 2015. Grape Crush Final Report. https://www.nass.usda.gov/Statistics_by_State/California/Publications/Specialty_and^_Other_Releases/Grapes/Crush/Errata/2015/201608errata.pdf↩︎

  5. Association of Bay Area Governments. 2019. Plan Bay Area 2040. http://projections.planbayarea.org/↩︎