Could Your Pod Coffee Brewer Be Making You Sick?

• Benefits of coffee – In an umbrella review by Poole et al 2017, the authors reviewed 201 meta-analyses of observational research and 17 meta-analyses of randomized controlled trials and reported that compared to non-coffee drinkers, coffee consumes were shown to have a 19% relative risk reduction for mortality from cardiovascular disease. Additionally, the largest reduction in relative risk of all-cause mortality was found in groups that consumed 3 cups of coffee compared to none. A high intake of decaffeinated coffee was also associated with reduced all-cause mortality risks.
• Does it harm? – Wikoff et al 2017 reviewed the health risks with caffeine consumption and found that in healthy adults, less than 400mg/day had no adverse effects. However, there are known harmful associations between caffeine and pregnancy. Caffeine consumption during pregnancy has been shown to be associated with low birth weight and pregnancy loss at greater than 300mg/day in pregnant women.

Summaries:

• Caffeine contains natural alkaloids with antibacterial properties – but is not expected to be able to suppress bacterial build-up in a coffee maker. Bacteria can easily grow in warm and damp environments making the coffee pot a potentially ideal environment for bacterial growth. Many bacterial species like Enterococcus species and Pseudomonas species were found in the drip trays of coffee makers like Keurig and Nespresso (Vilanova et al 2015), but the bacteria present are mostly present within the environment.
• Bacterial colonization of the coffee machine can occur quickly, bacterial species are detectable as early as 4 days after usage and over time the bacterial diversity grows. (Vilanova et al 2015).
• In fully automated domestic coffee machines, the mean total viable count of bacteria found on all outlets (including the coffee output and water reservoir) was 2.24×10³ colony forming units/ml (Schages et al 2018). The bacteria found there were also found on the human skin flora (Staphylococcus epidermidis) or ubiquitous within the environment. Researchers found that domestic automated coffee machines also had higher total viable counts of bacteria than commercial automated coffee machines which they suggest is due to improper or infrequent cleaning.
• Cappuccino machines had higher total viable counts possibly due to improper cleaning of the milk frother and inner tubing. (Schages et al 2018).
• The National Sanitation Foundation International completed a household study in 2011 which swabbed various areas in 22 households. 31% had yeast or mold present in the home and 50% of those with yeast/mold had yeast/mold present in their coffee reservoirs. The germ count (including mold, yeast, coliform, and E.coli) in the coffee maker was higher per 10 sq centimeters than on a toilet seat (548,270 per 10 sq cm in coffee reservoir vs 515 per 10 sq cm on toilet seat). 9% of homes had coliform in their coffee reservoirs. In a follow-up study of college students’ homes in 2016, coffee makers were found to have had the highest percentage of mold in the home.

 Studies:

