Grinding coffee beans stored in a frozen bean cellar without defrosting? - Page 3

Grinders are one of the keys to exceptional espresso. Discuss them here.
mbeck

#21: Post by mbeck »

Frozen beans, directly into the grinder. Temp from my probe thermometer, post grind, in the catch cup: 62.1F. Ambient temperature 68F. Niche grinder, at 20 for a light-medium roast espresso.

K7

#22: Post by K7 »

1. Filter --> much coarser than espresso --> temperature rise from grinding is less than for espresso --> need hotter water to compensate for cooler ground coffee

2. Heat capacity of dry coffee is thought to be around 40% of water. Meaning if I pull espresso at 1:2 ratio and use the same input water temp, I would be brewing at 0.4/2 = 0.2 C cooler for ground coffee that is 1 C cooler. i.e. If my frozen beans end up being 1 C cooler after grinding (compared to unfrozen), I would be brewing 0.2 C cooler, which is hardly noticeable. If they were 5 C cooler after grinding, I would be brewing 0.2*5 = 1 C cooler, which is probably noticeable in taste.

When I ground frozen beans a couple times in the past, it felt noticeably cooler to touch. Haven't measured it with a thermometer, though.

Looking forward to JohnB's second measurement.

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JohnB.
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#23: Post by JohnB. »

Just to follow up: grinding the room temp beans produced an 88°F puck after tamping so 11°F difference from the frozen bean puck. Probably this varies depending on what grinder you are using & your room temp. No idea how much the 11°F cooler puck temp would effect the resulting shot temp as it's being soaked with 200°F or higher water. Hasn't been an issue for me as 98% of my shots are in the 198°F-204°F temp range & the temps that work best are typical for the bean/blend I'm using.
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jpender

#24: Post by jpender »

JohnB. wrote:No idea how much the 11°F cooler puck temp would effect the resulting shot temp as it's being soaked with 200°F or higher water.
It depends on the coffee ratio, as well as any thermal losses.

Scott Rao did a very simplified calculation in his book The Professional Barista's Handbook. He basically calculated the equilibrium temperature you would get if you mixed the grounds with water in a perfectly insulated container.

For your example, assuming a 1:2 ratio, you'd expect about 2°F difference in the equilibrium temperature. By the same token, different ratios would also theoretically affect the puck temperature. A 1:1 ratio would lower the equilibrium temperature by 12°F.

Of course in a real shot you wouldn't see just one temperature in the puck; it would be a profile where there would initially be a difference that would get smaller as the shot progressed.

jpender

#25: Post by jpender »

My freezer:



You can see just past the 4 hour mark where my wife opened the freezer twice to get brownies to eat!

One idea about frost-free freezers is that even though they don't melt your food they do raise the air temperature. That would tend to increase sublimation which in turn would perhaps worsen freezer burn on foods. Coffee is already very dehydrated and moisture makes coffee degrade faster. So it seems unlikely that additional dehydration of coffee beans would be a problem. But who knows, a varying temperature could have some other negative effect on stored coffee. Maybe a true coffee geek would own a -70°C freezer.

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JohnB.
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#26: Post by JohnB. »

If that freezer is still in warranty you might want to contact the company & ask what the normal temp range is. My old FF Frigidaire has been running 24/7 since 2004 & the only time it's hit 23°F was when something on one of the shelves kept the door from sealing properly. Luckily the alarm saved us that time.
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Brewzologist
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#27: Post by Brewzologist »

I've had a bank of frozen liquid yeasts for over 10 years which I spin up to a larger volume for beer brewing. I added glycerol to the yeast which helps reduce cell wall damage from temperature changes. For this application, a very cold deep freezer is paramount for keeping the yeast alive. I also use a deep freezer for my green coffee which may be stored for years too.

Point is, for roasted coffee I'd agree that it's fine to store it in an auto-defrost freezer since it's likely to get consumed before damage happens. And a trick I learned too was that I could store my yeast in a small cooler with ice packs that in turn was stored inside an auto-defrost freezer which rendered moot the effects of temperature changes. Those concerned with auto-defrost freezers effect on roasted coffee could try this too.

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#28: Post by JohnB. »

I've been storing roasted coffee in our FF freezers since 2008 & green coffee since 2009. Roasted coffee keeps 6 months+ in vacuum sealed jars & the vacuum sealed greens seem to keep as long as you want. Currently brewing some Yemen Mohka Ismali purchased from Sweet Marias in 2012 that I recently roasted. Still smelled like fresh greens when I opened the vacuum sealed bag, roasted fine & tastes fine. Our blueberry & garden harvests (corn/blacked peas/lima beans/ect) keep 2-3 years without issues. If my Frost Free freezers are damaging our foods/coffees it must be a VERY long drawn out process.
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jpender

#29: Post by jpender »

JohnB. wrote:If that freezer is still in warranty you might want to contact the company & ask what the normal temp range is. My old FF Frigidaire has been running 24/7 since 2004 & the only time it's hit 23°F was when something on one of the shelves kept the door from sealing properly. Luckily the alarm saved us that time.
Ha! Thanks for your concern but I believe our 19 year-old refrigerator/freezer is working perfectly. If you surf the internet you will find references to air temps in the mid-20s during defrost. Here's one supposedly for a Frigidaire model:




There isn't going to be a freezer compartment air temperature specification for defrost since it will depend upon what's in your freezer and probably the location of the probe too. The defrost thermostat for my freezer opens at 55°F. That's how hot it will be at the back of the freezer, behind the panel, when the heat is shut off. The fan is off during defrost so the heat flux into the main compartment will be due primarily to convection.

Our freezer is stuffed pretty full right now. I would imagine that the fuller the freezer the hotter the air gets during defrost simply because there is less air in a full freezer. The surface area of frozen items doesn't change as much with how full the compartment is. It would also depend on what is in the freezer. Items that are packaged in such a way that they are well insulated will result in warmer air during defrost. At the moment we have almost no ice and everything is wrapped up in plastic.

The user manual says to test the temperature by putting a thermometer between two items in the freezer. That will dampen the oscillations and give a more useful number. Maybe I'll try that and see what the defrost cycle does in that case. They seem to be coming every 16 hours or so. If I'm doing the math right another one is due in a few hours.

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JohnB.
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#30: Post by JohnB. »

jpender wrote:Ha! Thanks for your concern but I believe our 19 year-old refrigerator/freezer is working perfectly. If you surf the internet you will find references to air temps in the mid-20s during defrost.
As I posted we had to have the door ajar to get a mid 20°F temp rise in our 17 year old 21 cu ft Frigidaire. I cleared the high/low reads on the temp monitor yesterday & will see where it goes this week. After 16 hours max temp was 8.9°F/51% humidity. Dropped back to -1°F/38% & settled in at 4°F/43% which is where I normally see it. Like yours the freezer is full, no ice or frost showing.
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