• Bacteria accumulates in the drip tray
  • Vilanova et al 2015 – This article provides the first systematic analysis of coffee machine-associated bacteria. Researchers sampled the coffee waste reservoir, inner drip tray (located below the capsule container) of 10 different Nespresso machines (10 domestic and 10 semi-domestic). Samples from 9 Nespresso machines were in operation for at least one year. One new Nespresso machine was sampled independently. Bacteria were identified via high throughput sequencing and analysis of 16S ribosomal RNA gene amplicons. 35-67 bacterial genera were represented in the coffee machines. Main taxa of bacteria: Enterococcus species and Pseudomonas (moderately to highly abundant in 9/10 machines) Others included: Stenotophomonas, Acinetobacter, and Sphingobacterium spp.
  • There were no differences in bacterial sequences detected between models used for domestic (2-4 uses per day) or commercial usage (10-20 uses per day).
• About the bacteria present:
  • Pseudomonas has been known to catabolize coffee and other species, such as Acinetobacter, Stenotrophomonas, and Curtobacterium species are frequently associated with presence with coffee.
• Colonization study:
  • Using a new Krups Inissia Nespresso machine, bacterial colonization was monitored over a 2 month time period. The authors found that bacterial diversity was highest initially and decreased after 14 days.
    • 4-11 days after usage = Enterobacteria (genus Pantoea)
    • 14-21 days = Firmicutes (genera: Bacillus, Terribacillus, Paenibacillus)
    • 28 days = Sphingomonadales (gen. Sphingobium)
    • 31 days = Actinomycetales (gen. Curtobacterium)
    • 49 days = Pseudomonadales (gen. Acinetobacter)
    • After 2 months, Enterococcus and Pseudomonas predominated.
  • Some of these genera include potentially pathogenic bacteria species – but during this study, they did not attempt to isolate/verify the presence (or absence) of specific pathogenic species within these groups.
  • General conclusion: Coffee leach from standard capsule coffee machines can be rich substrates for bacterial growth. Interestingly, ecological succession is occurring within coffee machines (generalist bacteria appearing first → coffee-adapted variable bacteriomes developing over time). The bacteria that are present are likely from the environment, not from the capsules themselves (no microorganisms or bacterial DNA was detected on the coffee capsules).
  • Possible applications:
    • The outside of the coffee machine and drip tray should be cleaned to prevent build-up of bacteria.
• Bacteria can be present in the brewed coffee
  • Schages et al 2018 – Determined the microbial load of random coffee samples from automated machines and monitored the influence of temperature. The authors utilized 50 coffee and 50 cappuccino samples from commercially automated coffee machines and 10 coffee samples from private machines and looked for microbial contamination by swabbing the coffee output, base of the water reservoir at the inlet pump (in domestic), and multi-use mugs. They found that in private households mean total viable count (TVC) of bacteria was 4.47×10² cfu/ml (colony forming units per mL) at the coffee output and 3.33 x10³ cfu/ml at the water reservoirs; the mean TVC (total viable count of bacteria) for all outlets was 2.24×10³ cfu/mL. For commercial machines; no microbes were detected at temperatures of 64C (147 F) or higher.
    • • Mean TVC in brewed coffee
        • Brewing temperature less than 62C = 2.85×10^2 cfu/ml
        • Brewing temperature 62-64C = 6.47×10^1 cfu/ml
      • Mean TVC in cappuccino samples
        • Brewing temperature less than 60C = 4.19 x10^2 cfu/ml
        • Brewing temperature 60-62C = 6.28 x 10^1 cfu/ml
        • Brewing temperature above 62C = no microbes
      • The authors suggest that higher TVC in cappuccino may indicate increased contamination due to the milk frother not being appropriately cleaned.
• There was lots of variability in the samples, but overall commercial machines did see a significantly lower viable count of bacteria with higher temperatures (however, with controlled bacteria inputs (see ‘Higher temperatures study’) that was not recapitulated)
• Some of the microorganisms found in brewed domestic coffee were:
  • Bacillus cereus –Schneider et al 2017 Can form heat-resistant endospores, ubiquitous within the environment, associated with food spoiling.
  • Bacillus licheniformis – May also cause food-borne illnesses (Logan et al 2011)
  • coli – Most are harmless, some may cause food-borne illnesses (CDC)
  • epidermidis – Skin microflora – possibly transmitted from cleaning/regular maintenance
• Some of the microorganisms found in the domestic water reservoir were:
  • Pseudomonas aeruginosa
    • Ubiquitous in the environment (soil, water, plants)
    • Can affect patients in hospital settings (hospital-acquired infections) (CDC)
    • Can form biofilms (Tam Tran Thi 2020)
• Some of the microorganisms found in the domestic coffee outlet were:

• • Pseudomonas aeruginosa
  • epidermidis
  • Candida pararugosa
    • Isolated from human feces (thought to colonize the GI); rare to cause infection but possible (Piatti et al 2021)
  • Total viable counts of bacteria were higher in households vs commercial coffee machines. This was suggested to be due to improper cleaning at home or a lower frequency of cleaning at home.
  • Higher temperatures study:
    • Measured effect of temperature from a domestic machine (min, med, max settings) and determined remaining bacterial load after artificially inserting commonly found bacteria in coffee into 1L of water within the water reservoir. Calculated the logarithmic reduction factor (difference between initial load and final load in brewed coffee) to determine whether or not brew temperature had antimicrobial effects – there were no significant differences in logarithmic reduction factor (calculation- log10 (initial microbial load) – log10 (remaining bacterial load) between temperatures whencoli was deliberately added to the coffeemaker.
  • Possible applications:
    • Increasing temperature won’t kill all bacteria, but overall there may be a slight reduction (but not statistically significant)
    • Authors suggest an unclean machine (increased microbial contamination) contributes more to bacterial load in brewed coffee rather than reusing a dirty mug.

NSF -College Germ Study

• In 2016, the National Sanitation Foundation International (an independent organization that oversees quality/safety of consumer productions internationally) had college students from southeast Michigan swab their homes for the germiest areas and looked for E.coli, Coliform, MRSA, yeast, and mold. They found that out of those groups, coffee makers had the highest percentages of mold present. (In decreasing order – Mold, Yeast, Coliform, E. coli)- this study is quoted frequently, but they didn’t share the data with the public; only the press release and infographic were shared. It’s unclear what locations were swabbed.
  • Cleaning coffee maker – NSF – they suggest clean with soap and water after every use; weekly vinegar/water or cleaning solution
  • NSF – Infographic

2011 Household Germ study (detailed) – NSF

• 22 households had various areas of their home swabbed and found that 31% of households tested had yeast/mold present (greater than 10 CFU per sq. cm.)
  • 50% of those with yeast/mold in their homes had it in their coffee reservoirs
• Coliform bacteria was found in 81% of homes
  • 9% had it in coffee reservoirs
  • No staph aureus or E.coli was found in the coffee reservoirs
• The average normalized count of germs (including mold, yeast, coliform, and E.coli) was:
  • 548,270 per 10 sq. cm in the coffee reservoir
  • 515 per 10 sq. cm found on the toilet seat
  • NSF-infographic

• How quickly does it appear?
  • Colonization of specific types of bacteria start as early as D4 post-use (Vilanova et al 2015)

Are there coffees with fewer bacteria?

From the available data, studies have not investigated cleaning practices (or lack thereof) in relation to bacterial buildup between coffee makers (types or brands of coffee); instead – general consensus appears to be that bacteria build-up can occur with any coffee maker (regardless of the make/model) with lack of cleaning and due to the coffee makers being exposed to environmental sources of bacteria (for example, from skin). CONCLUSION – ANY COFFEE MAKER WILL BREED BACTERIA IF IT’S NOT WASHED (IE EVEN A FRENCH PRESS)

• Keurig says
  • Brewer
    • Wipe exterior with soap and water, clean drip tray with soap and water
    • Clean water reservoir once a week; don’t dry the water reservoir
    • Run a water-only brew
    • Use a Keurig rinse pod for the freshest coffee taste
  • Brewer needles
    • Remove pod holder and pod funnel
    • Use a metal paper clip to unclog the exit needle and entrance needle to loosen particles
    • Replace pod holder
    • Run 2 water only brews
  • Brewer needles 2.0
    • Use brewer maintenance accessory (only works for certain models); fill with water and place in the pod holder
    • Close Keurig multiple times to release coffee grounds from the entrance/exit needle
    • Run 1 cleaning brew (water only) largest size
    • Clean brewer maintenance accessory with water
  • Descaling
    • Keurig recommends descaling brewer to remove calcium deposits every 3-6 months using Keurig Descaling Solution
    • Water/vinegar solution is also widely used and suggested – I.e –Good housekeeping

• Nespresso says
  • Wipe down and purge the steam wand after each use
  • Clean the milk container after each use (either hand wash or dishwasher)
  • Descale every 6-12 months (with Nespresso descaling kit)
    • Nespresso does NOT recommend using vinegar because it can damage the machine
  • Other versions:
    • Some have a water tank reservoir that should be cleaned before refilling with water
    • Cup support, capsule container, drip tray suggested daily for some models
  • Nespresso has lots of different types of coffee makers ranging from simple to very high-end complexity; based on the nature of the more complex machines (more parts, more pipes, more areas that require regular maintenance – these types are likely capable of building up more bacteria if not cleaned properly.

• Mr. Coffee says
  • Drip coffee maker and automatic drip coffee maker
    • Descale once a month with vinegar and rinse water through
    • Use mild, non-scented soap, coffee cleaning solution, or white vinegar to clean
    • Empty pot and rinse with water after making coffee to prevent build-up
    • Wipe out pot every night
  • Espresso maker
    • Remove grounds from the filter, wash filter, and cup with soap/water
    • Use clean cycle to clean milk froth tubing
    • Dispose of milk and wash milk reservoir with soap and water
    • Empty water, wash reservoir (empty if will not be using)
    • Clean drip tray with soap and water
    • Unplug the machine, wet paper towel, and wipe off brew head to remove coffee grounds

• • Vinegar and cleaning
    • String et al 2020 – Investigated efficacy of bleach, boiled water, soapy water, and 5% vinegar’s ability to remove biofilms from household taps. Biofilms can develop in drinking water distribution systems (pipes/tubing/taps). Soapy water did reduce E.coli on surfaces, but required scrubbing and worked best when taps were disassembled. Vinegar is not listed or studied as a disinfectant by the EPA (EPA), but it has been shown to help thin biofilms from water taps (when taps are disassembled and scrubbed/soaked in 5% acetic acid vinegar). Vinegar was able to reduce E.coli to less than 1 cfu/cm² from vertical and horizontal surfaces on water taps. Soapy water wasn’t able to remove biofilms; but did reduce E.coli on surfaces of taps.
    • This study is looking at water taps which are harder to disassemble- vinegar doesn’t kill all bacteria. But it may be beneficial to descale with some potential additional benefit of killing some E.coli and some reduction in biofilms to extrapolate some application from this study.

• Others say
  • Goodhousekeeping – Drip Coffee Maker cleaning
    • Wash removable parts with soap after every use
    • Monthly descaling
    • Wash carafe after each use with water/soap
    • Can add a little rice (also recommended by Mr.Coffee) and clean with a scrub sponge to remove debris for additional shine.
  • Goodhousekeeping – Keurig
    • Weekly – clean mug tray/k-cup holder, wipe inside of water reservoir (after removing filter) with a soapy cloth and rinse, air dry, wipe exterior surfaces, replace all parts
    • Bi-monthly = replace water filter cartridge
    • Every 3-6 months = Descale machine (vinegar or Keurig descaling solution)
    • As needed = clean Keurig needles
  • Cleaning coffee maker – NSF
    • (2011 recommendations) Vinegar – let stand for 30 minutes, then run vinegar through the unit. Clean every 40-80 brew cycles or monthly.
    • (2016 recommendations) Wash with soap/water after each use; weekly clean with vinegar.